Horton

Re: Estimating HugePages Requirements?

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Magnus Hagander <magnus@hagander.net>
Cc: Julien Rouhaud <rjuju123@gmail.com>, Don Seiler <don@seiler.us>, pgsql-admin <pgsql-admin@postgresql.org>
Date: 2021-06-09T19:15:37Z
Lists: pgsql-hackers 
Magnus Hagander <magnus@hagander.net> writes:
> I wonder how hard it would be to for example expose that through a
> commandline switch or tool.

Just try to start the server and see if it complains.
For instance, with shared_buffers=10000000 I get

2021-06-09 15:08:56.821 EDT [1428121] FATAL:  could not map anonymous shared memory: Cannot allocate memory
2021-06-09 15:08:56.821 EDT [1428121] HINT:  This error usually means that PostgreSQL's request for a shared memory segment exceeded available memory, swap space, or huge pages. To reduce the request size (currently 83720568832 bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing shared_buffers or max_connections.

Of course, if it *does* start, you can do the other thing.

Admittedly, we could make that easier somehow; but if it took
25 years for somebody to ask for this, I'm not sure it's
worth creating a feature to make it a shade easier.

			regards, tom lane

Commits

  1. Silence extra logging when using "postgres -C" on runtime-computed GUCs

  2. doc: Improve postgres command for shared_memory_size_in_huge_pages

  3. Introduce GUC shared_memory_size_in_huge_pages

  4. Support "postgres -C" with runtime-computed GUCs

  5. Make shared_memory_size a preset option

  6. Introduce GUC shared_memory_size

  7. Move the shared memory size calculation to its own function

  8. Add new GUC, max_worker_processes, limiting number of bgworkers.