| name | nlweb-retrieval-backends |
| description | Choose and configure NLWeb retrieval backends — Qdrant (local + remote), Azure AI Search, Elasticsearch, OpenSearch (with/without k-NN), Postgres pgvector, Milvus, Snowflake Cortex Search, Cloudflare AutoRAG, Shopify MCP, and Bing Web Search. Covers `config_retrieval.yaml`, the single `write_endpoint` rule, parallel read-fanout with URL dedup, and per-backend setup pages. Use when picking a retrieval store, migrating between backends, or debugging "results are empty."
|
NLWeb Retrieval Backends
Before writing code
Fetch live docs:
- Fetch https://github.com/nlweb-ai/NLWeb/blob/main/docs/nlweb-retrieval.md for the architectural overview.
- Fetch https://github.com/nlweb-ai/NLWeb/blob/main/config/config_retrieval.yaml for the canonical list of endpoint names and their defaults — config keys move release to release.
- Pick the per-backend setup page from
docs/setup-*.md (Qdrant, Azure AI Search, Elasticsearch, OpenSearch, Postgres, Snowflake, Cloudflare AutoRAG).
- Inspect
AskAgent/python/retrieval_providers/<backend>.py for the exact client signature and required env vars.
- Verify the embedding dimension and metric (cosine/dot/L2) the backend expects — must match the embedding provider.
Conceptual Architecture
The Read-Fanout, Single-Write Pattern
NLWeb does something unusual: it reads from every enabled retrieval endpoint in parallel and deduplicates by URL, but writes go to exactly one write_endpoint. This means:
- You can run a hybrid index (e.g., local Qdrant for site content + Bing for fresh news) without code changes
- You migrate between backends by re-running
db_load against the new write_endpoint
- "Result quality" is the union of all enabled stores — a noisy backend pollutes the top-k
All Supported Backends
| Endpoint key (config_retrieval.yaml) | Backend | Notes |
|---|
qdrant_local | Qdrant file-backed | Default-enabled; data in ../data/db |
qdrant_url | Qdrant remote | Set URL + API key in env |
nlweb_west | Azure AI Search | Default-enabled MS-hosted demo instance — usually disable |
azure_ai_search | Azure AI Search (your own) | Bring your own index name |
milvus | Milvus | Flagged "under development" in YAML |
elasticsearch | Elasticsearch | dense_vector + int8_hnsw |
opensearch_knn | OpenSearch + k-NN plugin | The recommended OpenSearch path |
opensearch_script | OpenSearch no plugin | script_score fallback, slower |
postgres | Postgres + pgvector | Good if you already run Postgres |
snowflake_cortex_search_1 | Snowflake Cortex Search | Data lives in Snowflake tables |
cloudflare_autorag | Cloudflare AutoRAG | Indexing managed by CF; ingest via R2 |
shopify_mcp | Shopify's MCP endpoint | Default-enabled; live proxy, no ingest |
bing_search | Bing Web Search API | Live web fallback; not a vector store |
Read vs Write
Every endpoint declares:
enabled: true/false — whether /ask queries itread: true/false — finer-grained: enable for reads- (only one endpoint should be the
write_endpoint)
The default config has qdrant_local, nlweb_west, and shopify_mcp enabled — for local dev disable the last two.
Choosing a Backend
| If you need... | Use |
|---|
| Local dev with no cloud deps | qdrant_local |
| Largest scale + Microsoft-stack | azure_ai_search |
| Already on AWS | opensearch_knn |
| Already on Postgres | postgres (pgvector) |
| Live e-commerce catalog | shopify_mcp |
| Snowflake-resident data | snowflake_cortex_search_1 |
| Edge deployment | cloudflare_autorag |
| Live news/freshness | bing_search (combine with a vector backend) |
Embedding Dimension Compatibility
Each backend stores fixed-dimension vectors. The embedding provider must emit the same dimension:
| Embedding provider | Default model | Dim |
|---|
OpenAI text-embedding-3-small | default | 1536 |
OpenAI text-embedding-3-large | — | 3072 |
Azure OpenAI text-embedding-3-small | default | 1536 |
Gemini text-embedding-004 | — | 768 |
Snowflake arctic-embed-m-v1.5 | — | 768 |
Elasticsearch multilingual-e5-small | — | 384 |
Pick the embedding provider FIRST, configure the backend's index to match THAT dimension, then ingest.
Metric Compatibility
Most NLWeb providers use cosine similarity. When creating a new index manually (Azure AI Search, OpenSearch, Postgres) make sure the metric matches what the retrieval provider class expects. Look in retrieval_providers/<backend>.py for the metric the SDK call passes.
The nlweb_west Trap
nlweb_west is a Microsoft-hosted demo Azure AI Search instance that's enabled by default. For most users this:
- Pollutes results with MS demo data
- Requires the demo's Azure credentials to even connect
- Costs nothing but adds latency
Disable it in local dev unless you specifically want the demo content.
Implementation Guidance
Switching the Write Endpoint
Edit config/config_retrieval.yaml:
write_endpoint: azure_ai_search
endpoints:
qdrant_local:
enabled: false
azure_ai_search:
enabled: true
api_key_env: AZURE_SEARCH_API_KEY
endpoint_env: AZURE_SEARCH_ENDPOINT
index_name: nlweb-main
Then re-ingest:
python -m data_loading.db_load --only-delete delete-site <site>
python -m data_loading.db_load <source> <site> --database azure_ai_search
Running Multiple Backends in Parallel
Leave several enabled: true simultaneously — /ask will fan out reads, dedup by URL. Useful for:
- Hybrid: Postgres (cheap) for site content + Bing for live web facts
- A/B: Qdrant + Azure AI Search to compare retrieval quality
Adding a New Backend Provider
If NLWeb doesn't ship the backend you need:
- Subclass the base in
retrieval_providers/ — look at any existing one for the contract (search, upsert, delete-by-site).
- Add an endpoint entry in
config_retrieval.yaml.
- Register the class in the provider factory (verify location in current code).
- Ingest a test site.
Backend-Specific Notes
Qdrant local: zero setup; collection lives at ../data/db. To reset, delete the directory.
Azure AI Search: create the index manually (or via the setup doc's ARM template). Vector field must be vector (or whatever the provider class names it — verify).
Postgres + pgvector: CREATE EXTENSION vector; then ensure the column is vector(1536) or whichever dim matches your embedding. NLWeb uses cosine distance by default.
Snowflake Cortex Search: data is in a Snowflake table; you create a CORTEX SEARCH SERVICE over it. NLWeb queries via the Cortex API. No db_load.py involvement.
Cloudflare AutoRAG: upload files to R2, point AutoRAG at the bucket, wire NLWeb to the AutoRAG endpoint. CF manages indexing.
Shopify MCP: zero ingest. NLWeb proxies queries to a Shopify store's MCP endpoint. Configure the shop domain per-site. Disable for non-commerce deployments.
Bing: API key required; only useful combined with at least one vector backend (Bing returns web pages, not your indexed content).
Debugging Empty Results
Diagnostic ladder:
curl http://localhost:8000/sites — site is registered?curl 'http://localhost:8000/ask?query=test&site=X&mode=list&streaming=false' — any results at all?- Disable all backends except the one you wrote to — does the write_endpoint return results?
- Check embedding dimension:
python -c "from embedding_providers import get_default; print(get_default().dim)" (verify exact API) and compare to your index schema.
- Inspect the raw store:
qdrant CLI / Azure Search Studio / SELECT count(*) FROM index for Postgres.
- Re-ingest with the embedding provider that matches the index.
Always re-fetch config_retrieval.yaml from the live repo before generating config — keys change.
