Mooncake Store Python API

Installation

PyPI Package

Install the Mooncake Transfer Engine package from PyPI, which includes both Mooncake Transfer Engine and Mooncake Store Python bindings:

pip install mooncake-transfer-engine

📦 Package Details: https://pypi.org/project/mooncake-transfer-engine/

Required Service

The only always-required service is:

• mooncake_master — Master service for cluster membership and object placement

For Transfer Engine metadata, use the P2PHANDSHAKE connection string for decentralized peer discovery, enable the master’s embedded HTTP metadata server, or provide an external metadata service.

Quick Start

Start Master (with HTTP enabled)

Enable the built-in HTTP metadata server when starting the master:

mooncake_master \
  --enable_http_metadata_server=true \
  --http_metadata_server_host=0.0.0.0 \
  --http_metadata_server_port=8080

This exposes the metadata endpoint at http://<host>:<port>/metadata.

Hello World Example

from mooncake.store import MooncakeDistributedStore

# 1. Create store instance
store = MooncakeDistributedStore()

# 2. Setup with all required parameters
store.setup(
    "localhost",           # Your node's address
    "http://localhost:8080/metadata",    # HTTP metadata server
    512*1024*1024,          # 512MB segment size
    128*1024*1024,          # 128MB local buffer
    "tcp",                             # Use TCP (RDMA for high performance)
    "",                            # Leave empty; Mooncake auto-picks RDMA devices when needed
    "localhost:50051"        # Master service
)

# 3. Store data
store.put("hello_key", b"Hello, Mooncake Store!")

# 4. Retrieve data
data = store.get("hello_key")
print(data.decode())  # Output: Hello, Mooncake Store!

# 5. Clean up
store.close()

RDMA device selection: For protocol="rdma" or protocol="efa", leave rdma_devices as "" to auto-discover NICs. Set MC_MS_AUTO_DISC=0 when you want auto-discovery disabled, then provide a comma-separated list such as "mlx5_0,mlx5_1" to pin specific hardware.

Mooncake selects available ports internally at setup() , so you do not need to fix specific port numbers in these examples. Internally, ports are chosen from a dynamic range (currently 12300–14300).

P2P Hello World

The following setup uses P2P handshake and does not require an HTTP metadata server. Pass the literal P2PHANDSHAKE value as the metadata server.

from mooncake.store import MooncakeDistributedStore

store = MooncakeDistributedStore()
store.setup(
    "localhost",           # Your node's ip address
    "P2PHANDSHAKE",              # P2P handshake (no HTTP metadata)
    512*1024*1024,                # 512MB segment size
    128*1024*1024,                # 128MB local buffer
    "tcp",                       # Use TCP (RDMA for high performance)
    "",                          # Leave empty; Mooncake auto-picks RDMA devices when needed
    "localhost:50051"           # Master service
)

store.put("hello_key", b"Hello, Mooncake Store!")
print(store.get("hello_key").decode())
store.close()

Basic API Usage

Simple Get/Put Operations

Click to expand: Complete Get/Put example with NumPy arrays

import numpy as np
import json
from mooncake.store import MooncakeDistributedStore

# 1. Initialize
store = MooncakeDistributedStore()
store.setup("localhost",
            "http://localhost:8080/metadata",
            512*1024*1024,
            128*1024*1024,
            "tcp",
            "",
            "localhost:50051")
print("Store ready.")

# 2. Store data
store.put("config", b'{"model": "llama-7b", "temperature": 0.7}')
model_weights = np.random.randn(1000, 1000).astype(np.float32)
store.put("weights", model_weights.tobytes())
store.put("cache", b"some serialized cache data")

# 3. Retrieve and verify data
config = json.loads(store.get("config").decode())
weights = np.frombuffer(store.get("weights"), dtype=np.float32).reshape(1000, 1000)

print("Config OK:", config["model"])
print("Weights OK, mean =", round(float(weights.mean()), 4))
print("Cache exists?", bool(store.is_exist("cache")))

# 4. Close
store.close()

Structured Object Store Helper

mooncake.structured_object_store provides a higher-level helper for one logical object that contains multiple named members. It is designed for cases such as rollout / batch transfer where callers want to keep their own object semantics locally while using Mooncake for fast payload movement.

The helper separates two concepts:

• structured object path: named members with metadata-aware materialization;

• generic bundle path: manifest + named payloads when the caller only needs raw grouped objects.

Main types

from mooncake.structured_object_store import (
    MooncakeBundleTransfer,
    StructuredMemberSlice,
    StructuredObjectPayload,
)

• MooncakeBundleTransfer: public helper facade built on a MooncakeDistributedStore.

• StructuredObjectPayload: structured object to write. Members are passed in buffers, and optional object metadata is passed in metadata.

• StructuredMemberSlice: slice selection for one structured member during reads.

Structured object write and full read

Use put_structured_object() to write one structured object. The default read path is read_spec(ref), and full-object materialization is just the default case of the partial-read API.

import numpy as np
from mooncake.store import MooncakeDistributedStore
from mooncake.structured_object_store import MooncakeBundleTransfer, StructuredObjectPayload

store = MooncakeDistributedStore()
transfer = MooncakeBundleTransfer(store, key_prefix="demo/structured")

payload = StructuredObjectPayload(
    metadata={"step": 7, "layout": "rollout"},
    buffers={
        "tokens": np.array(range(24), dtype=np.int32).reshape(6, 4),
        "mask": np.ones((6, 4), dtype=np.int8),
        "prompt_ids": b"sample-ids",
    },
)

ref = transfer.put_structured_object(payload)
result = transfer.materialize(transfer.read_spec(ref))

tokens = result.objects["tokens"]
prompt_ids = result.objects["prompt_ids"]
metadata = result.metadata

Structured object transfer policy

By default, structured object writes use BundleTransferPolicy(copy_mode="auto"). Non-tensor payloads are staged through a Mooncake BufferPool and written with batch_put_from when that path is available; otherwise Mooncake falls back to ordinary store.put. Typed-ragged ndarray rows use the native fast-copy extension to copy directly into the staging buffer without an intermediate concatenation.

Use copy_mode="copy" to force the regular store.put path:

from mooncake.structured_object_store import BundleTransferPolicy

ref = transfer.put_structured_object(
    payload,
    policy=BundleTransferPolicy(copy_mode="copy"),
)

Available modes:

• auto: prefer BufferPool staging plus batch_put_from for non-tensor payloads and fall back to regular store.put when that path is unavailable;

• copy: force the regular store.put path;

• zero_copy: require payloads to be explicit tensor_object_buffer instances; non-tensor structured payloads are rejected.

Partial reads

Read narrowing happens on top of read_spec(ref):

• select_members([...]) keeps only selected members;

• slice_member(name, axis=0, start=..., end=...) slices one ndarray member;

• materialize(spec) returns newly materialized objects.

spec = (
    transfer.read_spec(ref)
    .select_members(["tokens"])
    .slice_member("tokens", axis=0, start=2, end=5)
)
result = transfer.materialize(spec)

selected_tokens = result.objects["tokens"]

Current scope:

• byte members support full-member reads;

• ndarray members support full reads and sliced reads;

• full read is the default read_spec(ref) case.

Reusing caller-owned destinations

Use materialize_into() when the caller already owns the destination ndarray buffers and wants Mooncake to fill them directly.

destination = np.empty((3, 4), dtype=np.int32)
spec = (
    transfer.read_spec(ref)
    .select_members(["tokens"])
    .slice_member("tokens", axis=0, start=2, end=5)
)
result = transfer.materialize_into(spec, {"tokens": destination})

assert result.objects["tokens"] is destination

materialize_into() is only for members whose destination layout is already known to the caller. For byte members or default object reconstruction, use materialize().

Generic bundle fallback

If the caller does not need structured member semantics, the same helper also supports raw named bundles:

• put_bundle(...)

• remove_bundle(...)

Use the bundle path when the object is just a manifest plus named payloads, and use the structured object path when callers want member selection, slicing, and ndarray-aware materialization.

Zero-Copy API (Advanced Performance)

For maximum performance, especially with RDMA networks, use the zero-copy API. This allows direct memory access without intermediate copies.

Memory Registration

⚠️ Important: register_buffer is required for zero-copy RDMA operations. Without proper buffer registration, undefined behavior and memory corruption may occur.

Zero-copy operations require registered memory buffers. For repeated reads and writes, prefer the Python BufferPool helper described below so leases come from the store’s setup-time local buffer instead of registering and unregistering memory for every operation.

register_buffer()

Register a memory buffer for direct RDMA access.

unregister_buffer()

Unregister a previously registered buffer.

Click to expand: Buffer registration example

import numpy as np
from mooncake.store import MooncakeDistributedStore

# Initialize store
store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Create a large buffer
buffer = np.zeros(100 * 1024 * 1024, dtype=np.uint8)  # 100MB buffer

# Register the buffer for zero-copy operations
buffer_ptr = buffer.ctypes.data
result = store.register_buffer(buffer_ptr, buffer.nbytes)
if result != 0:
    print(f"Failed to register buffer: {result}")
    raise RuntimeError(f"Failed to register buffer: {result}")
print("Buffer registered successfully.")
store.unregister_buffer(buffer_ptr)

BufferPool Helper

BufferPool leases scratch buffers from the store’s setup-time local buffer for repeated zero-copy operations. It is useful when a caller repeatedly needs temporary memory, for example as the destination buffer for get_into() or get_into_ranges().

from mooncake.buffer_pool import BufferPool

pool = BufferPool(store)

with pool.buffer(1024 * 1024) as lease:
    n = store.get_into("my_key", lease.ptr, lease.size)
    view = lease.buffer[:n]
    # Consume view directly, or wrap it with np.frombuffer(view, dtype=...).
    # Copy only if the data must outlive the lease: data = bytes(view)

pool.close()

acquire(size) and buffer(size) return a lease object. A lease exposes:

• ptr: the local-buffer address to pass to zero-copy APIs.

• size: the requested logical size.

• buffer: a Python memoryview over the logical requested size.

• release(): returns the local-buffer allocation to the store allocator.

Behavior and lifecycle rules:

• Leases prefer the store local buffer shared with internal Store staging paths.

• If local-buffer allocation is temporarily exhausted, BufferPool can allocate and register a short-lived overflow buffer; the overflow buffer is unregistered when the lease is released.

• max_regions can limit the number of concurrently active external leases.

• max_bytes bounds total active local-buffer and overflow leases; the default allows one local-buffer-sized overflow burst.

• acquire(size, block=False) raises when both local and overflow capacity are exhausted instead of waiting.

• acquire(size, timeout=...) can wait for another lease to be released.

• Do not keep lease.ptr or a memoryview after releasing the lease.

• release() fails while exported views are alive. Delete those views first, then release.

• close() fails if leases are still active. Release all leases before closing the pool.

