From 0dcaea56903489e8abedf231f286272495c3beb4 Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Fri, 26 Jul 2024 15:28:55 -0500 Subject: Introduce num_os_semaphores GUC. The documentation for System V IPC parameters provides complicated formulas to determine the appropriate values for SEMMNI and SEMMNS. Furthermore, these formulas have often been wrong because folks forget to update them (e.g., when adding a new auxiliary process). This commit introduces a new runtime-computed GUC named num_os_semaphores that reports the number of semaphores needed for the configured number of allowed connections, worker processes, etc. This new GUC allows us to simplify the formulas in the documentation, and it should help prevent future inaccuracies. Like the other runtime-computed GUCs, users can view it with "postgres -C" before starting the server, which is useful for preconfiguring the necessary operating system resources. Reviewed-by: Tom Lane, Sami Imseih, Andres Freund, Robert Haas Discussion: https://postgr.es/m/20240517164452.GA1914161%40nathanxps13 --- src/backend/storage/ipc/ipci.c | 6 +++++- src/backend/utils/misc/guc_tables.c | 12 ++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) (limited to 'src') diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c index 2100150f01c..ca930af08f2 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 f6fcdebb031..6a623f5f342 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."), -- cgit v1.2.3