Re: [PATCH] Assertion in pg_get_shmem_pagesize() in single-user mode

On 21/09/2026 02:51, Ayush Tiwari wrote:
> While trying pg_buffercache in single-user mode, I noticed what looks
> like an overly restrictive assertion in pg_get_shmem_pagesize(). With
> pg_buffercache installed and the server stopped, I can reproduce this
> on an assertion-enabled build:
>
> $ postgres --single -D "$PGDATA" postgres
> backend> SELECT pg_buffercache_os_pages(false) LIMIT 1;
> TRAP: failed Assert("IsUnderPostmaster")
>
> AFAICS, PostgresSingleUserMain() calls
> CreateSharedMemoryAndSemaphores() before processing queries, so
> huge_pages_status should already be initialized at this point.
> However, IsUnderPostmaster is false in a standalone backend.
>
> Could we drop that assertion and retain the existing
> Assert(huge_pages_status != HUGE_PAGES_UNKNOWN)? That seems to check
> the relevant precondition without excluding single-user mode. This
> also doesn't appear specific to NUMA, since the query above requests
> only OS-page mappings.

Agreed.

> The attached patch removes the process-role assertion and adjusts the
> comment to refer to shared-memory creation. The query seems to work
> with this change in my local testing.
>
> Does this look reasonable, or am I overlooking another reason for
> the IsUnderPostmaster check?

+1. Committed, thanks!

- Heikki