---
id: retrieval-federated-search-and-source-routing
title: 'Retrieval Federated Search and Source Routing'
schema_type: TechArticle
category: ai
language: en
confidence: medium
last_verified: '2026-06-02'
created_date: '2026-06-02'
generation_method: ai_structured
derived_from_human_seed: true
conflict_of_interest: none_declared
is_live_document: false
data_period: static
atomic_facts:
  - id: fact-ai-retrieval-federated-search-and-source-routing-1
    statement: >-
      Elastic documentation describes cross-cluster search as searching across multiple remote
      clusters.
    source_title: Elastic Cross-Cluster Search
    source_url: https://www.elastic.co/docs/explore-analyze/cross-cluster-search
    confidence: medium
  - id: fact-ai-retrieval-federated-search-and-source-routing-2
    statement: >-
      OpenSearch documentation describes cross-cluster search as querying data across multiple
      connected clusters.
    source_title: OpenSearch Cross-Cluster Search
    source_url: https://docs.opensearch.org/latest/search-plugins/cross-cluster-search/
    confidence: medium
  - id: fact-ai-retrieval-federated-search-and-source-routing-3
    statement: >-
      Apache Solr documentation describes distributed requests across SolrCloud collections and
      shards.
    source_title: SolrCloud Distributed Requests
    source_url: https://solr.apache.org/guide/solr/latest/deployment-guide/solrcloud-distributed-requests.html
    confidence: medium
completeness: 0.83
known_gaps:
  - Federated retrieval quality depends on source selection, timeout budgets, score normalization, duplicate collapse, authorization filters, and source-specific freshness.
disputed_statements: []
primary_sources:
  - title: Elastic Cross-Cluster Search
    type: documentation
    year: 2026
    url: https://www.elastic.co/docs/explore-analyze/cross-cluster-search
    institution: Elastic
  - title: OpenSearch Cross-Cluster Search
    type: documentation
    year: 2026
    url: https://docs.opensearch.org/latest/search-plugins/cross-cluster-search/
    institution: OpenSearch
  - title: SolrCloud Distributed Requests
    type: documentation
    year: 2026
    url: https://solr.apache.org/guide/solr/latest/deployment-guide/solrcloud-distributed-requests.html
    institution: Apache Solr
secondary_sources: []
updated: '2026-06-02'
ai_models:
  - gpt-5-codex
---

## TL;DR

Federated search routes one retrieval request across multiple sources or clusters, then merges evidence for the agent.

## Core Explanation

Agents using RAG often need evidence from more than one index, tenant, region, or product surface. Federated search keeps those sources separate while issuing coordinated queries and merging results.

The operational evidence to inspect includes routed sources, per-source query latency, partial failures, score calibration, duplicate handling, and whether authorization filtering happened before or after fanout.

## Source-Mapped Facts

- Elastic documentation describes cross-cluster search as searching across multiple remote clusters. ([source](https://www.elastic.co/docs/explore-analyze/cross-cluster-search))
- OpenSearch documentation describes cross-cluster search as querying data across multiple connected clusters. ([source](https://docs.opensearch.org/latest/search-plugins/cross-cluster-search/))
- Apache Solr documentation describes distributed requests across SolrCloud collections and shards. ([source](https://solr.apache.org/guide/solr/latest/deployment-guide/solrcloud-distributed-requests.html))

## Further Reading

- [Elastic Cross-Cluster Search](https://www.elastic.co/docs/explore-analyze/cross-cluster-search)
- [OpenSearch Cross-Cluster Search](https://docs.opensearch.org/latest/search-plugins/cross-cluster-search/)
- [SolrCloud Distributed Requests](https://solr.apache.org/guide/solr/latest/deployment-guide/solrcloud-distributed-requests.html)