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

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 4e4a0ccbefbedda9bd7b763de54311c69f553f74..7d0877c95ec87cbc46bd5ca89443c033cd16127e 100644 (file)
--- 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 c0a52cdcc3ed24b5d2810a0eaf3430ac256b6968..289dea7878a6dbb2e932e56ffcbd4cf9e5aba060 100644 (file)
--- 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 9ec9f97e926dc08fa5ec4f7b31e860679f8ea7f7..667e0dc40a24f72ee7b4c02a13b7d7798c5888a6 100644 (file)
--- 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