Legacy code may still import RegisteredBufferPool, but new examples should prefer mooncake.buffer_pool.BufferPool.

---

Zero-Copy Operations

Complete Zero-Copy Workflow

⚠️ Critical: Always register buffers before zero-copy operations. Failure to register buffers will cause undefined behavior and potential memory corruption.

Here’s a complete example showing the full zero-copy workflow with proper buffer management:

Click to expand: Complete zero-copy workflow example

import numpy as np
from mooncake.store import MooncakeDistributedStore

# Initialize store with RDMA protocol for maximum performance
store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 16*1024*1024, "tcp", "", "localhost:50051")

# Create data to store
original_data = np.random.randn(1000, 1000).astype(np.float32)
buffer_ptr = original_data.ctypes.data
size = original_data.nbytes

# Step 1: Register the buffer
result = store.register_buffer(buffer_ptr, size)
if result != 0:
    raise RuntimeError(f"Failed to register buffer: {result}")

# Step 2: Zero-copy store
result = store.put_from("large_tensor", buffer_ptr, size)
if result == 0:
    print(f"Successfully stored {size} bytes with zero-copy")
else:
    raise RuntimeError(f"Store failed with code: {result}")

# Step 3: Pre-allocate buffer for retrieval
retrieved_data = np.empty((1000, 1000), dtype=np.float32)
recv_buffer_ptr = retrieved_data.ctypes.data
recv_size = retrieved_data.nbytes

# Step 4: Register receive buffer
result = store.register_buffer(recv_buffer_ptr, recv_size)
if result != 0:
    raise RuntimeError(f"Failed to register receive buffer: {result}")

# Step 5: Zero-copy retrieval
bytes_read = store.get_into("large_tensor", recv_buffer_ptr, recv_size)
if bytes_read > 0:
    print(f"Successfully retrieved {bytes_read} bytes with zero-copy")
    # Verify the data
    print(f"Data matches: {np.array_equal(original_data, retrieved_data)}")
else:
    raise RuntimeError(f"Retrieval failed with code: {bytes_read}")

# Step 6: Clean up - unregister both buffers
store.unregister_buffer(buffer_ptr)
store.unregister_buffer(recv_buffer_ptr)
store.close()

put_from()

Store data directly from a registered buffer (zero-copy).

def put_from(self, key: str, buffer_ptr: int, size: int, config=None) -> int

Parameters:

• key: Object identifier

• buffer_ptr: Memory address (from ctypes.data or similar)

• size: Number of bytes to store

• config: Optional replication configuration

get_into()

Retrieve data directly into a registered buffer (zero-copy).

def get_into(self, key: str, buffer_ptr: int, size: int) -> int

Parameters:

• key: Object identifier to retrieve

• buffer_ptr: Memory address of pre-allocated buffer

• size: Size of the buffer (must be >= object size)

Returns: Number of bytes read, or negative on error

get_into_ranges()

Retrieve multiple byte ranges from multiple objects into registered buffers (zero-copy).

def get_into_ranges(self, buffer_ptrs: List[int], all_keys: List[List[str]], all_dst_offsets: List[List[List[int]]], all_src_offsets: List[List[List[int]]], all_sizes: List[List[List[int]]]) -> List[List[List[int]]]

This API is buffer-major and supports multiple fragments per key.

Think of the input shape as:

• buffer_ptrs[i]: the i-th destination buffer

• all_keys[i][j]: the j-th key that writes into buffer i

• all_dst_offsets[i][j][k]: destination offset of fragment k for key j in buffer i

• all_src_offsets[i][j][k]: source offset of fragment k inside key j for buffer i

• all_sizes[i][j][k]: byte size of fragment k

For each triple (i, j, k), Mooncake reads the source range [all_src_offsets[i][j][k], all_src_offsets[i][j][k] + all_sizes[i][j][k]) from object all_keys[i][j], then writes it into destination buffer buffer_ptrs[i] at offset all_dst_offsets[i][j][k].

This lets one buffer gather interleaved fragments from multiple keys, and lets one key contribute multiple disjoint fragments to the same buffer in a single call.

Parameters:

• buffer_ptrs: Memory addresses of pre-allocated destination buffers. Each buffer must resolve to Store-managed registered memory, either from BufferPool/the setup-time local buffer or from an explicit register_buffer() call.

• all_keys: For each buffer, the ordered list of source object keys to read from.

• all_dst_offsets: For each buffer and key, the destination offsets of that key’s fragments.

• all_src_offsets: For each buffer and key, the source offsets of that key’s fragments inside the object.

• all_sizes: For each buffer and key, the byte lengths of that key’s fragments.

Shape rules:

• len(buffer_ptrs) == len(all_keys) == len(all_dst_offsets) == len(all_src_offsets) == len(all_sizes)

• For each buffer i, len(all_keys[i]) == len(all_dst_offsets[i]) == len(all_src_offsets[i]) == len(all_sizes[i])

• For each (buffer i, key j), len(all_dst_offsets[i][j]) == len(all_src_offsets[i][j]) == len(all_sizes[i][j])

If a top-level shape or per-key fragment shape does not match, the corresponding result entries are negative error codes.

Returns: A nested list of per-buffer, per-key, per-fragment results. results[i][j][k] is the number of bytes read for fragment k, or a negative value on error.

A successful call can still contain per-fragment failures. For example, if one key is missing but another key in the same buffer is valid, the missing key’s fragment result will be negative while the valid fragment can still succeed.

Typical scenarios:

• Partial read from one object: You only need a slice of a large value, such as a header, metadata block, or a small subrange of a tensor shard. In this case, use one buffer, one key, and one or more fragments under that key.

• Stitch multiple fragments from one object into one buffer: You need several non-contiguous ranges from the same object and want to pack them into one destination buffer. In this case, keep a single key entry and place multiple fragments under that key.

• Stitch data from multiple objects into one buffer: You want to assemble one logical payload from several keys. In this case, use one destination buffer and list multiple keys under that buffer, with each key contributing one or more fragments.

• Fill multiple output buffers in one call: You have several destination buffers, each with its own read plan. In this case, each top-level entry in buffer_ptrs and the parallel nested arrays describes one independent destination buffer.

How to use it for partial reads: If you only want part of an object, do not call get_into() with the full object buffer size. Instead:

1. Allocate and register a destination buffer sized for the bytes you actually want to materialize.

2. Put that buffer pointer into buffer_ptrs.

3. Put the source key into all_keys.

4. Set all_src_offsets to the start offsets of the object ranges you want.

5. Set all_sizes to the lengths of those ranges.

6. Set all_dst_offsets to where those ranges should land in your destination buffer.

A useful way to think about the arguments is:

• buffer_ptrs answers where does the data land

• all_keys answers which object does it come from

• all_src_offsets and all_sizes answer which bytes should be read

• all_dst_offsets answers where each fragment should be placed in the destination buffer

If you are extracting a single contiguous slice from one object, the minimal shape is:

results = store.get_into_ranges(
    [buffer_ptr],
    [["my_key"]],
    [[[0]]],
    [[[src_offset]]],
    [[[size]]],
)

This means:

• one destination buffer

• one source key for that buffer

• one fragment for that key

• read size bytes from my_key[src_offset:src_offset + size]

• write them into buffer_ptr[0:size]

If you want to read several disjoint ranges from the same object and pack them together, keep the same key and add more fragments under it. For example:

results = store.get_into_ranges(
    [buffer_ptr],
    [["my_key"]],
    [[[0, 16, 40]]],
    [[[128, 4096, 8192]]],
    [[[8, 12, 4]]],
)

This reads three fragments from my_key and places them into the same destination buffer at offsets 0, 16, and 40. This pattern is useful when you want to assemble only the needed pieces of a large object without reading the whole value.

If you want to assemble one output buffer from multiple objects, keep one top-level buffer entry and add multiple keys under it. Each key can still contribute one or more fragments. For example, you might put a header from meta_key at the front of the buffer, then place a payload slice from data_key after it.

Usage example:

import ctypes

buffer_size = 32
buffer0 = (ctypes.c_ubyte * buffer_size)()
buffer1 = (ctypes.c_ubyte * buffer_size)()
buffer_ptr0 = ctypes.addressof(buffer0)
buffer_ptr1 = ctypes.addressof(buffer1)

store.register_buffer(buffer_ptr0, buffer_size)
store.register_buffer(buffer_ptr1, buffer_size)

# Buffer 0 reads:
# - from key1: two fragments -> src[1:5] -> dst[0:4], src[30:33] -> dst[20:23]
# - from key2: one fragment  -> src[2:7] -> dst[8:13]
# Buffer 1 reads:
# - from key2: one fragment  -> src[0:6] -> dst[4:10]
# - from key1: one fragment  -> src[10:14] -> dst[16:20]
results = store.get_into_ranges(
    [buffer_ptr0, buffer_ptr1],
    [["key1", "key2"], ["key2", "key1"]],
    [[[0, 20], [8]], [[4], [16]]],
    [[[1, 30], [2]], [[0], [10]]],
    [[[4, 3], [5]], [[6], [4]]],
)

# results == [
#   [[4, 3], [5]],
#   [[6], [4]],
# ]

In the example above:

• results[0][0][0] == 4: buffer 0, key 0 ("key1"), fragment 0 succeeded with 4 bytes

• results[0][0][1] == 3: buffer 0, key 0 ("key1"), fragment 1 succeeded with 3 bytes

• results[0][1][0] == 5: buffer 0, key 1 ("key2"), fragment 0 succeeded with 5 bytes

Common pitfalls:

• Do not flatten all fragments for a buffer into one list. Fragments must be grouped under their corresponding key.

• all_dst_offsets, all_src_offsets, and all_sizes are 3D, but all_keys is 2D.

• Buffer overflow is checked against the registered destination buffer size.

• Source overflow is checked against the source object’s size.

• Full-object get_into() and ranged get_into_ranges() are different APIs; use get_into() when you want the whole object into one buffer.

Current limitation: true ranged items currently require the selected source replica to be memory-backed. Whole-object reads still follow the normal full-read path, but partial reads through get_into_ranges() do not support non-memory replicas.

---

ReplicateConfig Configuration

The ReplicateConfig class allows you to control data replication behavior when storing objects in Mooncake Store. This configuration is essential for ensuring data reliability, performance optimization, and storage placement control.

