Re: pgsql: Introduce pg_shmem_allocations_numa view

From: Christoph Berg <myon(at)debian(dot)org>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Tomas Vondra <tomas(dot)vondra(at)postgresql(dot)org>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: pgsql: Introduce pg_shmem_allocations_numa view
Date: 2025-06-23 19:57:56
Message-ID: aFmxxHVS9XwbQ_em@msg.df7cb.de
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Re: Andres Freund
> How confident are we that this isn't actually because we passed a bogus
> address to the kernel or such? With this patch, are *any* pages recognized as
> valid on the machines that triggered the error?

See upthread - the first 35 pages were ok, then a lot of -14.

> I wonder if we ought to report the failures as a separate "numa node"
> (e.g. NULL as node id) instead ...

Did that now, using N+1 (== 1 here) for errors in this Debian i386
environment (chroot on an amd64 host):

select * from pg_shmem_allocations_numa \crosstabview

name │ 0 │ 1
────────────────────────────────────────────────┼──────────┼──────────
multixact_offset │ 69632 │ 65536
subtransaction │ 139264 │ 131072
notify │ 139264 │ 0
Shared Memory Stats │ 188416 │ 131072
serializable │ 188416 │ 86016
PROCLOCK hash │ 4096 │ 0
FinishedSerializableTransactions │ 4096 │ 0
XLOG Ctl │ 2117632 │ 2097152
Shared MultiXact State │ 4096 │ 0
Proc Header │ 4096 │ 0
Archiver Data │ 4096 │ 0
.... more 0s in the last column ...
AioHandleData │ 1429504 │ 0
Buffer Blocks │ 67117056 │ 67108864
Buffer IO Condition Variables │ 266240 │ 0
Proc Array │ 4096 │ 0
.... more 0s
(73 rows)

There is something fishy with pg_buffercache. If I restart PG, I'm
getting "Bad address" (errno 14), this time as return value of
move_pages().

postgres =# select * from pg_buffercache_numa;
DEBUG: 00000: NUMA: NBuffers=16384 os_page_count=32768 os_page_size=4096
LOCATION: pg_buffercache_numa_pages, pg_buffercache_pages.c:383
2025-06-23 19:41:41.315 UTC [1331894] ERROR: failed NUMA pages inquiry: Bad address
2025-06-23 19:41:41.315 UTC [1331894] STATEMENT: select * from pg_buffercache_numa;
ERROR: XX000: failed NUMA pages inquiry: Bad address
LOCATION: pg_buffercache_numa_pages, pg_buffercache_pages.c:394

Repeated calls are fine.

Maybe NUMA is just not supported on 32-bit archs, but I'd rather be
sure about that before play that card.

Christoph

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