While working on an idea from another thread [0], I noticed that each of
max_connections, max_worker_process, max_autovacuum_workers, and
max_wal_senders have a check hook that verifies the sum of those GUCs does
not exceed a certain value. Then, in InitializeMaxBackends(), we do the
same check once more. Not only do the check hooks seem redundant, but I
think they might sometimes be inaccurate since some values might not yet be
initialized. Furthermore, the error message is not exactly the most
descriptive:
$ pg_ctl -D . start -o "-c max_connections=262100 -c
max_wal_senders=10000"
FATAL: invalid value for parameter "max_wal_senders": 10000
The attached patch removes these hooks and enhances the error message to
look like this:
FATAL: too many backends configured
DETAIL: "max_connections" (262100) plus "autovacuum_max_workers" (3)
plus "max_worker_processes" (8) plus "max_wal_senders" (10000) must be less
than 262142.
The downside of this change is that server startup progresses a little
further before it fails, but that might not be too concerning given this
_should_ be a relatively rare occurrence.
Thoughts?
[0] https://postgr.es/m/20240618213331.ef2spg3nasksisbi%40awork3.anarazel.de
--
nathan
>From 2ab34581879d2122f03be0e3f9d0d15edb501a7c Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nat...@postgresql.org>
Date: Wed, 19 Jun 2024 13:39:18 -0500
Subject: [PATCH v1 1/1] remove check hooks for GUCs that contribute to
MaxBackends
---
src/backend/utils/init/postinit.c | 57 ++++-------------------------
src/backend/utils/misc/guc_tables.c | 8 ++--
src/include/utils/guc_hooks.h | 6 ---
3 files changed, 11 insertions(+), 60 deletions(-)
diff --git a/src/backend/utils/init/postinit.c
b/src/backend/utils/init/postinit.c
index 0805398e24..8a629982c4 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -580,57 +580,14 @@ InitializeMaxBackends(void)
MaxBackends = MaxConnections + autovacuum_max_workers + 1 +
max_worker_processes + max_wal_senders;
- /* internal error because the values were all checked previously */
if (MaxBackends > MAX_BACKENDS)
- elog(ERROR, "too many backends configured");
-}
-
-/*
- * GUC check_hook for max_connections
- */
-bool
-check_max_connections(int *newval, void **extra, GucSource source)
-{
- if (*newval + autovacuum_max_workers + 1 +
- max_worker_processes + max_wal_senders > MAX_BACKENDS)
- return false;
- return true;
-}
-
-/*
- * GUC check_hook for autovacuum_max_workers
- */
-bool
-check_autovacuum_max_workers(int *newval, void **extra, GucSource source)
-{
- if (MaxConnections + *newval + 1 +
- max_worker_processes + max_wal_senders > MAX_BACKENDS)
- return false;
- return true;
-}
-
-/*
- * GUC check_hook for max_worker_processes
- */
-bool
-check_max_worker_processes(int *newval, void **extra, GucSource source)
-{
- if (MaxConnections + autovacuum_max_workers + 1 +
- *newval + max_wal_senders > MAX_BACKENDS)
- return false;
- return true;
-}
-
-/*
- * GUC check_hook for max_wal_senders
- */
-bool
-check_max_wal_senders(int *newval, void **extra, GucSource source)
-{
- if (MaxConnections + autovacuum_max_workers + 1 +
- max_worker_processes + *newval > MAX_BACKENDS)
- return false;
- return true;
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("too many backends configured"),
+ errdetail("\"max_connections\" (%d) plus
\"autovacuum_max_workers\" (%d) plus \"max_worker_processes\" (%d) plus
\"max_wal_senders\" (%d) must be less than %d.",
+ MaxConnections,
autovacuum_max_workers,
+ max_worker_processes,
max_wal_senders,
+ MAX_BACKENDS - 1)));
}
/*
diff --git a/src/backend/utils/misc/guc_tables.c
b/src/backend/utils/misc/guc_tables.c
index 46c258be28..07b575894d 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2207,7 +2207,7 @@ struct config_int ConfigureNamesInt[] =
},
&MaxConnections,
100, 1, MAX_BACKENDS,
- check_max_connections, NULL, NULL
+ NULL, NULL, NULL
},
{
@@ -2923,7 +2923,7 @@ struct config_int ConfigureNamesInt[] =
},
&max_wal_senders,
10, 0, MAX_BACKENDS,
- check_max_wal_senders, NULL, NULL
+ NULL, NULL, NULL
},
{
@@ -3153,7 +3153,7 @@ struct config_int ConfigureNamesInt[] =
},
&max_worker_processes,
8, 0, MAX_BACKENDS,
- check_max_worker_processes, NULL, NULL
+ NULL, NULL, NULL
},
{
@@ -3387,7 +3387,7 @@ struct config_int ConfigureNamesInt[] =
},
&autovacuum_max_workers,
3, 1, MAX_BACKENDS,
- check_autovacuum_max_workers, NULL, NULL
+ NULL, NULL, NULL
},
{
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index d64dc5fcdb..6304f0679b 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -29,8 +29,6 @@ extern bool check_application_name(char **newval, void
**extra,
GucSource
source);
extern void assign_application_name(const char *newval, void *extra);
extern const char *show_archive_command(void);
-extern bool check_autovacuum_max_workers(int *newval, void **extra,
-
GucSource source);
extern bool check_autovacuum_work_mem(int *newval, void **extra,
GucSource source);
extern bool check_vacuum_buffer_usage_limit(int *newval, void **extra,
@@ -84,13 +82,9 @@ extern const char *show_log_timezone(void);
extern bool check_maintenance_io_concurrency(int *newval, void **extra,
GucSource source);
extern void assign_maintenance_io_concurrency(int newval, void *extra);
-extern bool check_max_connections(int *newval, void **extra, GucSource source);
-extern bool check_max_wal_senders(int *newval, void **extra, GucSource source);
extern bool check_max_slot_wal_keep_size(int *newval, void **extra,
GucSource source);
extern void assign_max_wal_size(int newval, void *extra);
-extern bool check_max_worker_processes(int *newval, void **extra,
-
GucSource source);
extern bool check_max_stack_depth(int *newval, void **extra, GucSource source);
extern void assign_max_stack_depth(int newval, void *extra);
extern bool check_multixact_member_buffers(int *newval, void **extra,
--
2.39.3 (Apple Git-146)
