Top 4 Java in-memory-database Projects

Apache Ignite

3 4,678 9.5 Java

Apache Ignite (by apache)
microstream

2 554 7.9 Java

High-Performance Java-Native-Persistence. Store and load any Java Object Graph or Subgraphs partially, Relieved of Heavy-weight JPA. Microsecond Response Time. Ultra-High Throughput. Minimum of Latencies. Create Ultra-Fast In-Memory Database Applications & Microservices.

Project mention: Permazen: Language-natural persistence to KV stores | news.ycombinator.com | 2023-09-19

Personally, I found https://microstream.one/ interesting for simple persistance needs (haven't tried it, though).

InfluxDB

www.influxdata.com sponsored

Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
obevo

2 227 0.0 Java

Obevo is a database deployment tool that handles enterprise scale schemas and complexity

Project mention: Working with jOOQ and Flyway using Testcontainers | /r/java | 2023-06-08

The one that does complex stuff (aka super Enterprise) which you would think would be closed source is open source: https://github.com/goldmansachs/obevo

store

1 144 9.2 Java

High-Performance Java-Native-Persistence. Store and load any Java Object Graph or Subgraphs partially, Relieved of Heavy-weight JPA. Microsecond Response Time. Ultra-High Throughput. Minimum of Latencies. Create Ultra-Fast In-Memory Database Applications & Microservices. (by eclipse-store)

Project mention: EclipseStore – Databaseless Java Persistence for Microservices and Serverless | news.ycombinator.com | 2023-12-08

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020).