npgall/cqengine

Health v2 · maintenance only

Flags: no_releases

Adoption not part of the score

1770 stars · 253 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

CQEngine (Collection Query Engine) is a high-performance Java library that allows SQL-like queries to be executed against Java collections using indexes, achieving microsecond query latencies and millions of queries per second. It supports on-heap, off-heap, and disk persistence with MVCC transaction isolation, letting applications offload query traffic from databases.

Use cases

• query java collections with sql-like syntax
• index objects in memory for fast retrieval
• offload read queries from the database to the application tier
• run low-latency range and filter queries on large datasets
• replace slow iteration over collections with indexed lookups
• build an in-memory query engine with disk persistence

When to choose

• you need microsecond-latency queries over in-memory Java objects
• your database read traffic can be offloaded to the application tier
• you want indexed queries on collections without running a database server
• you need MVCC transaction isolation over indexed collections

When to avoid

• you need full SQL features like joins across tables or a query planner
• your dataset does not fit in memory or local disk
• you need multi-client network access to the data store
• your team prefers standard ORM or database tooling

Facets

library · maturity stable

database search-engine orm databases developer-tools performance jvm in-memory-indexing sql-like-queries low-latency java-collections mvcc search

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