diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3dec0b7cfe..57cd7bb972 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -11145,6 +11145,24 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
+
+ num_os_semaphores (integer)
+
+ num_os_semaphores configuration parameter
+
+
+
+
+ Reports the number of semaphores that are needed for the server based
+ on the configured number of allowed connections
+ (), allowed autovacuum worker
+ processes (), allowed WAL
+ sender processes (), allowed
+ background processes (), etc.
+
+
+
+
segment_size (integer)
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 2f7c618886..2c4d5ef640 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -781,13 +781,13 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
SEMMNI
Maximum number of semaphore identifiers (i.e., sets)
- at least ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 7) / 16) plus room for other applications
+ at least ceil(num_os_semaphores / 16) plus room for other applications
SEMMNS
Maximum number of semaphores system-wide
- ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 7) / 16) * 17 plus room for other applications
+ ceil(num_os_semaphores / 16) * 17 plus room for other applications
@@ -839,21 +839,28 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
PostgreSQL uses one semaphore per allowed connection
(), allowed autovacuum worker process
(), allowed WAL sender process
- (), and allowed background
- process (), in sets of 16.
- Each such set will
+ (), allowed background
+ process (), etc., in sets of 16.
+ The runtime-computed parameter
+ reports the number of semaphores required. This parameter can be viewed
+ before starting the server with a postgres command like:
+
+$ postgres -D $PGDATA -C num_os_semaphores
+
+
+
+
+ Each set of 16 semaphores will
also contain a 17th semaphore which contains a magic
number
, to detect collision with semaphore sets used by
other applications. The maximum number of semaphores in the system
is set by SEMMNS, which consequently must be at least
- as high as max_connections plus
- autovacuum_max_workers plus max_wal_senders,
- plus max_worker_processes, plus one extra for each 16
- allowed connections plus workers (see the formula in num_os_semaphores plus one extra for
+ each set of 16 required semaphores (see the formula in ). The parameter SEMMNI
determines the limit on the number of semaphore sets that can
exist on the system at one time. Hence this parameter must be at
- least ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 7) / 16).
+ least ceil(num_os_semaphores / 16).
Lowering the number
of allowed connections is a temporary workaround for failures,
which are usually confusingly worded No space
@@ -885,8 +892,8 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
same as for System V, that is one semaphore per allowed connection
(), allowed autovacuum worker process
(), allowed WAL sender process
- (), and allowed background
- process ().
+ (), allowed background
+ process (), etc.
On the platforms where this option is preferred, there is no specific
kernel limit on the number of POSIX semaphores.
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2100150f01..ca930af08f 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -372,11 +372,12 @@ InitializeShmemGUCs(void)
Size size_b;
Size size_mb;
Size hp_size;
+ int num_semas;
/*
* Calculate the shared memory size and round up to the nearest megabyte.
*/
- size_b = CalculateShmemSize(NULL);
+ size_b = CalculateShmemSize(&num_semas);
size_mb = add_size(size_b, (1024 * 1024) - 1) / (1024 * 1024);
sprintf(buf, "%zu", size_mb);
SetConfigOption("shared_memory_size", buf,
@@ -395,4 +396,7 @@ InitializeShmemGUCs(void)
SetConfigOption("shared_memory_size_in_huge_pages", buf,
PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
}
+
+ sprintf(buf, "%d", num_semas);
+ SetConfigOption("num_os_semaphores", buf, PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
}
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index f6fcdebb03..6a623f5f34 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -591,6 +591,7 @@ static int segment_size;
static int shared_memory_size_mb;
static int shared_memory_size_in_huge_pages;
static int wal_block_size;
+static int num_os_semaphores;
static bool data_checksums;
static bool integer_datetimes;
@@ -2283,6 +2284,17 @@ struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ {
+ {"num_os_semaphores", PGC_INTERNAL, PRESET_OPTIONS,
+ gettext_noop("Shows the number of semaphores required for the server."),
+ NULL,
+ GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_RUNTIME_COMPUTED
+ },
+ &num_os_semaphores,
+ 0, 0, INT_MAX,
+ NULL, NULL, NULL
+ },
+
{
{"commit_timestamp_buffers", PGC_POSTMASTER, RESOURCES_MEM,
gettext_noop("Sets the size of the dedicated buffer pool used for the commit timestamp cache."),