opensolr-haystack

Haystack integration for Opensolr — managed Apache Solr as a DocumentStore, with server-side embeddings and native hybrid (BM25 + kNN) retrieval.

No embedder components needed in your pipeline — texts and queries are embedded on Opensolr's GPU infrastructure (multilingual E5-large-instruct, 1024 dimensions, cosine).

Product page: opensolr.com/langchain · free 15-day trial, no card, at opensolr.com

pip install opensolr-haystack

Quickstart

from haystack import Document, Pipeline
from haystack_integrations.document_stores.opensolr import OpensolrDocumentStore
from haystack_integrations.components.retrievers.opensolr import OpensolrHybridRetriever

# credentials default to OPENSOLR_EMAIL / OPENSOLR_API_KEY env vars
store = OpensolrDocumentStore(index="mysite__dense", create_if_missing=True)

store.write_documents([
    Document(content="Hybrid search fuses BM25 with vector similarity"),
    Document(content="Cats sleep sixteen hours a day"),
])

pipe = Pipeline()
pipe.add_component("retriever", OpensolrHybridRetriever(document_store=store))
result = pipe.run({"retriever": {"query": "how do keyword and semantic search combine?"}})
print(result["retriever"]["documents"])

Note there is no embedder in the pipeline — not for documents, not for the query. The store embeds server-side at both index and query time.

Hybrid retrieval

OpensolrHybridRetriever fuses BM25 and kNN scores per document via Opensolr's native {!hybrid} Solr query parser:

OpensolrHybridRetriever(
    document_store=store,
    top_k=10,
    hybrid=True,     # False = pure semantic kNN
    alpha=0.5,       # 0 = all semantic … 1 = all lexical
)

Standard Haystack filters are supported and map to Solr fq:

pipe.run({"retriever": {
    "query": "search engines",
    "filters": {"field": "meta.category", "operator": "==", "value": "docs"},
}})

Notes

• Vector-enabled indexes run on Opensolr's Solr 9.x environments — currently us (Chicago), de (Germany), fi (Finland). Additional dedicated regions can be deployed on request (paid add-on): support@opensolr.com.
• Every index is also plain Apache Solr with the native /select API — facets, highlighting, spellcheck included.
• Siblings: langchain-opensolr · llama-index-opensolr · opensolr-mcp

MIT license.