Hi!
I think there's a bug here:
diff --git a/src/backend/postmaster/autovacuum.c
b/src/backend/postmaster/autovacuum.c
index 37998f7387..2ab344c1f8 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -78,6 +78,7 @@
#include "catalog/pg_database.h"
#include "commands/dbcommands.h"
#include "commands/vacuum.h"
+#include "common/int.h"
#include "lib/ilist.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
@@ -1120,10 +1121,8 @@ rebuild_database_list(Oid newdb)
static int
db_comparator(const void *a, const void *b)
{
- if (((const avl_dbase *) a)->adl_score == ((const avl_dbase *)
b)->adl_score)
- return 0;
- else
- return (((const avl_dbase *) a)->adl_score < ((const avl_dbase *)
b)->adl_score) ? 1 : -1;
+ return pg_cmp_s32(((const avl_dbase *) a)->adl_score,
+ ((const avl_dbase *) b)->adl_score);
}
It breaks the database vacuuming order. The order should clearly be different
here.
This bug was introduced in PostgreSQL 17. I have attached а fix.
Best regards,
Rustam Khamidullin, Postgres Professional
From f58198415cf38d8cf29c9d28e77fb9c251a6e951 Mon Sep 17 00:00:00 2001
From: Rustam Khamidullin <[email protected]>
Date: Fri, 24 Jul 2026 11:10:18 +0700
Subject: [PATCH] Fix reversed sort order in autovacuum's db_comparator()
Commit 3b42bdb4716 inadvertently reversed the sort order of databases
in rebuild_database_list(). The original comparator sorted in
descending order by adl_score, but the commit replaced the manual
comparison with pg_cmp_s32(a, b), which produces ascending order.
As a result, the scheduling order of databases for autovacuum was
reversed each time the database list was rebuilt.
Restore the intended descending order by swapping the arguments to
pg_cmp_s32(). Update the surrounding comments to make the expected
sort direction explicit.
---
src/backend/postmaster/autovacuum.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 45abf48768a..e0c2c9b306f 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -1068,7 +1068,10 @@ rebuild_database_list(Oid newdb)
while ((db = hash_seq_search(&seq)) != NULL)
memcpy(&(dbary[i++]), db, sizeof(avl_dbase));
- /* sort the array */
+ /*
+ * Sort the array in descending order so that the databases with the
+ * highest score get the least adl_next_worker time.
+ */
qsort(dbary, nelems, sizeof(avl_dbase), db_comparator);
/*
@@ -1109,12 +1112,12 @@ rebuild_database_list(Oid newdb)
MemoryContextSwitchTo(oldcxt);
}
-/* qsort comparator for avl_dbase, using adl_score */
+/* qsort comparator for avl_dbase, using adl_score in descending order */
static int
db_comparator(const void *a, const void *b)
{
- return pg_cmp_s32(((const avl_dbase *) a)->adl_score,
- ((const avl_dbase *) b)->adl_score);
+ return pg_cmp_s32(((const avl_dbase *) b)->adl_score,
+ ((const avl_dbase *) a)->adl_score);
}
/*
--
2.54.0
