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[str, bytes] 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:

• How to cache embeddings guide.
• How to retriever using multiple vectors per document.

Interface

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

• mget(key: Sequence[str]) -> List[Optional[bytes]]: get the contents of multiple keys, returning None if the key does not exist
• mset(key_value_pairs: Sequence[Tuple[str, bytes]]) -> None: set the contents of multiple keys
• mdelete(key: Sequence[str]) -> None: delete multiple keys
• yield_keys(prefix: Optional[str] = None) -> Iterator[str]: 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.