# Go memory watchdog

> 🐺 A library to curb OOMs by running Go GC according to a user-defined policy.

go-watchdog runs a singleton memory watchdog. It takes system and heap memory
readings periodically, and feeds them to a user-defined policy to determine
whether GC needs to run immediately.

This library ships with two policies out of the box:

* watermarks policy: runs GC at configured watermarks of system or heap memory
  utilisation.
* adaptive: runs GC when the current usage surpasses a dynamically-set
  threshold.
  
You can easily build a custom policy tailored to the allocation patterns of your
program.

It is recommended that you set both (a) a memory limit and (b) a scope of
application of that limit (system or heap) when you start the watchdog.
Otherwise, go-watchdog will use the system scope, and will default to the
total system memory as the limit. [elastic/go-sigar](https://github.com/elastic/gosigar)
is used to make the discovery.

## Why is this even needed?

The garbage collector that ships with the go runtime is pretty good in some
regards (low-latency, negligible no stop-the-world), but it's insatisfactory in
a number of situations that yield ill-fated outcomes:

1. it is incapable of dealing with bursty/spiky allocations efficiently;
   depending on the workload, the program may OOM as a consequence of not
   scheduling GC in a timely manner.
2. part of the above is due to the fact that go doesn't concern itself with any
   limits. To date, it is not possible to set a maximum heap size. 
2. its default policy of scheduling GC when the heap doubles, coupled with its
   ignorance of system or process limits, can easily cause it to OOM.

For more information, check out these GitHub issues:

* https://github.com/golang/go/issues/42805
* https://github.com/golang/go/issues/42430
* https://github.com/golang/go/issues/14735
* https://github.com/golang/go/issues/16843
* https://github.com/golang/go/issues/10064
* https://github.com/golang/go/issues/9849

## License

Dual-licensed: [MIT](./LICENSE-MIT), [Apache Software License v2](./LICENSE-APACHE), by way of the
[Permissive License Stack](https://protocol.ai/blog/announcing-the-permissive-license-stack/).