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Fix shmem allocation of fixed-sized custom stats kind

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StatsShmemSize(), that computes the shmem size needed for pgstats,
includes the amount of shared memory wanted by all the custom stats
kinds registered.  However, the shared memory allocation was done by
ShmemAlloc() in StatsShmemInit(), meaning that the space reserved was
not used, wasting some memory.

These extra allocations would show up under "<anonymous>" in
pg_shmem_allocations, as the allocations done by ShmemAlloc() are not
tracked by ShmemIndexEnt.

Issue introduced by 7949d95945.

Author: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/04b04387-92f5-476c-90b0-4064e71c5f37@iki.fi
Backpatch-through: 18
This commit is contained in:
Michael Paquier 2026-04-07 11:59:49 +09:00
parent 5c54c3ed1b
commit 17132f55c5
1 changed files with 4 additions and 3 deletions
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7
src/backend/utils/activity/pgstat_shmem.c
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@ -150,8 +150,7 @@ StatsShmemSize(void)
continue;
Assert(kind_info->shared_size != 0);
sz += MAXALIGN(kind_info->shared_size);
sz = add_size(sz, MAXALIGN(kind_info->shared_size));
}
return sz;
@ -189,6 +188,7 @@ StatsShmemInit(void *arg)
* efficiency win.
*/
ctl->raw_dsa_area = p;
p += pgstat_dsa_init_size();
dsa = dsa_create_in_place(ctl->raw_dsa_area,
pgstat_dsa_init_size(),
LWTRANCHE_PGSTATS_DSA, NULL);
@ -242,7 +242,8 @@ StatsShmemInit(void *arg)
int idx = kind - PGSTAT_KIND_CUSTOM_MIN;
Assert(kind_info->shared_size != 0);
ctl->custom_data[idx] = ShmemAlloc(kind_info->shared_size);
ctl->custom_data[idx] = p;
p += MAXALIGN(kind_info->shared_size);
ptr = ctl->custom_data[idx];
}