Class Definition

from mooncake.store import ReplicateConfig

# Create a configuration instance
config = ReplicateConfig()

Properties

replica_num

Type: int Default: 1 Description: Specifies the number of memory replicas to create for the stored object.

config = ReplicateConfig()
config.replica_num = 3  # Store 3 memory replicas

nof_replica_num

Type: int Default: 0 Description: Specifies the number of replicas to create in the configured NVMe-oF SSD pool.

config = ReplicateConfig()
config.replica_num = 1
config.nof_replica_num = 1

dfs_replica_num

Type: int Default: 0 Status: Work in progress; development and evaluation only. Description: Requests an additional replica in the configured shared distributed filesystem. The supported values are currently 0 and 1. When set to 1, replica_num must be at least 1, so DFS-only placement is not supported. DFS replicas currently support only the default tenant.

config = ReplicateConfig()
config.replica_num = 1
config.dfs_replica_num = 1

Writes that request a DFS replica return success after the DFS WriteAt operation completes, but without an additional fsync durability guarantee. The master and client DFS backends must be enabled and configured with the same absolute shared-root path and shard layout. See the DFS deployment documentation for the required environment variables and current limitations.

For a same-size upsert, if either the existing object or the new request has a DFS replica, the requested memory, NoF, and DFS replica counts must match the existing topology. A different-size update allocates a new topology.

soft_pin_action

Type: SoftPinAction Default: SoftPinAction.PRESERVE Description: Controls the soft-pin transition committed when the first replica becomes readable. PRESERVE keeps an existing deadline during Upsert, ENABLE starts a fixed soft-pin lifetime, and DISABLE removes it. Reads do not extend the lifetime.

from mooncake.store import ReplicateConfig, SoftPinAction

config = ReplicateConfig()
config.soft_pin_action = SoftPinAction.ENABLE
config.soft_pin_ttl_ms = 60_000  # Optional; omitted uses the Master default

soft_pin_ttl_ms is valid only with ENABLE. The Master rejects TTLs above max_kv_soft_pin_ttl; a value of zero commits the object as ordinary cache. Soft-pin state is not persisted in snapshots or the HA OpLog. Restored objects therefore become ordinary cache after recovery or Standby promotion.

with_hard_pin

Type: bool Default: False Description: Enables hard pinning for the stored object. Hard pinned objects will not be evicted. This grants user to manually control the life time of stored objects.

config = ReplicateConfig()
config.with_hard_pin = True  # Keep this object in memory that will not be evicted

preferred_segment

Type: str Default: "" (empty string) Description: Specifies a preferred segment (node) for data allocation. This is typically the hostname:port of a target server.

config = ReplicateConfig()

# Preferred replica location ("host:port")
config.preferred_segment = "localhost:12345"     # pin to a specific machine

# Alternatively, pin to the local host
config.preferred_segment = self.get_hostname()

# Optional: speed up local transfers
#   export MC_STORE_MEMCPY=1

prefer_alloc_in_same_node

Type: bool Default: False Description: Enables host-aware local-first allocation for this request, using the writer host identity and the normal ordered remote fallback. This can be used with direct multi-buffer writes and tensor write APIs to avoid staging when the selected segment is local and local memcpy is enabled. It does not support disk segments, and the replica_num can only be set to 1. Tensor APIs keep their default staging behavior unless this flag is explicitly enabled.

config = ReplicateConfig()
config.prefer_alloc_in_same_node = True

group_ids

Type: List[str] | None Default: None Description: Optionally assigns object metadata to routing groups during writes. When this field is unset, Mooncake Store preserves the default ungrouped behavior. When it is set, each group ID maps to the object at the same position in the write request. Empty string ("") explicitly stores that object as ungrouped.

For batch write APIs, the number of group IDs must match the number of keys:

config = ReplicateConfig()
config.group_ids = ["session-a", "", "session-b"]

store.put_batch(
    ["key-a", "key-b", "key-c"],
    [b"value-a", b"value-b", b"value-c"],
    config,
)

For a single-object write, provide one group ID:

config = ReplicateConfig()
config.group_ids = ["session-a"]

store.put("key-a", b"value-a", config)

---

Model Weight Snapshot API

Heterogeneous model-weight snapshots use the manifest-backed Reshard API. The framework adapter owns model semantics and exports a complete source placement plus live runtime bindings. Mooncake Store persists the resulting payloads and the immutable stored manifest.

from mooncake.reshard.weight.store import WeightStore

weight_store = WeightStore(store)
session = weight_store.begin_weight_snapshot(descriptor, adapter)
session.write_tensor(tensor_id, tensor)
manifest = session.commit()

MooncakeDistributedStore.begin_weight_snapshot(descriptor, adapter) provides the same session for callers that already hold the native Store object.

write_tensor() validates the adapter-selected source fragments against the session placement and runtime bindings. commit() publishes one StoredWeightManifest after complete durable coverage. Restore uses WeightStore.load_manifest(), plan_load(), and load() with the target placement and runtime binding manifests.

Breaking Change and Migration

This release removes the public *_with_parallelism API family and the associated ParallelAxis, TensorParallelism, and ReadTarget helper types. Applications that create heterogeneous model-weight snapshots migrate their write path to begin_weight_snapshot(), write_tensor(), and commit(). The writer creates manifest-managed payload fragments and one StoredWeightManifest; it does not create ordinary Store tensor objects.

Applications restore a snapshot through load_manifest(), plan_load(), and load() with the target placement and runtime binding manifests. The existing single-axis TP APIs named *_with_tp remain separate compatibility APIs.

When commit() reports a manifest publication failure after Store records the commit decision, the writer remains open and preserves its payloads. Retry commit() on that writer to complete manifest publication.

---

Non-Zero-Copy API (Simple Usage)

For simpler use cases, use the standard API without memory registration:

Basic Operations

Click to expand: Non-zero-copy API examples

from mooncake.store import MooncakeDistributedStore

# Initialize (same as zero-copy)
store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Simple put/get (automatic memory management)
data = b"Hello, World!" * 1000  # ~13KB
store.put("message", data)

retrieved = store.get("message")
print(retrieved == data)  # True

# Batch operations
keys = ["key1", "key2", "key3"]
values = [b"value1", b"value2", b"value3"]

store.put_batch(keys, values)
retrieved = store.get_batch(keys)
print("Retrieved all keys successfully:", retrieved == values)

Performance Notes

Choose the appropriate API based on your use case:

Zero-copy API is beneficial when:

• Working with large data transfers

• RDMA network infrastructure is available and configured

• Direct memory access patterns fit your application design

Non-zero-copy API is suitable for:

• Development and prototyping phases

• Applications without specific performance requirements

Batch operations can improve throughput for:

• Multiple related operations performed together

• Scenarios where network round-trip reduction is beneficial

---

Topology & Devices

• Auto-discovery: Enabled by default for protocol="rdma" or protocol="efa" when rdma_devices is empty.

• Discovery controls:

  • MC_MS_AUTO_DISC=1 forces auto-discovery; then rdma_devices is ignored.

  • MC_MS_AUTO_DISC=0 disables auto-discovery; then rdma_devices is required for RDMA/EFA.

  • MC_MS_FILTERS restricts auto-discovery to a comma-separated whitelist of NIC names, e.g. MC_MS_FILTERS=mlx5_0,mlx5_2.

Examples:

# Auto-select with default settings
python - <<'PY'
from mooncake.store import MooncakeDistributedStore as S
s = S()
s.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "rdma", "", "localhost:50051")
PY

# Manual device list
unset MC_MS_AUTO_DISC
python - <<'PY'
from mooncake.store import MooncakeDistributedStore as S
s = S()
s.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "rdma", "mlx5_0,mlx5_1", "localhost:50051")
PY

# Auto-select with filters
export MC_MS_AUTO_DISC=1
export MC_MS_FILTERS=mlx5_0,mlx5_2
python - <<'PY'
from mooncake.store import MooncakeDistributedStore as S
s = S()
s.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "rdma", "", "localhost:50051")
PY

get_buffer Buffer Protocol

The get_buffer method returns a BufferHandle object that implements the Python buffer protocol:

Click to expand: Buffer protocol usage example

# Get buffer with buffer protocol support
buffer = store.get_buffer("large_object")
if buffer:
    # Access as numpy array without copy
    import numpy as np
    arr = np.array(buffer, copy=False)

    # Direct memory access
    ptr = buffer.ptr()  # Memory address
    size = buffer.size()  # Buffer size in bytes

    # Use with other libraries that accept buffer protocol
    print(f"Buffer size: {len(buffer)} bytes")

    # The buffer is automatically freed

---

Full API Reference

Class: MooncakeDistributedStore

The main class for interacting with Mooncake Store.

Constructor

store = MooncakeDistributedStore()

Creates a new store instance. No parameters required.

---

setup()

Initialize distributed resources and establish network connections.

def setup(
    self,
    local_hostname: str,
    metadata_server: str,
    global_segment_size: int,
    local_buffer_size: int,
    protocol: str,
    rdma_devices: str,
    master_server_addr: str,
    engine: Optional[TransferEngine] = None,
    enable_ssd_offload: bool = False,
    ssd_offload_path: str = "",
    tenant_id: str = "default",
    enable_client_http_server: bool = False,
    client_http_port: int = 9300,
) -> int

The positional overload requires every argument through master_server_addr. To use defaults for those fields, pass a configuration dictionary instead:

def setup(self, config: Dict[str, object]) -> int

The dictionary overload requires local_hostname and metadata_server. Its other keys are optional; the defaults are 16777216 (16 MiB) for both global_segment_size and local_buffer_size, "tcp" for protocol, an empty string for rdma_devices, and "127.0.0.1:50051" for master_server_addr. It also accepts ipc_socket_path and the optional configuration fields listed below. The engine argument is available only in the positional overload.

Parameters:

• local_hostname (str): Required. Local hostname and port (e.g., “localhost” or “localhost:12345”)

• metadata_server (str): Required. Metadata connection string, e.g. "P2PHANDSHAKE" or "http://localhost:8080/metadata".

• global_segment_size (int): Required by the positional overload. Memory segment size in bytes for mounting.

• local_buffer_size (int): Required by the positional overload. Local buffer size in bytes.

• protocol (str): Required by the positional overload. Network protocol, usually "tcp", "rdma", "efa", "cxl", or "ascend" depending on the build.

• rdma_devices (str): Required by the positional overload. RDMA/EFA device name(s), e.g. "mlx5_0" or "mlx5_0,mlx5_1". Leave empty to auto-discover NICs unless MC_MS_AUTO_DISC=0; always empty for TCP.

• master_server_addr (str): Required by the positional overload. Master server address (e.g., “localhost:50051”)

• engine (Optional[TransferEngine]): Existing Transfer Engine instance to reuse. Defaults to None.

• enable_ssd_offload (bool): Initialize client-side FileStorage. With a normal file backend this enables SSD offload; with MOONCAKE_OFFLOAD_STORAGE_BACKEND_DESCRIPTOR=distributed_storage_backend, it initializes the DFS backend and is required for DFS reads and writes. Defaults to False.

• ssd_offload_path (str): FileStorage directory. When provided, it overrides MOONCAKE_OFFLOAD_FILE_STORAGE_PATH. With the distributed backend, DFS shard data is stored under MOONCAKE_DFS_ROOT_DIR, but this separate directory is still validated during FileStorage initialization.

