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Apache Solr

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by Apache Software Foundation · since 2006 · also known as Solr, SolrCloud

The original Lucene search server: battle-tested, Apache-governed, now with GPU-accelerated vectors.

search enginedocumentvectorspatialdatabase engineopen source (permissive)mature
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Overview

Solr is the Apache Software Foundation's search server built on Lucene, and it predates Elasticsearch by years. It is configuration-heavy but extremely capable: faceting, grouping, joins, streaming expressions, learning-to-rank and, since 9.x, dense vector search. Solr 10.0 (March 2026) moved to Java 21 and Lucene 10, added quantized vectors and cuVS GPU indexing, and trimmed legacy modules. It fits teams that want fully Apache-licensed, community-run enterprise search and are comfortable running ZooKeeper-backed SolrCloud clusters.

Full-text searchVector searchRAG & AI memoryGeospatialContent & catalogs

Strengths & trade-offs

Strengths

  • +Mature faceting, grouping, highlighting and spell-checking
  • +Apache governance with no commercial license strings
  • +Streaming expressions and parallel SQL for analytics over indexes
  • +Dense vector search with quantization and GPU (cuVS) index builds in 10.x
  • +Official Kubernetes operator

Trade-offs

  • −XML-era configuration and schema management feel dated
  • −Running ZooKeeper adds operational overhead
  • −Smaller and slower-moving ecosystem than Elasticsearch/OpenSearch
  • −Fewer managed-service choices

Great for

  • +Enterprise and intranet search
  • +Digital library and publishing search
  • +E-commerce catalog faceting
  • +Hybrid keyword and vector retrieval on existing Solr estates

Think twice for

  • −Log analytics at scale
  • −Teams wanting a zero-config search API
  • −Serverless or embedded deployments

Capabilities

Native or official first-party support · 11 of 25 tracked

✓Joins
✓Secondary indexes
✓Full-text search
✓Vector search
✓Geospatial
✓JSON
✓TTL / expiry
✓Durable persistence
✓Compression
✓Role-based access
✓Online schema changes
–Transactions
–Change data capture
–Triggers
–Stored procedures
–Materialized views
–Pub/Sub
–Columnar storage
–In-memory
–Encryption at rest
–Time travel
–Branching
–Streaming ingest
–Offline sync
–Runs in WebAssembly

Scale & consistency

Comfortable data size
Large · ≤ 1 PB
Horizontal scaling
Native
Multi-region
Read replicas
Transactions
Limited ACID
Consistency
Eventual
Schema
Flexible
Architecture
Distributed, Client server
Query languages
Lucene query syntax, JSON Request API, Streaming Expressions, SQL

SolrCloud shards and replicates collections with ZooKeeper coordination; cross-DC setups use replica types or the cross-DC manager.

Deployment

Self-hosted Vendor-managed cloud Serverless Embedded Edge Kubernetes operator
SearchStax Managed SearchSearchStax

Ecosystem

apis & protocolsREST/JSON, SolrJ
client languagesJava, Python, JavaScript, PHP, Ruby, .NET

Alternatives to Apache Solr

Compare all→
ElasticsearchSearch Engine75.1

Lucene-based distributed search and analytics engine for text, vectors, logs and metrics.

apache-solr vs elasticsearch →
OpenSearchSearch Engine56.6

Apache-licensed, foundation-governed fork of Elasticsearch for search, vectors and observability.

apache-solr vs opensearch →
VespaSearch Engine23.8

Big-data serving engine for search, recommendation and RAG with tensors and ML ranking.

apache-solr vs vespa →
Manticore SearchSearch Engine19.2

Fast SQL-first search database, forked from Sphinx, with columnar storage and vector KNN.

apache-solr vs manticore-search →
Apache LuceneSearch Engine38.6

The Java search library at the heart of Elasticsearch, OpenSearch and Solr, now with HNSW vectors.

apache-solr vs apache-lucene →
Azure AI SearchSearch Engine32.4

Microsoft's managed search service for full-text, vector, hybrid and agentic retrieval on Azure.

apache-solr vs azure-ai-search →

Apache Solr FAQ

What is Apache Solr?

Apache Solr is a search engine database by Apache Software Foundation, first released in 2006. Solr is the Apache Software Foundation's search server built on Lucene, and it predates Elasticsearch by years. It is configuration-heavy but extremely capable: faceting, grouping, joins, streaming expressions, learning-to-rank and, since 9.x, dense vector search. Solr 10.0 (March 2026) moved to Java 21 and Lucene 10, added quantized vectors and cuVS GPU indexing, and trimmed legacy modules. It fits teams that want fully Apache-licensed, community-run enterprise search and are comfortable running ZooKeeper-backed SolrCloud clusters.

Is Apache Solr open source?

Yes. Apache Solr is open source. License: Apache License 2.0.

Does Apache Solr support ACID transactions?

Partly. Apache Solr offers limited ACID guarantees (for example, single-record or single-partition transactions), with eventual consistency.

Does Apache Solr scale horizontally?

Apache Solr scales horizontally out of the box, with built-in sharding or partitioning. It is comfortable at large scale (≤ 1 PB). It supports cross-region read replicas.

How can I run Apache Solr?

You can self-host it. Managed offerings include SearchStax Managed Search.

What is Apache Solr best for?

Apache Solr is a strong fit for enterprise and intranet search; digital library and publishing search; and E-commerce catalog faceting. Think twice for log analytics at scale.

What are the best alternatives to Apache Solr?

Common alternatives to Apache Solr include Elasticsearch, OpenSearch, Vespa, Manticore Search and Apache Lucene. The right choice depends on your workload, scale and hosting; WhichDB's smart match ranks them against your requirements.

How popular is Apache Solr?

Apache Solr ranks #46 of 844 databases on the WhichDB Score (39.8/100), and #5 among search engine databases. The score combines public adoption signals such as package downloads, GitHub activity, job posts and developer discussion.