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Key-value stores

Overview​

LangChain provides a key-value store interface for storing and retrieving data.

LangChain includes a BaseStore interface, which allows for storage of arbitrary data. However, LangChain components that require KV-storage accept a more specific BaseStore<string, Uint8Array> instance that stores binary data (referred to as a ByteStore), and internally take care of encoding and decoding data for their specific needs.

This means that as a user, you only need to think about one type of store rather than different ones for different types of data.

Usage​

The key-value store interface in LangChain is used primarily for:

  1. Caching embeddings via CachedBackedEmbeddings to avoid recomputing embeddings for repeated queries or when re-indexing content.

  2. As a simple Document persistence layer in some retrievers.

Please see these how-to guides for more information:

Interface​

All BaseStores support the following interface. Note that the interface allows for modifying multiple key-value pairs at once:

  • mget(keys: string[]): Promise<(Uint8Array | undefined)[]>: get the contents of multiple keys, returning undefined if the key does not exist
  • mset(keyValuePairs: [string, Uint8Array][]): Promise<void>: set the contents of multiple keys
  • mdelete(keys: string[]): Promise<void>: delete multiple keys
  • yieldKeys(prefix?: string): AsyncIterator<string>: yield all keys in the store, optionally filtering by a prefix

Integrations​

Please reference the stores integration page for a list of available key-value store integrations.

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