doc: Worker and heap usage

[ronag]

I would like to request some clarification on the docs in regards to workers and heap usage in particular when setting memory limits.

e.g. we have a Node service running in a docker container with a memory limit of 1G. We set the --max-old-space-size to =768. However, the node service will spawn 16 worker threads. Will these threads share old space size with the main process or do they all have their own heaps with e.g. 768M which gives a global heap size of 17 * 768 = 13 056M and getting itself killed by the OOM killer.

Also how do the rules apply to child processes and inheritance of old-space-size settings?

[sam-github]

• node workers: no idea
• cluster workers: arg is passed to the child processes, all the processes will (possibly) use the full max space simultaneously
• child_process children: arg will not be passed unless the code spawning the child does so explicitly, all the processes will (possibly) use the full max space (as they may or may not have received on their command line) simultaneously

EDIT: this may be a good reason to use NODE_OPTIONS to set the max space, it is inherited by all child processes automatically (unless they modify the env), but only node children will actually pay attention to it

[addaleax]

@ronag worker_threads workers will have their own independent heaps. I’ll try to pick up work on #26628 again this week, fwiw.

[ronag]

@addaleax: Cool, we'll wait for that before switching to threads from child processes.

[gireeshpunathil]

17 * 768 = 13 056M and getting itself killed by the OOM killer.

@ronag - My colleague and I have experimented a bit on this topic and have some findings captured here - not necessarily on the choice between threads and processes, but the perceived and actual relationship between heap size and the OOM killer function. Hope this helps you in some way:

https://medium.com/the-node-js-collection/node-js-memory-management-in-container-environments-7eb8409a74e8

[gireeshpunathil]

closing this as #26628 is landed and with the clarification. Please re-open if there is anything outstanding on this