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Top 23 Java High Performance Projects
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--- ## Step 4 — Choose the Right Pooler for Your Scale | Feature | PgBouncer | pgpool-II | Odyssey | |---|---|---|---| | Transaction mode | ✅ Excellent | ✅ Supported | ✅ Excellent | | Read replica routing | ❌ No | ✅ Built-in | ⚠️ Limited | | Protocol overhead | Very low | Moderate | Low | | Operational complexity | Low | High | Medium | Use PgBouncer for lightweight, high-performance pooling with minimal operational surface area. Use pgpool-II when you need read/write splitting and can absorb the configuration work. Odyssey from Yandex is worth evaluating at very high connection counts — its multi-threaded model handles scale that PgBouncer's single-threaded architecture cannot match above ~50k clients. --- ## Gotchas **`server_reset_query` in transaction mode.** In session mode, PgBouncer runs `DISCARD ALL` between clients. In transaction mode this is skipped — but a custom `server_reset_query` will still fire and break your session state assumptions. **`max_client_conn` lower than your thread count.** If your application has 200 threads but `max_client_conn = 100`, the remaining 100 threads block, timeout, and retry. That retry storm amplifies load exactly when you can least afford it. **No client-side `connect_timeout`.** Without it, blocked connections queue indefinitely. Set `connect_timeout=3000ms` at the pool level, not just at the Postgres level. --- ## Conclusion Most connection storms are self-inflicted through misconfiguration, not load. Audit your ORM's prepared statement behavior first, apply the pool size formula, then deploy PgBouncer with monitoring on `SHOW POOLS` and `SHOW STATS`. Pool saturation should trigger alerts before clients ever see errors. **Resources:** - [PgBouncer documentation](https://www.pgbouncer.org/config.html) - [HikariCP pool sizing analysis](https://github.com/brettwooldridge/HikariCP/wiki/About-Pool-Sizing) - [pgjdbc `preferQueryMode` reference](https://jdbc.postgresql.org/documentation/use/)
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AppSignal
AppSignal knows why the f*#k it crashed. Stop vibe-debugging. Every exception, every backtrace, grouped so you see patterns, not noise.
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Project mention: LMAX Disruptor – High Performance Inter-Thread Messaging Library | news.ycombinator.com | 2026-09-15
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Project mention: Standing on shoulders: the stack that makes Floci start in ~24ms | dev.to | 2026-05-21
Vert.x is the layer where Floci uses things directly. It's Netty with ergonomics: an event loop, a router, protocol-specific APIs for HTTP, DNS, TCP, WebSockets, gRPC, all sharing the same threading model.
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Project mention: Building Metadata Capabilities in Apache SeaTunnel: A Committer’s Journey | dev.to | 2026-05-28
PR Link Description https://github.com/apache/seatunnel/pull/5663 Added save_mode functionality to SeaTunnel https://github.com/apache/seatunnel/pull/10402 Integrated Gravitino with SeaTunnel https://github.com/apache/seatunnel/pull/10586 Designed the metadata SPI interface for SeaTunnel https://github.com/apache/seatunnel/pull/10657 Enhanced the metadata SPI interface for SeaTunnel https://github.com/apache/seatunnel/pull/10838 Added dynamic metadata functionality based on the metadata SPI interface
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Project mention: Crossfire: High-performance lockless spsc/mpsc/mpmc channels for Rust | news.ycombinator.com | 2025-11-01
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Project mention: Tablesaw: Java Dataframe and Visualization Library | news.ycombinator.com | 2026-02-28
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SaaSHub
SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
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Project mention: 100 hour gap between a vibecoded prototype and a working product | news.ycombinator.com | 2026-03-15
In some places I'm using https://github.com/aeron-io/agrona
Strangely this is one of the areas where I want to use project panama so I might re-implement some of the ring buffers constructs.
You allocate off heap memory and dump data into it. With modern Java classes like Arena, MemoryLayout, and VarHandle it's honestly a lot like C structs.
I answered "why" in another post in this thread.
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tlaplus
TLC is a model checker for specifications written in TLA+. The TLA+Toolbox is an IDE for TLA+.
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Eclipse Collections
Eclipse Collections is a collections framework for Java with optimized data structures and a rich, functional and fluent API.
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fastutil
fastutil extends the Java™ Collections Framework by providing type-specific maps, sets, lists and queues.
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GS Collections
GS Collections has been migrated to the Eclipse Foundation, re-branded as Eclipse Collections. https://www.eclipse.org/collections/
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linstor-server
High Performance Software-Defined Block Storage for container, cloud and virtualisation. Fully integrated with Docker, Kubernetes, Openstack, Proxmox etc.
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ActiveJ
ActiveJ is an alternative Java platform built from the ground up. ActiveJ redefines core, web and high-load programming in Java, providing simplicity, maximum performance and scalability
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seatunnel-web
SeaTunnel is a distributed, high-performance data integration platform for the synchronization and transformation of massive data (offline & real-time).
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SaaSHub
SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
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).
Java High Performance discussion
Java High Performance related posts
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PostgreSQL Connection Pooling at Scale
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Cronflower: Turn a Spring Boot app into a distributed cron cluster
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LMAX Disruptor – High Performance Inter-Thread Messaging Library
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Building Metadata Capabilities in Apache SeaTunnel: A Committer’s Journey
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What Happened in Apache SeaTunnel? This March You Shouldn’t Miss
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Connection Pool Exhaustion in Mobile Backends
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Connection Pool Tuning Under Load: How HikariCP Defaults Silently Kill Your Mobile Backend
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A note from our sponsor - AppSignal
www.appsignal.com | 7 Oct 2026
Index
What are some of the best open-source High Performance projects in Java? This list will help you:
| # | Project | Stars |
|---|---|---|
| 1 | HikariCP | 21,228 |
| 2 | Disruptor | 18,480 |
| 3 | Vert.x | 14,692 |
| 4 | seatunnel | 9,697 |
| 5 | fastjson2 | 4,416 |
| 6 | JCTools | 3,876 |
| 7 | Tablesaw | 3,763 |
| 8 | Agrona | 3,255 |
| 9 | tlaplus | 3,104 |
| 10 | Eclipse Collections | 2,653 |
| 11 | fastutil | 2,247 |
| 12 | GS Collections | 1,821 |
| 13 | Rapidoid | 1,633 |
| 14 | linstor-server | 1,295 |
| 15 | Simple Java Mail | 1,291 |
| 16 | DSL-JSON | 1,073 |
| 17 | HPPC | 1,053 |
| 18 | Koloboke | 1,019 |
| 19 | ActiveJ | 997 |
| 20 | cicada | 948 |
| 21 | seatunnel-web | 883 |
| 22 | Zero-Allocation-Hashing | 848 |
| 23 | colfer | 759 |
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