Memory leaks in long-running processes

[mfornos]

It's known that using the Polkadot.js API library in long-running processes, such as on a Node.js backend, results in increasing memory consumption until the process crashes due to memory leaks.

Below is a summary of the major memory leaks and how to fix them:

1. Well-known memory leak in @polkadot/rpc-core storage cache:
   Memory leak in ApiPromise timers #5674 (comment)
   Patch: Link

2. Function memoization used across the library via the memo utility:
   

   api/packages/rpc-core/src/util/memo.ts

   Line 20 in 87bee8a

   export function memo <T> (instanceId: string, inner: Function): Memoized<ObsFn<T>> {

   
   Further investigation is needed to identify the leaky usage. As a quick fix, patch the memoize function in @polkadot/util:
   Patch: Link

3. LRU cache in @polkadot/rpc-provider:
   The custom LRU cache implementation is not being properly evicted. Supposedly fixed in Fix LRUCache memory leak. #4520, but it still leaks in long-running processes. As a workaround, disable the cache:
   Patch: Link

Applying these patches will significantly reduce memory consumption and help maintain a stable footprint for your Node.js long-running processes using Polkadot.js.

We would like to investigate these issues in more detail, but due to other priorities, we currently don't have the time.

[TarikGul]

Thanks for all the info above, that is super helpful!

cc: @filvecchiato (Since he has been working closely with performance issues in sidecar and PJS recently).

I think this is definitely something we can tackle very soon and get to the bottom of.