spark is a performance profiling plugin/mod for Minecraft clients, servers and proxies.
#### Useful Links
* [**Website**](https://spark.lucko.me/) - browse the project homepage
* [**Documentation**](https://spark.lucko.me/docs) - read documentation and usage guides
* [**Downloads**](https://spark.lucko.me/download) - latest plugin/mod downloads
## What does spark do?
spark is made up of three separate components:
| CPU Profiler | Memory Inspection | Server Health Reporting |
| :-------------------------------------------: | :--------------------------------------: | :----------------------------------------: |
| [](#zap-cpu-profiler) | [](#zap-memory-inspection) | [](#zap-server-health-reporting) |
| Diagnose performance issues. | Diagnose memory issues. | Keep track of overall server health. |
### :zap: CPU Profiler
spark's profiler can be used to diagnose performance issues: "lag", low tick rate, high CPU usage, etc.
It is:
* **Lightweight** - can be ran in production with minimal impact.
* **Easy to use** - no configuration or setup necessary, just install the plugin/mod.
* **Quick to produce results** - running for just ~30 seconds is enough to produce useful insights into problematic areas for performance.
* **Customisable** - can be tuned to target specific threads, sample at a specific interval, record only "laggy" periods, etc
* **Highly readable** - simple tree structure lends itself to easy analysis and interpretation. The viewer can also apply deobfuscation mappings.
It works by sampling statistical data about the systems activity, and constructing a call graph based on this data. The call graph is then displayed in an online viewer for further analysis by the user.
There are two different profiler engines:
* Native `AsyncGetCallTrace` + `perf_events` - uses [async-profiler](https://github.com/jvm-profiling-tools/async-profiler) (*only available on Linux x86_64 systems*)
* Built-in Java `ThreadMXBean` - an improved version of the popular [WarmRoast profiler](https://github.com/sk89q/WarmRoast) by sk89q.
### :zap: Memory Inspection
spark includes a number of tools which are useful for diagnosing memory issues with a server.
* **Heap Summary** - take & analyse a basic snapshot of the servers memory
* A simple view of the JVM's heap, see memory usage and instance counts for each class
* Not intended to be a full replacement of proper memory analysis tools. (see next item)
* **Heap Dump** - take a full (HPROF) snapshot of the servers memory
* Dumps (& optionally compresses) a full snapshot of JVM's heap.
* This snapshot can then be inspected using conventional analysis tools.
* **GC Monitoring** - monitor garbage collection activity on the server
* Allows the user to relate GC activity to game server hangs, and easily see how long they are taking & how much memory is being free'd.
* Observe frequency/duration of young/old generation garbage collections to inform which GC tuning flags to use
### :zap: Server Health Reporting
spark can report a number of metrics summarising the servers overall health.
These metrics include:
* **TPS** - ticks per second, to a more accurate degree indicated by the /tps command
* **Tick Durations** - how long each tick is taking (min, max and average)
* **CPU Usage** - how much of the CPU is being used by the process, and by the overall system
* **Memory Usage** - how much memory is being used by the process
* **Disk Usage** - how much disk space is free/being used by the system
As well as providing tick rate averages, spark can also **monitor individual ticks** - sending a report whenever a single tick's duration exceeds a certain threshold. This can be used to identify trends and the nature of performance issues, relative to other system or game events.
For a comparison between spark, WarmRoast, Minecraft timings and other profiles, see this [page](https://spark.lucko.me/docs/misc/spark-vs-others) in the spark docs.
## License
spark is free & open source. It is released under the terms of the GNU GPLv3 license. Please see [`LICENSE.txt`](LICENSE.txt) for more information.
The spark API submodule is released under the terms of the more permissive MIT license. Please see [`spark-api/LICENSE.txt`](spark-api/LICENSE.txt) for more information.
spark is a fork of [WarmRoast](https://github.com/sk89q/WarmRoast), which was also [licensed using the GPLv3](https://github.com/sk89q/WarmRoast/blob/3fe5e5517b1c529d95cf9f43fd8420c66db0092a/src/main/java/com/sk89q/warmroast/WarmRoast.java#L1-L17).