• tenant_id (str): Tenant namespace for object keys. Defaults to "default".

• enable_client_http_server (bool): Enable the client-local /health, /metrics, /metrics/summary, and /version HTTP endpoints. Defaults to False.

• client_http_port (int): Port for the client-local HTTP endpoints. Defaults to 9300.

Store segment pinned memory: CUDA-enabled builds can register Store-managed host segments as pinned memory when MC_STORE_PIN_MEMORY_MAX_BYTES is set to a positive process-wide quota; unset, empty, 0, or invalid values disable it. The scope is limited to host Store segments allocated by setup() (global_segment_size) and allocateAndMountSegment(); it excludes file-backed mountSegment() mappings, CXL/device segments, local_buffer_size, user buffers, dummy-client shared memory, and temporary staging buffers. If the quota is exhausted or CUDA registration fails, Mooncake continues with pageable Store segment memory.

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

Click to expand: Setup examples for TCP and RDMA

# TCP initialization
store.setup("localhost", "http://localhost:8080/metadata", 1024*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# RDMA auto-detect
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "rdma", "", "localhost:50051")

# RDMA with explicit device list
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "rdma", "mlx5_0,mlx5_1", "localhost:50051")

---

setup_dummy()

Initialize the store with a dummy client for testing purposes.

def setup_dummy(self, mem_pool_size: int, local_buffer_size: int, server_address: str) -> int

Parameters:

• mem_pool_size (int): Memory pool size in bytes

• local_buffer_size (int): Local buffer size in bytes

• server_address (str): Server address in format “hostname:port”

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

# Initialize with dummy client
store.setup_dummy(1024*1024*256, 1024*1024*64, "localhost:8080")

Dummy clients do not own Store segments. They use a local shared-memory buffer that is mapped by a real client process at server_address. Tensor APIs that stage through this SHM buffer are supported, including tensor put/get, *_tensor_from, *_tensor_into, tensor upsert/pub, and the single-axis TP wrappers. Model-weight snapshots use the explicit snapshot API described above.

The real client owns the SHM buffer allocator. This keeps tensor writes and regular object writes from allocating overlapping offsets when they run concurrently through the same dummy client. Writes staged through the dummy client’s local SHM buffer keep their allocation alive until completion through the real-side active buffer handle and dummy-side RAII release path.

Full materialized reconstruction reads for writer-sharded or reconstructed parallel tensors are still conservative for dummy clients. Use the corresponding *_into APIs, or read stored shards directly, when using dummy clients.

---

put()

Store binary data in the distributed storage.

def put(self, key: str, value: bytes, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Unique object identifier

• value (bytes): Binary data to store

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

Click to expand: Put operation examples

# Simple put
store.put("my_key", b"Hello, World!")

# Put with replication config
config = ReplicateConfig()
config.replica_num = 2
store.put("important_data", b"Critical information", config)

---

get()

Retrieve binary data from distributed storage.

def get(self, key: str) -> bytes

Parameters:

• key (str): Object identifier to retrieve

Returns:

• bytes: Retrieved binary data

Raises:

• Returns empty bytes if key doesn’t exist

Example:

Click to expand: Get operation example

data = store.get("my_key")
if data:
    print(f"Retrieved: {data.decode()}")
else:
    print("Key not found")

---

put_batch()

Store multiple objects in a single batch operation.

def put_batch(self, keys: List[str], values: List[bytes], config: ReplicateConfig = None) -> int

Parameters:

• keys (List[str]): List of object identifiers

• values (List[bytes]): List of binary data to store

• config (ReplicateConfig, optional): Replication configuration for all objects

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

Click to expand: Batch put example

keys = ["key1", "key2", "key3"]
values = [b"value1", b"value2", b"value3"]
result = store.put_batch(keys, values)

---

upsert()

Insert a new object if the key does not exist, or update the existing object in place when possible. They use the same replication configuration model as put().

Upsert binary data in the distributed storage.

def upsert(self, key: str, value: bytes, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Unique object identifier

• value (bytes): Binary data to insert or update

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

config = ReplicateConfig()
config.replica_num = 2

rc = store.upsert("weights", b"new-bytes", config)
if rc == 0:
    print("Upsert succeeded")

upsert_from()

Upsert object data directly from a pre-allocated buffer (zero-copy).

def upsert_from(self, key: str, buffer_ptr: int, size: int, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Object identifier

• buffer_ptr (int): Memory address of the source buffer

• size (int): Number of bytes to insert or update

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This is the zero-copy counterpart of upsert(). As with put_from(), register the buffer before issuing the request.

batch_upsert_from()

Upsert multiple objects directly from pre-allocated buffers.

def batch_upsert_from(self, keys: List[str], buffer_ptrs: List[int], sizes: List[int],
                      config: ReplicateConfig = None) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• buffer_ptrs (List[int]): List of source buffer addresses

• sizes (List[int]): List of byte lengths for each buffer

• config (ReplicateConfig, optional): Replication configuration shared by all objects

Returns:

• List[int]: List of status codes for each upsert

upsert_parts()

Upsert data from multiple buffer parts as a single object (insert or update).

def upsert_parts(self, key: str, *parts, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Object identifier

• *parts: Variable number of bytes-like objects to concatenate

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

part1 = b"Hello, "
part2 = b"World!"
result = store.upsert_parts("greeting", part1, part2)

upsert_batch()

Upsert multiple objects in a single batch operation.

def upsert_batch(self, keys: List[str], values: List[bytes], config: ReplicateConfig = None) -> int

Parameters:

• keys (List[str]): List of object identifiers

• values (List[bytes]): List of binary data to insert or update

• config (ReplicateConfig, optional): Replication configuration for all objects

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

keys = ["key1", "key2", "key3"]
values = [b"value1", b"value2", b"value3"]
result = store.upsert_batch(keys, values)

---

get_batch()

Retrieve multiple objects in a single batch operation.

def get_batch(self, keys: List[str]) -> List[bytes]

Parameters:

• keys (List[str]): List of object identifiers to retrieve

Returns:

• List[bytes]: List of retrieved binary data

Example:

Click to expand: Batch get example

keys = ["key1", "key2", "key3"]
values = store.get_batch(keys)
for key, value in zip(keys, values):
    print(f"{key}: {len(value)} bytes")

---

remove()

Delete an object from the storage system.

def remove(self, key: str) -> int

Parameters:

• key (str): Object identifier to remove

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

result = store.remove("my_key")
if result == 0:
    print("Successfully removed")

---

remove_by_regex()

Remove objects from the storage system whose keys match a regular expression.

def remove_by_regex(self, regex: str) -> int

Parameters:

• regex (str): The regular expression to match against object keys.

Returns:

• int: The number of objects removed, or a negative value on error.

Example:

# Remove all keys starting with "user_session_"
count = store.remove_by_regex("^user_session_.*")
if count >= 0:
    print(f"Removed {count} objects")

---

remove_all()

Remove all objects from the storage system.

def remove_all(self) -> int

Returns:

• int: Number of objects removed, or -1 on error

Example:

count = store.remove_all()
print(f"Removed {count} objects")

---

batch_remove()

Remove multiple objects by their keys in a single batch operation.

def batch_remove(self, keys: List[str], force: bool = False) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers to remove

• force (bool): If True, skip lease and replication task checks (default: False)

Returns:

• List[int]: List of status codes for each key (0 = success, negative = error code)

Example:

# Remove multiple keys in one batch
keys = ["key1", "key2", "key3", "key4", "key5"]
results = store.batch_remove(keys)

# Check results
for key, result in zip(keys, results):
    if result == 0:
        print(f"✓ {key} removed successfully")
    else:
        print(f"✗ {key} failed with error code: {result}")

# Force remove (bypass lease checks)
results = store.batch_remove(keys, force=True)

---

is_exist()

Check if an object exists in the storage system.

def is_exist(self, key: str) -> int

Parameters:

• key (str): Object identifier to check

Returns:

• int:

  • 1: Object exists

  • 0: Object doesn’t exist

  • -1: Error occurred

Example:

exists = store.is_exist("my_key")
if exists == 1:
    print("Object exists")
elif exists == 0:
    print("Object not found")
else:
    print("Error checking existence")

---

batch_is_exist()

Check existence of multiple objects in a single batch operation.

def batch_is_exist(self, keys: List[str]) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers to check

Returns:

• List[int]: List of existence results (1=exists, 0=not exists, -1=error)

Example:

keys = ["key1", "key2", "key3"]
results = store.batch_is_exist(keys)
for key, exists in zip(keys, results):
    status = "exists" if exists == 1 else "not found" if exists == 0 else "error"
    print(f"{key}: {status}")

---

get_size()

Get the size of a stored object in bytes.

def get_size(self, key: str) -> int

Parameters:

• key (str): Object identifier

Returns:

• int: Size in bytes, or negative value on error

Example:

size = store.get_size("my_key")
if size >= 0:
    print(f"Object size: {size} bytes")
else:
    print("Error getting size or object not found")

---

get_buffer()

Get object data as a buffer that implements Python’s buffer protocol.

def get_buffer(self, key: str) -> BufferHandle

Parameters:

• key (str): Object identifier

Returns:

• BufferHandle: Buffer object or None if not found

Example:

buffer = store.get_buffer("large_object")
if buffer:
    print(f"Buffer size: {buffer.size()} bytes")
    # Use with numpy without copying
    import numpy as np
    arr = np.array(buffer, copy=False)

---

put_parts()

Store data from multiple buffer parts as a single object.

def put_parts(self, key: str, *parts, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Object identifier

• *parts: Variable number of bytes-like objects to concatenate

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

part1 = b"Hello, "
part2 = b"World!"
part3 = b" From Mooncake"
result = store.put_parts("greeting", part1, part2, part3)

---

batch_get_buffer()

Get multiple objects as buffers that implement Python’s buffer protocol.

def batch_get_buffer(self, keys: List[str]) -> List[BufferHandle]

Parameters:

• keys (List[str]): List of object identifiers to retrieve

Returns:

• List[BufferHandle]: List of buffer objects, with None for keys not found

Note: This function is supported for dummy clients through the real client-owned shared-memory staging buffer.

Example:

buffers = store.batch_get_buffer(["key1", "key2", "key3"])
for i, buffer in enumerate(buffers):
    if buffer:
        print(f"Buffer {i} size: {buffer.size()} bytes")

---

alloc_from_mem_pool()

Allocate memory from the memory pool.

def alloc_from_mem_pool(self, size: int) -> int

Parameters:

• size (int): Size of memory to allocate in bytes

Returns:

• int: Memory address as integer, or 0 on failure

---

init_all()

Initialize all resources with specified protocol and device.

def init_all(self, protocol: str, device_name: str, mount_segment_size: int = 16777216) -> int

Parameters:

• protocol (str): Network protocol - “tcp” or “rdma”

• device_name (str): Device name for the protocol

• mount_segment_size (int): Memory segment size in bytes for mounting (default: 16MB = 16777216)

Returns:

• int: Status code (0 = success, non-zero = error code)

---

mount_segment()

Mount a local file or shared-memory region as one or more Mooncake store segments.

def mount_segment(
    self,
    path: str,
    size: int,
    offset: int = 0,
    protocol: str = "tcp",
    location: str = "",
) -> dict

Parameters:

• path (str): File or shared-memory path to map and mount.

