Framework integrations

polign_db works as a vector store in LangChain and LlamaIndex. Each integration is a small Python package built on the polign client, so it talks to the same server and needs nothing extra on the server side.

Both need a running server. For a first try, start one on your machine:

polign-server -store fs:/var/lib/polign

It listens on http://localhost:23000. Get started covers installing the binary and pointing it at a bucket.

LangChain

pip install langchain-polign

from langchain_openai import OpenAIEmbeddings
from langchain_polign import PolignVectorStore

store = PolignVectorStore(
    embedding=OpenAIEmbeddings(),
    collection="docs",
    url="http://localhost:23000",
)

store.add_texts(
    ["cats purr", "dogs bark"],
    metadatas=[{"lang": "en", "score": 0.9}, {"lang": "en", "score": 0.4}],
)

store.similarity_search("purring", k=1, filter={"score": {"$gte": 0.5}})
store.similarity_search_with_relevance_scores("barking", k=2)
store.max_marginal_relevance_search("animals", k=2, fetch_k=10)

store.delete(filter={"lang": "fr"})      # or store.delete(ids=[...])

retriever = store.as_retriever(search_kwargs={"k": 4, "filter": {"lang": "en"}})

filter is the same metadata language as the Python client: a plain mapping is equality, and $eq, $ne, $in, $gt, $gte, $lt, $lte, $exists, $and, $or, and $not build richer predicates.

similarity_search_with_score returns the distance, where smaller is closer. similarity_search_with_relevance_scores turns it into a score between 0 and 1. The package passes LangChain's standard vector store test suite. Source and the full API are in the langchain-polign README.

LlamaIndex

pip install llama-index-vector-stores-polign

from llama_index.core import StorageContext, VectorStoreIndex
from llama_index.vector_stores.polign import PolignVectorStore

store = PolignVectorStore(collection_name="docs", url="http://localhost:23000")
index = VectorStoreIndex.from_documents(
    documents, storage_context=StorageContext.from_defaults(vector_store=store)
)

index.as_retriever(similarity_top_k=5).retrieve("what purrs?")
index.delete_ref_doc("document-id")     # removes every chunk of that document

# reopen later without re-indexing
index = VectorStoreIndex.from_vector_store(store)

LlamaIndex MetadataFilters are translated for you. Supported operators are EQ, NE, GT, GTE, LT, LTE, IN, NIN, ANY, ALL, CONTAINS, and IS_EMPTY, combined with AND, OR, and NOT. TEXT_MATCH is not supported.

Source and the full API are in the llama-index-vector-stores-polign README.

Keyword and hybrid search

Both packages store the document text in the metadata key text. That is the field the server's keyword index reads, so keyword and hybrid search work without setup. In LangChain, call them directly:

store.lexical_search("brown fox", k=5)            # keyword only
store.hybrid_search("brown fox", k=5, alpha=0.6)  # vector and keyword, weighted
store.hybrid_search("brown fox", k=5)             # vector and keyword, rank fusion

In LlamaIndex, pick the TEXT_SEARCH or HYBRID query mode.

Keyword search needs a server started with -store. A new document becomes searchable by keyword once the server has written it to the bucket, about half a minute with default settings. Vector search sees it right away.

What gets stored

• The document or node id becomes the record id, so adding the same id again replaces it.
• Metadata that is a string, number, boolean, or a flat list of those is stored as is and can be filtered on.
• Nested objects and empty values are saved as text and restored when you read them back. They cannot be filtered on.
• A collection is created by the first write and takes its size from the first vector.

Limits

• Removing a whole collection needs the server's collection API (-byo-store). Without it, delete by filter, or call clear() in LlamaIndex, which removes every record.
• MMR fetches the candidate vectors in one extra request, because search results do not include vectors.
• The LlamaIndex async methods run the client on a worker thread.

Source & license

Both packages are open source under the Apache License 2.0 and live next to the client in github.com/Polign/polign. Bug reports and pull requests go there.