From 810a8b1c8051d4e8822967a96f133692698386de Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 29 Apr 2025 17:27:52 -0400 Subject: [PATCH] Give up on running with NetBSD/OpenBSD's default semaphore settings. This reverts commit 38da053463bef32adf563ddee5277d16d2b6c5af, which attempted to preserve our ability to start with only 60 semaphores. Subsequent changes (particularly 55b454d0e) have put that idea pretty much permanently out of reach: people wishing to use Postgres v18 on OpenBSD or NetBSD will have no choice but to increase those platforms' default values of SEMMNI and SEMMNS. Hence, revert 38da05346's changes in SEMAS_PER_SET and the minimum tested value of max_connections. Adjust a comment from the subsequent patch 6d0154196, and tweak the wording in runtime.sgml to make it clear that changing SEMMNI/SEMMNS is no longer even a little bit optional on these platforms. Although 38da05346 was later back-patched into v17, leave that branch alone: it's still capable of starting with 60 semaphores, and there's no reason to break that. Author: Tom Lane Reviewed-by: Nathan Bossart Discussion: https://postgr.es/m/E1tuZNv-0037Gs-34@gemulon.postgresql.org Discussion: https://postgr.es/m/1052019.1745947915@sss.pgh.pa.us --- doc/src/sgml/runtime.sgml | 24 ++++++++++++------------ src/backend/port/sysv_sema.c | 8 +------- src/bin/initdb/initdb.c | 9 ++++----- 3 files changed, 17 insertions(+), 24 deletions(-) diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index 3a6d308ae35..0c60bafac63 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -782,19 +782,19 @@ 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(num_os_semaphores / 19) 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(num_os_semaphores / 19) * 20 plus room for other applications + ceil(num_os_semaphores / 16) * 17 plus room for other applications SEMMSL Maximum number of semaphores per set - at least 20 + at least 17 @@ -841,7 +841,7 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such (), allowed autovacuum worker process (), allowed WAL sender process (), allowed background - process (), etc., in sets of 19. + 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: @@ -851,17 +851,17 @@ $ postgres -D $PGDATA -C num_os_semaphores - Each set of 19 semaphores will - also contain a 20th semaphore which contains a magic + 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 num_os_semaphores plus one extra for - each set of 19 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(num_os_semaphores / 19). + 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 @@ -953,10 +953,10 @@ $ postgres -D $PGDATA -C num_os_semaphores The default shared memory settings are usually good enough, unless you have set shared_memory_type to sysv. - You will usually want to increase kern.ipc.semmni + However, you will need to increase kern.ipc.semmni and kern.ipc.semmns, as NetBSD's default settings - for these are uncomfortably small. + for these are unworkably small. @@ -987,11 +987,11 @@ $ postgres -D $PGDATA -C num_os_semaphores The default shared memory settings are usually good enough, unless you have set shared_memory_type to sysv. - You will usually want to + However, you will need to increase kern.seminfo.semmni and kern.seminfo.semmns, as OpenBSD's default settings - for these are uncomfortably small. + for these are unworkably small. diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c index f7c8638aec5..423b2b4f9d6 100644 --- a/src/backend/port/sysv_sema.c +++ b/src/backend/port/sysv_sema.c @@ -50,14 +50,8 @@ typedef int IpcSemaphoreId; /* semaphore ID returned by semget(2) */ * we allocate. It must be *less than* your kernel's SEMMSL (max semaphores * per set) parameter, which is often around 25. (Less than, because we * allocate one extra sema in each set for identification purposes.) - * - * The present value of 19 is chosen with one eye on NetBSD/OpenBSD's default - * SEMMNS setting of 60. Remembering the extra sema per set, this lets us - * allocate three sets with 57 useful semaphores before exceeding that, which - * is enough to run our core regression tests. Users of those systems will - * still want to raise SEMMNS for any sort of production work, though. */ -#define SEMAS_PER_SET 19 +#define SEMAS_PER_SET 16 #define IPCProtection (0600) /* access/modify by user only */ diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c index aefe8130a68..62bbd08d9f6 100644 --- a/src/bin/initdb/initdb.c +++ b/src/bin/initdb/initdb.c @@ -1128,15 +1128,14 @@ test_config_settings(void) * for a given max_connections value. Note that it has been carefully * crafted to provide specific values for the associated values in * trial_conns. We want it to return autovacuum_worker_slots's initial - * default value (16) for the maximum value in trial_conns (100), and we - * want it to return close to the minimum value we'd consider (3, which is - * the default of autovacuum_max_workers) for the minimum value in - * trial_conns (25). + * default value (16) for the maximum value in trial_conns[] (100), while + * it mustn't return less than the default value of autovacuum_max_workers + * (3) for the minimum value in trial_conns[]. */ #define AV_SLOTS_FOR_CONNS(nconns) ((nconns) / 6) static const int trial_conns[] = { - 100, 50, 40, 30, 25 + 100, 50, 40, 30, 20 }; static const int trial_bufs[] = { 16384, 8192, 4096, 3584, 3072, 2560, 2048, 1536, -- 2.30.2