From bbf668d66fbf61d45f1c187b08a5f51537bfb7c7 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Tue, 6 Aug 2024 20:38:33 +0700
Subject: [PATCH] Lower minimum maintenance_work_mem to 64kB
Since the introduction of TID store, vacuum uses far less memory in
the common case than in versions 16 and earlier. Invoking multiple
rounds of index vacuuming in turn requires a much larger table. It'd
be a good idea anyway to cover this case in regression testing, and a
lower limit is less painful for slow buildfarm animals. The reason to
do it now is to re-enable coverage of the bugfix in commit 83c39a1f7f.
For consistency, give autovacuum_work_mem the same treatment.
Suggested by Andres Freund
Tested by Melanie Plageman
Backpatch to v17, where TID store was introduced
Discussion: https://postgr.es/m/20240516205458.ohvlzis5b5tvejru@awork3.anarazel.de
Discussion: https://postgr.es/m/20240722164745.fvaoh6g6zprisqgp%40awork3.anarazel.de
---
src/backend/postmaster/autovacuum.c | 6 +++---
src/backend/utils/misc/guc_tables.c | 7 ++++++-
src/backend/utils/misc/postgresql.conf.sample | 4 ++--
3 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 4e4a0ccbefb..7d0877c95ec 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -3339,12 +3339,12 @@ check_autovacuum_work_mem(int *newval, void **extra, GucSource source)
return true;
/*
- * We clamp manually-set values to at least 1MB. Since
+ * We clamp manually-set values to at least 64kB. Since
* maintenance_work_mem is always set to at least this value, do the same
* here.
*/
- if (*newval < 1024)
- *newval = 1024;
+ if (*newval < 64)
+ *newval = 64;
return true;
}
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index c0a52cdcc3e..289dea7878a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2510,6 +2510,11 @@ struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ /*
+ * Dynamic shared memory has a higher overhead than local memory contexts,
+ * so when testing low-memory scenarios that could use shared memory, the
+ * recommended minimum is 1MB.
+ */
{
{"maintenance_work_mem", PGC_USERSET, RESOURCES_MEM,
gettext_noop("Sets the maximum memory to be used for maintenance operations."),
@@ -2517,7 +2522,7 @@ struct config_int ConfigureNamesInt[] =
GUC_UNIT_KB
},
&maintenance_work_mem,
- 65536, 1024, MAX_KILOBYTES,
+ 65536, 64, MAX_KILOBYTES,
NULL, NULL, NULL
},
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 9ec9f97e926..667e0dc40a2 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -139,8 +139,8 @@
# you actively intend to use prepared transactions.
#work_mem = 4MB # min 64kB
#hash_mem_multiplier = 2.0 # 1-1000.0 multiplier on hash table work_mem
-#maintenance_work_mem = 64MB # min 1MB
-#autovacuum_work_mem = -1 # min 1MB, or -1 to use maintenance_work_mem
+#maintenance_work_mem = 64MB # min 64kB
+#autovacuum_work_mem = -1 # min 64kB, or -1 to use maintenance_work_mem
#logical_decoding_work_mem = 64MB # min 64kB
#max_stack_depth = 2MB # min 100kB
#shared_memory_type = mmap # the default is the first option