Horton

Re: Estimating HugePages Requirements?

Nathan Bossart <bossartn@amazon.com>

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From: "Bossart, Nathan" <bossartn@amazon.com>
To: Andres Freund <andres@anarazel.de>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, Don Seiler <don@seiler.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2021-08-11T23:23:52Z
Lists: pgsql-hackers

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On 8/9/21, 8:43 PM, "Andres Freund" <andres@anarazel.de> wrote:
> I don't like putting this into PostmasterMain(). Either BootstrapMain()
> (specifically checker mode) or GucInfoMain() seem like better places.

I think BootstrapModeMain() makes the most sense.  It fits in nicely
with the --check logic that's already there.  With v3, the following
command can be used to retrieve the amount of shared memory required.

        postgres --output-shmem -D dir

While testing this new option, I noticed that you can achieve similar
results today with the following command, although this one will
actually try to create the shared memory, too.

        postgres --check -D dir -c log_min_messages=debug3 2> >(grep IpcMemoryCreate)

IMO the new option is still handy, but I can see the argument that it
might not be necessary.

> That seems like an ugly API to me. Why don't we split the size
> determination and shmem creation functions into two?

I did it this way in v3.

Nathan

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.