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Multi_Server_Client_Hashing.md

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graph LR
    HashClient["HashClient"]
    RendezvousHash["RendezvousHash"]
    Client["Client"]
    murmur3["murmur3"]
    PooledClient["PooledClient"]
    Serialization_Deserialization_Module["Serialization/Deserialization Module"]
    MemcacheError["MemcacheError"]
    HashClient -- "Manages/Uses" --> Client
    HashClient -- "Composes/Uses" --> RendezvousHash
    RendezvousHash -- "Depends on" --> murmur3
    Client -- "Uses" --> Serialization_Deserialization_Module
    Client -- "Raises/Handles" --> MemcacheError
    PooledClient -- "Inherits from" --> Client
    Serialization_Deserialization_Module -- "Used by" --> Client
    MemcacheError -- "Inherited by" --> specific_error_types
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The Multi-Server Client & Hashing subsystem in pymemcache is fundamental for enabling distributed caching across multiple Memcached servers. It achieves this by extending the basic single-server client functionality with intelligent key routing using consistent hashing.

HashClient

The primary client interface for interacting with multiple Memcached servers. It abstracts away the complexity of routing keys to the correct server by employing a consistent hashing algorithm, enabling distributed caching and fault tolerance. It manages a collection of individual Client instances, one for each server.

Related Classes/Methods:

RendezvousHash

Implements the Rendezvous Hashing (HRW) algorithm, a consistent hashing technique crucial for HashClient. It deterministically distributes keys among a dynamic set of servers, ensuring that when servers are added or removed, only a minimal number of keys need to be remapped, thus reducing cache misses.

Related Classes/Methods:

Client [Expand]

The foundational client class responsible for direct, low-level communication with a single Memcached server. It handles the Memcached protocol interactions, serialization/deserialization of data, and basic error handling. HashClient builds upon this class by managing multiple instances of it.

Related Classes/Methods:

murmur3

This module provides the Murmur3 hash function, a fast, non-cryptographic hash function. It is specifically used by the RendezvousHash algorithm to compute hash values for server keys and data keys, which is essential for the deterministic distribution of keys.

Related Classes/Methods:

PooledClient

A specialized client that extends the Client class to manage a pool of connections to a single Memcached server. This improves performance by reusing established connections rather than opening new ones for each operation.

Related Classes/Methods:

  • pymemcache.client.pooled

Serialization/Deserialization Module

This module provides the mechanisms for converting Python objects into a format suitable for storage in Memcached (serialization) and converting them back into Python objects upon retrieval (deserialization). It supports various serialization methods.

Related Classes/Methods:

MemcacheError

The base class for all exceptions raised by the pymemcache client library, indicating various issues that can occur during Memcached operations (e.g., network errors, server errors, input errors).

Related Classes/Methods:

FAQ