• size (int): Number of bytes to mount.

• offset (int, optional): File offset in bytes. Defaults to 0.

• protocol (str, optional): Transfer protocol. Defaults to "tcp".

• location (str, optional): Device or locality hint. Defaults to an empty string.

Returns:

• dict: A result dictionary with:

  • ret (int): Status code (0 = success, non-zero = error code)

  • segment_ids (List[str]): Segment ids created by the mount operation

Example:

result = store.mount_segment(
    "/dev/shm/mooncake_segment",
    16 * 1024 * 1024,
    offset=0,
    protocol="tcp",
    location="",
)

if result["ret"] == 0:
    segment_ids = list(result["segment_ids"])
    print("Mounted segments:", segment_ids)
else:
    print("Mount failed:", result["ret"])

The corresponding HTTP endpoints are /api/mount_shm and /api/unmount_shm, but the HTTP API is intentionally narrower: it accepts a named shared memory object name instead of an arbitrary path.

---

unmount_segment()

Unmount one or more file or shared-memory segments by segment id.

def unmount_segment(
    self,
    segment_ids: List[str],
    grace_period_seconds: int = 0,
) -> int

Parameters:

• segment_ids (List[str]): Segment ids returned by mount_segment().

• grace_period_seconds (int, optional): Grace period before the segment is fully unmounted. Defaults to 0, which keeps the existing immediate unmount behavior. During a positive grace period, the segment remains readable but no longer accepts new allocations.

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

ret = store.unmount_segment(segment_ids, grace_period_seconds=30)
if ret != 0:
    print("Unmount failed:", ret)

---

allocate_and_mount_segment()

Allocate memory inside the store process and mount it as one or more Mooncake store segments.

def allocate_and_mount_segment(
    self,
    size: int,
    protocol: str = "tcp",
    location: str = "",
) -> dict

Parameters:

• size (int): Number of bytes requested. The allocated size may be rounded up for alignment.

• protocol (str, optional): Transfer protocol. Defaults to "tcp".

• location (str, optional): Device or locality hint. Defaults to an empty string.

Returns:

• dict: A result dictionary with:

  • ret (int): Status code (0 = success, non-zero = error code)

  • segment_ids (List[str]): Segment ids created by the mount operation

  • allocated_size (int): Actual allocated size in bytes

Example:

result = store.allocate_and_mount_segment(
    16 * 1024 * 1024,
    protocol="tcp",
    location="",
)

if result["ret"] == 0:
    segment_ids = list(result["segment_ids"])
    allocated_size = result["allocated_size"]

The corresponding HTTP endpoints are /api/mount and /api/unmount.

---

unmount_and_free_segment()

Unmount one or more internally allocated segments by segment id and free their local memory.

def unmount_and_free_segment(
    self,
    segment_ids: List[str],
    grace_period_seconds: int = 0,
) -> int

Parameters:

• segment_ids (List[str]): Segment ids returned by allocate_and_mount_segment().

• grace_period_seconds (int, optional): Grace period before the segment is fully unmounted and its local allocated memory is released. Defaults to 0, which keeps the existing immediate unmount-and-free behavior. During a positive grace period, the segment remains readable but no longer accepts new allocations.

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

ret = store.unmount_and_free_segment(segment_ids, grace_period_seconds=30)
if ret != 0:
    print("Unmount and free failed:", ret)

---

get_hostname()

Get the hostname of the current store instance.

def get_hostname(self) -> str

Returns:

• str: Hostname and port of this store instance

Example:

hostname = store.get_hostname()
print(f"Store running on: {hostname}")

---

get_replica_desc()

Get descriptors of replicas for a key.

def get_replica_desc(self, key: str) -> List[Replica::Descriptor]

Parameters:

• key (str): mooncake store key

Returns:

• List[Replica::Descriptor]: List of replica descriptors

Example:

descriptors = store.get_replica_desc("mooncake_key")
for desc in descriptors:
    print("Status:", desc.status)
    if desc.is_memory_replica():
        mem_desc = desc.get_memory_descriptor()
        print("Memory buffer desc:", mem_desc.buffer_descriptor)
    elif desc.is_disk_replica():
        disk_desc = desc.get_disk_descriptor()
        print("Disk path:", disk_desc.file_path, "Size:", disk_desc.object_size)

---

batch_get_replica_desc()

Get descriptors of replicas for a tuple of keys.

def batch_get_replica_desc(self, keys: List[str]) -> Dict[str, List[Replica::Descriptor]]

Parameters:

• keys (List[str]): List of mooncake store keys

Returns:

• Dict[str, List[Replica::Descriptor]]: Dictionary mapping keys to their list of replica descriptors

Example:

descriptors_map = store.batch_get_replica_desc(["key1", "key2"])
for key, desc_list in descriptors_map.items():
    print(f"Replicas for key: {key}")
    for desc in desc_list:
        if desc.is_memory_replica():
            mem_desc = desc.get_memory_descriptor()
            print("Memory buffer desc:", mem_desc.buffer_descriptor)
        elif desc.is_disk_replica():
            disk_desc = desc.get_disk_descriptor()
            print("Disk path:", disk_desc.file_path, "Size:", disk_desc.object_size)

---

create_copy_task()

Creates an asynchronous copy task to replicate an object to target segments.

def create_copy_task(self, key: str, targets: List[str]) -> Tuple[UUID, int]

Parameters:

• key (str): Object key to copy

• targets (List[str]): List of target segment names where replicas should be created

Returns:

• Tuple[UUID, int]: (task UUID, error code)

  • If successful: (task UUID, 0)

  • If failed: (UUID{0, 0}, error code)

Task lifecycle and failure behavior:

• New tasks start in TaskStatus.PENDING, move to TaskStatus.PROCESSING after a client picks them up, and finish as TaskStatus.SUCCESS or TaskStatus.FAILED.

• The task payload is executed by a storage client in the background; the client reports the final status back to the master automatically.

• Only allocation-pressure failures (NO_AVAILABLE_HANDLE) are retried automatically by the client, up to the master-side max_retry_attempts setting.

• Submission can fail immediately with errors such as TASK_PENDING_LIMIT_EXCEEDED when the master-side pending queue is full.

Example:

# Create an asynchronous copy task
task_id, error_code = store.create_copy_task("my_key", ["segment1", "segment2"])
if error_code == 0:
    print(f"Copy task created with ID: {task_id}")
    # Query task status later
    response, status = store.query_task(task_id)
    if status == 0:
        print(f"Task status: {response.status}")
else:
    print(f"Failed to create copy task: {error_code}")

---

create_move_task()

Creates an asynchronous move task to move an object from source segment to target segment.

def create_move_task(self, key: str, source: str, target: str) -> Tuple[UUID, int]

Parameters:

• key (str): Object key to move

• source (str): Source segment name where the replica currently exists

• target (str): Target segment name where the replica should be moved to

Returns:

• Tuple[UUID, int]: (task UUID, error code)

  • If successful: (task UUID, 0)

  • If failed: (UUID{0, 0}, error code)

Task lifecycle and failure behavior:

• Move tasks use the same state machine as copy tasks: PENDING -> PROCESSING -> SUCCESS/FAILED.

• Submission-time failures: If the object or source replica is already missing when create_move_task is called, the call returns an error code directly (e.g., OBJECT_NOT_FOUND or INVALID_PARAMS) and no task is created.

• Execution-time failures: If the object or source replica disappears after the task is successfully submitted, the task transitions to FAILED state. Only NO_AVAILABLE_HANDLE execution failures are retried automatically.

• Timeout and retry behavior is controlled on the master side rather than by the Python client API.

Example:

# Create an asynchronous move task
task_id, error_code = store.create_move_task("my_key", "old_segment", "new_segment")
if error_code == 0:
    print(f"Move task created with ID: {task_id}")
    # Query task status later
    response, status = store.query_task(task_id)
    if status == 0:
        print(f"Task status: {response.status}")
else:
    print(f"Failed to create move task: {error_code}")

---

query_task()

Queries the status of an asynchronous task (copy or move).

def query_task(self, task_id: UUID) -> Tuple[QueryTaskResponse | None, int]

Parameters:

• task_id (UUID): UUID of the task to query

Returns:

• Tuple[QueryTaskResponse | None, int]: (QueryTaskResponse if success, error code)

  • If successful: (QueryTaskResponse, 0)

  • If failed: (None, error code)

QueryTaskResponse includes:

• id: task UUID

• type: TaskType.REPLICA_COPY or TaskType.REPLICA_MOVE

• status: TaskStatus.PENDING, TaskStatus.PROCESSING, TaskStatus.SUCCESS, or TaskStatus.FAILED

• created_at_ms_epoch: creation timestamp in milliseconds

• last_updated_at_ms_epoch: last state-change timestamp in milliseconds

• assigned_client: UUID of the client currently assigned to the task

• message: completion or failure message

Typical query-time failures include:

• TASK_NOT_FOUND: the task ID does not exist or the finished task has already been pruned from the master’s in-memory history

Master-side task manager settings affecting task APIs:

• --max_total_finished_tasks: number of completed tasks retained for later query_task calls

• --max_total_pending_tasks: maximum queued tasks before submissions fail with TASK_PENDING_LIMIT_EXCEEDED

• --max_total_processing_tasks: cap on concurrently processing tasks

• --pending_task_timeout_sec: how long a task may stay in PENDING before being failed by the master (0 disables this timeout)

• --processing_task_timeout_sec: how long a task may stay in PROCESSING before being failed by the master (0 disables this timeout)

• --max_retry_attempts: retry budget used only for NO_AVAILABLE_HANDLE execution failures

Example:

from mooncake.store import MooncakeDistributedStore, TaskStatus
import time

# Initialize store
store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata",
            512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Submit multiple copy tasks
tasks = []
for key in ["key1", "key2", "key3"]:
    task_id, error = store.create_copy_task(key, ["segment1", "segment2"])
    if error == 0:
        tasks.append(task_id)
        print(f"Created copy task {task_id} for {key}")

# Monitor task progress
while tasks:
    completed = []
    for task_id in tasks:
        response, status = store.query_task(task_id)
        if status == 0 and response:
            if response.status == TaskStatus.SUCCESS:
                print(f"Task {task_id} succeeded")
                completed.append(task_id)
            elif response.status == TaskStatus.FAILED:
                print(f"Task {task_id} failed: {response.message}")
                completed.append(task_id)

    # Remove completed tasks
    tasks = [t for t in tasks if t not in completed]

    if tasks:
        time.sleep(1)  # Wait before next check

print("All tasks completed")
store.close()

---

close()

Clean up all resources and terminate connections.

def close(self) -> int

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

store.close()

---

put_from_with_metadata()

Store data directly from a registered buffer with metadata (zero-copy).

def put_from_with_metadata(self, key: str, buffer_ptr: int, metadata_buffer_ptr: int, size: int, metadata_size: int, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Object identifier

• buffer_ptr (int): Memory address of the main data buffer (from ctypes.data or similar)

• metadata_buffer_ptr (int): Memory address of the metadata buffer

• size (int): Number of bytes for the main data

• metadata_size (int): Number of bytes for the metadata

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This function is supported for dummy clients through the real client-owned shared-memory staging buffer.

