# npgall/cqengine

Ultra-fast SQL-like queries on Java collections

Repository: https://github.com/npgall/cqengine
Canonical: https://ross.abutalabs.com/products/cqengine
Language: Java
License: Apache-2.0
License Family: permissive
Last push: 2023-12-27T20:30:52+00:00

## Health v2 (maintenance only)
Score: 32/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 35, longevity 100
- inputs: {"age_days": 4028, "days_push": 980, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1770, forks 253 (observed 2026-08-28T04:05:33.849906+00:00)

## What it is
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
- artifact type: library
- maturity: stable
- function: database, search-engine, orm
- domain: databases, developer-tools, performance
- platform: jvm
- tags: in-memory-indexing, sql-like-queries, low-latency, java-collections, mvcc, search

## Member repositories
- npgall/cqengine (main) score 32

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:05:33.849906+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T03:26:03.692858+00:00, confidence not recorded.
  - readme: https://github.com/npgall/cqengine (fetched 2026-08-28T04:05:33.849906+00:00, sha 2dac2d4e4c98)
- Data as of 2026-08-30T08:39:29.467469+00:00.