Horton

Re: Estimating HugePages Requirements?

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, Don Seiler <don@seiler.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2021-08-10T03:42:05Z
Lists: pgsql-hackers 
Hi,

On 2021-08-09 22:57:18 +0000, Bossart, Nathan wrote:

> @@ -1026,6 +1031,18 @@ PostmasterMain(int argc, char *argv[])
>  	 */
>  	InitializeMaxBackends();
>  
> +	if (output_shmem)
> +	{
> +		char output[64];
> +		Size size;
> +
> +		size = CreateSharedMemoryAndSemaphores(true);
> +		sprintf(output, "%zu", size);
> +
> +		puts(output);
> +		ExitPostmaster(0);
> +	}

I don't like putting this into PostmasterMain(). Either BootstrapMain()
(specifically checker mode) or GucInfoMain() seem like better places.


> -void
> -CreateSharedMemoryAndSemaphores(void)
> +Size
> +CreateSharedMemoryAndSemaphores(bool size_only)
>  {
>  	PGShmemHeader *shim = NULL;
>  
> @@ -161,6 +161,9 @@ CreateSharedMemoryAndSemaphores(void)
>  		/* might as well round it off to a multiple of a typical page size */
>  		size = add_size(size, 8192 - (size % 8192));
>  
> +		if (size_only)
> +			return size;
> +
>  		elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
>  
>  		/*
> @@ -288,4 +291,6 @@ CreateSharedMemoryAndSemaphores(void)
>  	 */
>  	if (shmem_startup_hook)
>  		shmem_startup_hook();
> +
> +	return 0;
>  }

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


Greetings,

Andres Freund

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.