Example:

import numpy as np

# Create data and metadata
data = np.random.randn(1000).astype(np.float32)
metadata = np.array([42, 100], dtype=np.int32)  # example metadata

# Register buffers
data_ptr = data.ctypes.data
metadata_ptr = metadata.ctypes.data
store.register_buffer(data_ptr, data.nbytes)
store.register_buffer(metadata_ptr, metadata.nbytes)

# Store with metadata
result = store.put_from_with_metadata("data_with_metadata", data_ptr, metadata_ptr,
                                     data.nbytes, metadata.nbytes)
if result == 0:
    print("Data with metadata stored successfully")

# Cleanup
store.unregister_buffer(data_ptr)
store.unregister_buffer(metadata_ptr)

---

pub_tensor()

Publish a PyTorch tensor with configurable replication settings.

def pub_tensor(self, key: str, tensor: torch.Tensor, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Unique object identifier

• tensor (torch.Tensor): PyTorch tensor to store

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This function requires torch to be installed and available in the environment.

Example:

import torch
from mooncake.store import ReplicateConfig, SoftPinAction

# Create a tensor
tensor = torch.randn(100, 100)

# Create replication config
config = ReplicateConfig()
config.replica_num = 3
config.soft_pin_action = SoftPinAction.ENABLE

# Publish tensor with replication settings
result = store.pub_tensor("my_tensor", tensor, config)
if result == 0:
    print("Tensor published successfully")

---

PyTorch Tensor Operations (Tensor Parallelism)

These methods provide direct support for storing and retrieving PyTorch tensors. They automatically handle serialization and metadata, and include built-in support for Tensor Parallelism (TP) by automatically splitting and reconstructing tensor shards.

⚠️ Note: These methods require torch to be installed and available in the environment.

put_tensor_with_tp()

Put a PyTorch tensor into the store, optionally splitting it into shards for tensor parallelism. The tensor is chunked immediately and stored as separate keys (e.g., key_tp_0, key_tp_1…).

def put_tensor_with_tp(self, key: str, tensor: torch.Tensor, tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> int

Parameters:

• key (str): Base identifier for the tensor.

• tensor (torch.Tensor): The PyTorch tensor to store.

• tp_rank (int): Current tensor parallel rank (default: 0). Note: The method splits and stores all chunks for all ranks regardless of this value.

• tp_size (int): Total tensor parallel size (default: 1). If > 1, the tensor is split into tp_size chunks.

• split_dim (int): The dimension to split the tensor along (default: 0).

Returns:

• int: Status code (0 = success, non-zero = error code).

pub_tensor_with_tp()

Publish a PyTorch tensor into the store with configurable replication settings, optionally splitting it into shards for tensor parallelism. The tensor is chunked immediately and stored as separate keys (e.g., key_tp_0, key_tp_1…).

def pub_tensor_with_tp(self, key: str, tensor: torch.Tensor, config: ReplicateConfig, tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> int

Parameters:

• key (str): Base identifier for the tensor.

• tensor (torch.Tensor): The PyTorch tensor to store.

• config (ReplicateConfig): Optional replication configuration.

• tp_rank (int): Current tensor parallel rank (default: 0). Note: The method splits and stores all chunks for all ranks regardless of this value.

• tp_size (int): Total tensor parallel size (default: 1). If > 1, the tensor is split into tp_size chunks.

• split_dim (int): The dimension to split the tensor along (default: 0).

Returns:

• int: Status code (0 = success, non-zero = error code).

get_tensor_with_tp()

Get a PyTorch tensor from the store, specifically retrieving the shard corresponding to the given Tensor Parallel rank.

def get_tensor_with_tp(self, key: str, tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> torch.Tensor

Parameters:

• key (str): Base identifier of the tensor.

• tp_rank (int): The tensor parallel rank to retrieve (default: 0). Fetches key key_tp_{rank} if tp_size > 1.

• tp_size (int): Total tensor parallel size (default: 1).

• split_dim (int): The dimension used during splitting (default: 0).

Returns:

• torch.Tensor: The retrieved tensor (or shard). Returns None if not found.

batch_put_tensor_with_tp()

Put a batch of PyTorch tensors into the store, splitting each into shards for tensor parallelism.

def batch_put_tensor_with_tp(self, base_keys: List[str], tensors_list: List[torch.Tensor], tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> List[int]

Parameters:

• base_keys (List[str]): List of base identifiers.

• tensors_list (List[torch.Tensor]): List of tensors to store.

• tp_rank (int): Current rank (default: 0).

• tp_size (int): Total TP size (default: 1).

• split_dim (int): Split dimension (default: 0).

Returns:

• List[int]: List of status codes for each tensor operation.

batch_pub_tensor_with_tp()

Publish a batch of PyTorch tensors into the store with configurable replication settings, splitting each into shards for tensor parallelism.

def batch_pub_tensor_with_tp(self, base_keys: List[str], tensors_list: List[torch.Tensor], config: ReplicateConfig, tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> List[int]

Parameters:

• base_keys (List[str]): List of base identifiers.

• tensors_list (List[torch.Tensor]): List of tensors to store.

• config (ReplicateConfig): Optional replication configuration.

• tp_rank (int): Current rank (default: 0).

• tp_size (int): Total tp size (default: 1).

• split_dim (int): Split dimension (default: 0).

Returns:

• List[int]: List of status codes for each tensor operation.

batch_get_tensor_with_tp()

Get a batch of PyTorch tensor shards from the store for a given Tensor Parallel rank.

def batch_get_tensor_with_tp(self, base_keys: List[str], tp_rank: int = 0, tp_size: int = 1) -> List[torch.Tensor]

Parameters:

• base_keys (List[str]): List of base identifiers.

• tp_rank (int): The tensor parallel rank to retrieve (default: 0).

• tp_size (int): Total tensor parallel size (default: 1).

Returns:

• List[torch.Tensor]: List of retrieved tensors (or shards). Contains None for missing keys.

---

put_tensor()

Put a PyTorch tensor into the store.

def put_tensor(self, key: str, tensor: torch.Tensor) -> int

Parameters:

• key (str): Object identifier

• tensor (torch.Tensor): The PyTorch tensor to store

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This function requires torch to be installed and available in the environment.

Example:

import torch
from mooncake.store import MooncakeDistributedStore

store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Store a tensor
tensor = torch.randn(100, 100)
result = store.put_tensor("my_tensor", tensor)
if result == 0:
    print("Tensor stored successfully")

---

get_tensor()

Get a PyTorch tensor from the store.

def get_tensor(self, key: str) -> torch.Tensor

Parameters:

• key (str): Object identifier to retrieve

Returns:

• torch.Tensor: The retrieved tensor. Returns None if not found.

Note: This function requires torch to be installed and available in the environment.

Example:

import torch
from mooncake.store import MooncakeDistributedStore

store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Store a tensor
tensor = torch.randn(100, 100)
store.put_tensor("my_tensor", tensor)

# Retrieve the tensor
retrieved_tensor = store.get_tensor("my_tensor")
if retrieved_tensor is not None:
    print(f"Retrieved tensor with shape: {retrieved_tensor.shape}")

---

batch_get_tensor()

Get a batch of PyTorch tensors from the store.

def batch_get_tensor(self, keys: List[str]) -> List[torch.Tensor]

Parameters:

• keys (List[str]): List of object identifiers to retrieve

Returns:

• List[torch.Tensor]: List of retrieved tensors. Contains None for missing keys.

Note: This function requires torch to be installed and available in the environment.

Example:

import torch
from mooncake.store import MooncakeDistributedStore

store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Store tensors
tensor1 = torch.randn(100, 100)
tensor2 = torch.randn(50, 50)
store.put_tensor("tensor1", tensor1)
store.put_tensor("tensor2", tensor2)

# Retrieve multiple tensors
tensors = store.batch_get_tensor(["tensor1", "tensor2", "nonexistent"])
for i, tensor in enumerate(tensors):
    if tensor is not None:
        print(f"Tensor {i} shape: {tensor.shape}")
    else:
        print(f"Tensor {i} not found")

---

batch_put_tensor()

Put a batch of PyTorch tensors into the store.

def batch_put_tensor(self, keys: List[str], tensors_list: List[torch.Tensor]) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• tensors_list (List[torch.Tensor]): List of tensors to store

Returns:

• List[int]: List of status codes for each tensor operation.

Note: This function requires torch to be installed and available in the environment.

Example:

import torch
from mooncake.store import MooncakeDistributedStore

store = MooncakeDistributedStore()
store.setup("localhost", "http://localhost:8080/metadata", 512*1024*1024, 128*1024*1024, "tcp", "", "localhost:50051")

# Create tensors
tensors = [torch.randn(100, 100), torch.randn(50, 50), torch.randn(25, 25)]
keys = ["tensor1", "tensor2", "tensor3"]

# Store multiple tensors
results = store.batch_put_tensor(keys, tensors)
for i, result in enumerate(results):
    if result == 0:
        print(f"Tensor {i} stored successfully")
    else:
        print(f"Tensor {i} failed to store with code: {result}")

batch_pub_tensor()

Pub a batch of PyTorch tensors into the store with configurable replication settings.

def batch_pub_tensor(self, keys: List[str], tensors_list: List[torch.Tensor], config: ReplicateConfig) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• tensors_list (List[torch.Tensor]): List of tensors to store

• config (ReplicateConfig): Optional replication configuration.

Returns:

• List[int]: List of status codes for each tensor operation.

Note: This function requires torch to be installed and available in the environment.

---

upsert_tensor()

Insert a tensor if its key is missing, or update the existing tensor if the key already exists. The current tensor upsert helpers use the default ReplicateConfig and therefore do not take a config parameter.

Upsert a PyTorch tensor into the store.

def upsert_tensor(self, key: str, tensor: torch.Tensor) -> int

Parameters:

• key (str): Object identifier

• tensor (torch.Tensor): The PyTorch tensor to insert or update

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This function requires torch to be installed and available in the environment.

upsert_tensor_from()

Upsert a tensor directly from a pre-allocated buffer. The buffer layout must be [TensorObjectHeader+layout metadata][tensor data], matching the layout used by get_tensor_into().

def upsert_tensor_from(self, key: str, buffer_ptr: int, size: int) -> int

Parameters:

• key (str): Object identifier

• buffer_ptr (int): Buffer pointer containing serialized tensor metadata and payload

• size (int): Actual serialized byte length of the tensor buffer

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This function is supported for dummy clients through the real client-owned shared-memory staging buffer.

batch_upsert_tensor_from()

Upsert multiple tensors directly from pre-allocated buffers. Each buffer must use layout [TensorObjectHeader+layout metadata][tensor data].

def batch_upsert_tensor_from(self, keys: List[str], buffer_ptrs: List[int], sizes: List[int]) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• buffer_ptrs (List[int]): List of serialized tensor buffer pointers

• sizes (List[int]): List of actual serialized byte lengths

Returns:

• List[int]: List of status codes for each tensor upsert

batch_upsert_tensor()

Upsert a batch of PyTorch tensors into the store (insert or update).

def batch_upsert_tensor(self, keys: List[str], tensors_list: List[torch.Tensor]) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• tensors_list (List[torch.Tensor]): List of tensors to insert or update

Returns:

• List[int]: List of status codes for each tensor operation.

Note: This function requires torch to be installed and available in the environment. It is supported for dummy clients through the real client-owned shared-memory staging buffer.

upsert_pub_tensor()

Upsert a PyTorch tensor with configurable replication settings (insert or update).

def upsert_pub_tensor(self, key: str, tensor: torch.Tensor, config: ReplicateConfig = None) -> int

Parameters:

• key (str): Unique object identifier

• tensor (torch.Tensor): PyTorch tensor to insert or update

• config (ReplicateConfig, optional): Replication configuration

Returns:

• int: Status code (0 = success, non-zero = error code)

Note: This function requires torch to be installed and available in the environment. It is supported for dummy clients through the real client-owned shared-memory staging buffer.

Example:

import torch
from mooncake.store import ReplicateConfig, SoftPinAction

tensor = torch.randn(100, 100)

config = ReplicateConfig()
config.replica_num = 2
config.soft_pin_action = SoftPinAction.ENABLE

result = store.upsert_pub_tensor("my_tensor", tensor, config)
if result == 0:
    print("Tensor upserted successfully")

batch_upsert_pub_tensor()

Batch upsert PyTorch tensors with configurable replication settings (insert or update).

def batch_upsert_pub_tensor(self, keys: List[str], tensors_list: List[torch.Tensor], config: ReplicateConfig = None) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• tensors_list (List[torch.Tensor]): List of tensors to insert or update

• config (ReplicateConfig, optional): Replication configuration

Returns:

• List[int]: List of status codes for each tensor operation.

Note: This function requires torch to be installed and available in the environment. It is supported for dummy clients through the real client-owned shared-memory staging buffer.

---

PyTorch Tensor Operations (Zero Copy)

These methods provide direct support for storing and retrieving PyTorch tensors. They automatically handle serialization and metadata, and include built-in support for Tensor Parallelism (TP) by automatically splitting and reconstructing tensor shards.

⚠️ Note: These methods require torch to be installed and available in the environment.

get_tensor_into()

Get a PyTorch tensor from the store directly into a pre-allocated buffer.

def get_tensor_into(self, key: str, buffer_ptr: int, size: int) -> torch.Tensor

Parameters:

• key (str): Base identifier of the tensor.

• buffer_ptr (int): The buffer pointer pre-allocated for tensor, and the buffer should be registered.

• size (int): The size of buffer.

Returns:

• torch.Tensor: The retrieved tensor (or shard). Returns None if not found.

batch_get_tensor()

Get a batch of PyTorch tensor from the store directly into a pre-allocated buffer.

def batch_get_tensor_into(self, base_keys: List[str], buffer_ptrs: List[int], sizes: List[int]) -> List[torch.Tensor]

Parameters:

• base_keys (List[str]): List of base identifiers.

• buffer_ptrs (List[int]): List of buffer pointers pre-allocated for tensor; buffers should be registered.

• sizes (List[int]): List of buffer sizes.

Returns:

• List[torch.Tensor]: List of retrieved tensors (or shards). Contains None for missing keys.

get_tensor_with_tp_into()

Get a PyTorch tensor from the store, specifically retrieving the shard corresponding to the given Tensor Parallel rank, directly into the pre-allocated buffer.

def get_tensor_with_tp_into(self, key: str, buffer_ptr: int, size: int, tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> torch.Tensor

Parameters:

• key (str): Base identifier of the tensor.

• buffer_ptr (int): The buffer pointer pre-allocated for tensor, and the buffer should be registered.

• size (int): The size of buffer.

• tp_rank (int): The tensor parallel rank to retrieve (default: 0). Fetches key key_tp_{rank} if tp_size > 1.

• tp_size (int): Total tensor parallel size (default: 1).

• split_dim (int): The dimension used during splitting (default: 0).

Returns:

• torch.Tensor: The retrieved tensor (or shard). Returns None if not found.

batch_get_tensor_with_tp_into()

Get a batch of PyTorch tensor shards from the store for a given Tensor Parallel rank, directly into the pre-allocated buffer.

def batch_get_tensor_with_tp_into(self, base_keys: List[str], buffer_ptrs: List[int], sizes: List[int], tp_rank: int = 0, tp_size: int = 1) -> List[torch.Tensor]

Parameters:

• base_keys (List[str]): List of base identifiers.

• buffer_ptrs (List[int]): List of buffer pointers pre-allocated for tensor; buffers should be registered.

• sizes (List[int]): List of buffer sizes.

• tp_rank (int): The tensor parallel rank to retrieve (default: 0).

• tp_size (int): Total tensor parallel size (default: 1).

Returns:

• List[torch.Tensor]: List of retrieved tensors (or shards). Contains None for missing keys.

put_tensor_from()

Put a PyTorch tensor into the store directly from a pre-allocated buffer (zero-copy). The buffer must contain data in the same layout as produced by get_tensor_into: [TensorMetadata][tensor data]. The buffer is only read during this call; no Python object references it.

def put_tensor_from(self, key: str, buffer_ptr: int, size: int) -> int

Parameters:

• key (str): Object identifier for the tensor.

• buffer_ptr (int): The buffer pointer; the buffer should be registered. Layout must be [TensorMetadata][tensor data].

• size (int): Actual serialized byte length of the data in the buffer (metadata + tensor bytes), not the buffer capacity.

Returns:

• int: Status code (0 = success, non-zero = error code).

batch_put_tensor_from()

Put a batch of PyTorch tensors into the store directly from pre-allocated buffers (zero-copy). Each buffer must contain data in the layout [TensorMetadata][tensor data], same as get_tensor_into.

def batch_put_tensor_from(self, keys: List[str], buffer_ptrs: List[int], sizes: List[int]) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers.

• buffer_ptrs (List[int]): List of buffer pointers; buffers should be registered.

• sizes (List[int]): List of actual serialized byte lengths for each buffer (metadata + tensor bytes), not buffer capacities.

Returns:

• List[int]: List of status codes for each tensor operation (0 = success, non-zero = error code).

put_tensor_with_tp_from()

Put a full tensor into the store directly from a pre-allocated buffer (zero-copy), for use with Tensor Parallelism. This is the zero-copy counterpart of put_tensor_with_tp(): the buffer must contain the complete tensor in layout [TensorMetadata][tensor data], and Mooncake will split it internally and store all shards under key_tp_<rank>.

def put_tensor_with_tp_from(self, key: str, buffer_ptr: int, size: int, tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> int

Parameters:

• key (str): Base identifier for the tensor.

• buffer_ptr (int): The buffer pointer; the buffer should be registered.

• size (int): Actual serialized byte length of the full tensor in the buffer.

• tp_rank (int): Kept for signature compatibility with put_tensor_with_tp() (default: 0). It does not mean “only write one shard”.

• tp_size (int): Total tensor parallel size (default: 1). If 1, equivalent to put_tensor_from(key, buffer_ptr, size).

• split_dim (int): Dimension along which the full tensor is split before storing shards.

Returns:

• int: Status code (0 = success, non-zero = error code).

batch_put_tensor_with_tp_from()

Put a batch of full tensors into the store directly from pre-allocated buffers (zero-copy). This is the zero-copy counterpart of batch_put_tensor_with_tp(): each buffer contains one full tensor in layout [TensorMetadata][tensor data], and Mooncake splits each tensor internally and stores all TP shards.

def batch_put_tensor_with_tp_from(self, base_keys: List[str], buffer_ptrs: List[int], sizes: List[int], tp_rank: int = 0, tp_size: int = 1, split_dim: int = 0) -> List[int]

Parameters:

• base_keys (List[str]): List of base identifiers.

• buffer_ptrs (List[int]): List of buffer pointers; buffers should be registered.

• sizes (List[int]): List of actual serialized byte lengths for each full-tensor buffer.

• tp_rank (int): Kept for signature compatibility with batch_put_tensor_with_tp() (default: 0). It does not select a single shard to write.

• tp_size (int): Total tensor parallel size (default: 1). If 1, equivalent to batch_put_tensor_from(base_keys, buffer_ptrs, sizes).

• split_dim (int): Dimension along which each full tensor is split before storing shards.

Returns:

• List[int]: List of status codes for each tensor operation (0 = success, non-zero = error code).

---

Batch Zero-Copy Operations

batch_put_from()

Store multiple objects from pre-registered buffers (zero-copy).

def batch_put_from(self, keys: List[str], buffer_ptrs: List[int], sizes: List[int], config: ReplicateConfig = None) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• buffer_ptrs (List[int]): List of memory addresses

• sizes (List[int]): List of buffer sizes

• config (ReplicateConfig, optional): Replication configuration

Returns:

• List[int]: List of status codes for each operation (0 = success, negative = error)

---

batch_get_into()

Retrieve multiple objects into pre-registered buffers (zero-copy).

def batch_get_into(self, keys: List[str], buffer_ptrs: List[int], sizes: List[int]) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• buffer_ptrs (List[int]): List of memory addresses

• sizes (List[int]): List of buffer sizes

Returns:

• List[int]: List of bytes read for each operation (positive = success, negative = error)

⚠️ Store-managed Buffer Required: All buffers must resolve to Store-managed registered memory before batch zero-copy operations.

Example:

Click to expand: Batch zero-copy retrieval example

# Prepare buffers
keys = ["tensor1", "tensor2", "tensor3"]
buffer_size = 1024 * 1024  # 1MB each
buffers = []
buffer_ptrs = []

for i in range(len(keys)):
    buffer = np.empty(buffer_size, dtype=np.uint8)
    buffers.append(buffer)
    buffer_ptrs.append(buffer.ctypes.data)
    store.register_buffer(buffer.ctypes.data, buffer_size)

# Batch retrieve
sizes = [buffer_size] * len(keys)
results = store.batch_get_into(keys, buffer_ptrs, sizes)

# Check results
for key, result in zip(keys, results):
    if result > 0:
        print(f"Retrieved {key}: {result} bytes")
    else:
        print(f"Failed to retrieve {key}: error {result}")

# Cleanup
for ptr in buffer_ptrs:
    store.unregister_buffer(ptr)

---

batch_put_from_multi_buffers()

Store multiple objects from multiple pre-registered buffers (zero-copy).

def batch_put_from_multi_buffers(self, keys: List[str], all_buffer_ptrs: List[List[int]], all_sizes: List[List[int]],
                                 config: ReplicateConfig = None) -> List[int]

Parameters:

• keys (List[str]): List of object identifiers

• all_buffer_ptrs (List[int]): all List of memory addresses

• sizes (List[int]): all List of buffer sizes

• config (ReplicateConfig, optional): Replication configuration

Returns:

• List[int]: List of status codes for each operation (0 = success, negative = error)

---

batch_get_into_multi_buffers()

Retrieve multiple objects into multiple pre-registered buffers (zero-copy).

def batch_get_into_multi_buffers(self, keys: List[str], all_buffer_ptrs: List[List[int], all_sizes: List[List[int]) ->
List[int]

Parameters:

• keys (List[str]): List of object identifiers

• all_buffer_ptrs (List[int]): List of memory addresses

• all_sizes (List[int]): List of buffer sizes

Returns:

• List[int]: List of bytes read for each operation (positive = success, negative = error)

⚠️ Store-managed Buffer Required: All buffers must resolve to Store-managed registered memory before batch zero-copy operations.

Example:

Click to expand: Batch zero-copy put and get for multiple buffers example

tensor = torch.ones(10, 61, 128*1024, dtype=torch.int8)
data_ptr = tensor.data_ptr()
store.register_buffer(data_ptr, 10*61*128*1024)

target_tensor = torch.zeros(10, 61, 128*1024, dtype=torch.int8)
target_data_ptr = target_tensor.data_ptr()
store.register_buffer(target_data_ptr, 10*61*128*1024)

all_local_addrs = []
all_remote_addrs = []
all_sizes = []
keys = []
for block_i in range(10):
  local_addrs = []
  remote_addrs = []
  sizes = []
  for _ in range(61):
    local_addrs.append(data_ptr)
    remote_addrs.append(target_data_ptr)
    sizes.append(128*1024)
    data_ptr += 128*1024
    target_data_ptr += 128*1024
  all_local_addrs.append(local_addrs)
  all_remote_addrs.append(remote_addrs)
  all_sizes.append(sizes)
  keys.append(f"kv_{rank}_{block_i}")

config = ReplicateConfig()
config.prefer_alloc_in_same_node = True
store.batch_put_from_multi_buffers(keys, all_local_addrs, all_sizes, config)
store.batch_get_into_multi_buffers(keys, all_remote_addrs, all_sizes, True)

store.unregister_buffer(tensor.data_ptr())
store.unregister_buffer(target_tensor.data_ptr())

---

Session-based ranged multi-buffer transfer

For layerwise KV load/save, resolve Master metadata once per object, then transfer object-byte ranges across multiple buffers without re-querying Master on every layer.

Typical flow:

• Get: batch_get_session_start → batch_get_into_multi_buffer_ranges (per layer) → batch_get_session_end

• Put: batch_put_session_start → batch_put_from_multi_buffer_ranges (per layer) → batch_put_session_end / batch_put_session_revoke

Get sessions cache a filtered QueryResult (single complete memory replica + lease). Range calls only check the cached lease locally (zero Master RPCs). Put sessions reserve object space via Master BatchPutStart and finalize with BatchPutEnd.

Put sessions write MEMORY replicas only. nof_replica_num > 0 is accepted only for flexible dual-replica configs (replica_num == 1 and nof_replica_num == 1), where batch_put_session_end finalizes MEMORY and revokes the unused NoF reservation. Reliable multi-replica NoF configs are rejected at session start. end / revoke seal the session (no further range writes) and wait for in-flight range transfers before talking to Master.

⚠️ Store-managed Buffer Required: All buffers must resolve to Store-managed registered memory before ranged zero-copy operations.

batch_get_session_start()

Query replicas once and open a get session for the given keys.

def batch_get_session_start(self, keys: List[str]) -> List[int]

Parameters:

• keys (List[str]): Object identifiers

Returns:

• List[int]: Per-key status (0 = success, negative = error)

batch_get_into_multi_buffer_ranges()

Ranged get into multiple buffers using an active get session (no Master RPC).

def batch_get_into_multi_buffer_ranges(
    self,
    keys: List[str],
    all_buffer_ptrs: List[List[int]],
    all_sizes: List[List[int]],
    all_src_offsets: List[List[int]],
) -> List[int]

Parameters:

• keys (List[str]): Object identifiers (must have an active get session)

• all_buffer_ptrs (List[List[int]]): Per-key list of destination buffer addresses

• all_sizes (List[List[int]]): Per-key list of transfer sizes in bytes

• all_src_offsets (List[List[int]]): Per-key list of object-byte source offsets

Returns:

• List[int]: Bytes transferred per key (positive = success, negative = error)

batch_get_session_end()

Drop cached get-session metadata for the given keys.

def batch_get_session_end(self, keys: List[str]) -> int

Parameters:

• keys (List[str]): Object identifiers

Returns:

• int: 0 on success, negative on error

batch_put_session_start()

Reserve objects and open a put session without transferring data.

def batch_put_session_start(
    self,
    keys: List[str],
    sizes: List[int],
    config: ReplicateConfig = None,
) -> List[int]

Parameters:

• keys (List[str]): Object identifiers

• sizes (List[int]): Full object sizes in bytes

• config (ReplicateConfig, optional): Replication configuration (applies at start only). If group_ids is set, its length must equal len(keys). When some keys already have a put session, they are skipped and group_ids is filtered to match the remaining keys.

Returns:

• List[int]: Per-key status (0 = success, negative = error)

batch_put_from_multi_buffer_ranges()

Ranged put from multiple buffers using an active put session (no Master RPC).

def batch_put_from_multi_buffer_ranges(
    self,
    keys: List[str],
    all_buffer_ptrs: List[List[int]],
    all_sizes: List[List[int]],
    all_dst_offsets: List[List[int]],
) -> List[int]

Parameters:

• keys (List[str]): Object identifiers (must have an active put session)

• all_buffer_ptrs (List[List[int]]): Per-key list of source buffer addresses

• all_sizes (List[List[int]]): Per-key list of transfer sizes in bytes

• all_dst_offsets (List[List[int]]): Per-key list of object-byte destination offsets

Returns:

• List[int]: Bytes transferred per key (positive = success, negative = error)

batch_put_session_end()

Finalize a put session and make objects readable.

def batch_put_session_end(self, keys: List[str]) -> List[int]

Parameters:

• keys (List[str]): Object identifiers

Returns:

• List[int]: Per-key status (0 = success, negative = error)

batch_put_session_revoke()

Abort an incomplete put session and release reserved space.

def batch_put_session_revoke(self, keys: List[str]) -> List[int]

Parameters:

• keys (List[str]): Object identifiers

Returns:

• List[int]: Per-key status (0 = success, negative = error)

Example:

Click to expand: Session ranged put/get example

import numpy as np

page = 1024
layers = 4
keys = ["block0", "block1"]
object_sizes = [page * layers] * len(keys)

# Prepare one registered buffer per layer for each key
src = [np.full(page, i, dtype=np.uint8) for i in range(layers)]
dst = [np.zeros(page, dtype=np.uint8) for _ in range(layers)]
for buf in src + dst:
    store.register_buffer(buf.ctypes.data, buf.nbytes)

assert all(rc == 0 for rc in store.batch_put_session_start(keys, object_sizes))
for layer in range(layers):
    ptrs = [[src[layer].ctypes.data] for _ in keys]
    sizes = [[page] for _ in keys]
    offsets = [[layer * page] for _ in keys]
    rcs = store.batch_put_from_multi_buffer_ranges(keys, ptrs, sizes, offsets)
    assert all(rc == page for rc in rcs)
assert all(rc == 0 for rc in store.batch_put_session_end(keys))

assert all(rc == 0 for rc in store.batch_get_session_start(keys))
for layer in range(layers):
    ptrs = [[dst[layer].ctypes.data] for _ in keys]
    sizes = [[page] for _ in keys]
    offsets = [[layer * page] for _ in keys]
    rcs = store.batch_get_into_multi_buffer_ranges(keys, ptrs, sizes, offsets)
    assert all(rc == page for rc in rcs)
assert store.batch_get_session_end(keys) == 0

MooncakeHostMemAllocator Class

The MooncakeHostMemAllocator class provides host memory allocation capabilities for Mooncake Store operations.

Class Definition

from mooncake.store import MooncakeHostMemAllocator

# Create an allocator instance
allocator = MooncakeHostMemAllocator()

Methods

alloc()

Allocate memory from the host memory pool.

def alloc(self, size: int) -> int

Parameters:

• size (int): Size of memory to allocate in bytes

Returns:

• int: Memory address as integer, or 0 on failure

Example:

allocator = MooncakeHostMemAllocator()
ptr = allocator.alloc(1024 * 1024)  # Allocate 1MB
if ptr != 0:
    print(f"Allocated memory at address: {ptr}")

free()

Free previously allocated memory.

def free(self, ptr: int) -> int

Parameters:

• ptr (int): Memory address to free

Returns:

• int: Status code (0 = success, non-zero = error code)

Example:

result = allocator.free(ptr)
if result == 0:
    print("Memory freed successfully")

---

bind_to_numa_node Function

The bind_to_numa_node function binds the current thread and memory allocation preference to a specified NUMA node.

Function Definition

from mooncake.store import bind_to_numa_node

# Bind to NUMA node
bind_to_numa_node(node: int)

Parameters:

• node (int): NUMA node number to bind to

Example:

from mooncake.store import bind_to_numa_node

# Bind current thread to NUMA node 0
bind_to_numa_node(0)

---

Error Handling

Most methods return integer status codes:

• 0: Success

• Negative values: Error codes (for methods that can return data size)

For methods that return data (get, get_batch, get_buffer, get_tensor):

• Return the requested data on success

• Return empty/None on failure or key not found

📋 Complete Error Codes Reference: See Error Code Explanation for detailed descriptions of all error codes and their meanings.

---

Performance Tips

1. Use batch operations when working with multiple objects to reduce network overhead

2. Use zero-copy APIs (put_from, get_into) for large data transfers

3. Register buffers once and reuse them for multiple operations

4. Configure replication appropriately - more replicas provide better availability but use more storage

5. Use soft pinning for frequently accessed objects to keep them in memory

6. Choose RDMA protocol when available for maximum performance