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Commit810a8b1

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Give up on running with NetBSD/OpenBSD's default semaphore settings.
This reverts commit38da053, whichattempted to preserve our ability to start with only 60 semaphores.Subsequent changes (particularly55b454d) have put that idea prettymuch permanently out of reach: people wishing to use Postgres v18 onOpenBSD or NetBSD will have no choice but to increase those platforms'default values of SEMMNI and SEMMNS.Hence, revert38da053's changes in SEMAS_PER_SET and the minimumtested value of max_connections. Adjust a comment from the subsequentpatch6d01541, and tweak the wording in runtime.sgml to make itclear that changing SEMMNI/SEMMNS is no longer even a little bitoptional on these platforms.Although38da053 was later back-patched into v17, leave that branchalone: it's still capable of starting with 60 semaphores, and there'sno reason to break that.Author: Tom Lane <tgl@sss.pgh.pa.us>Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>Discussion:https://postgr.es/m/E1tuZNv-0037Gs-34@gemulon.postgresql.orgDiscussion:https://postgr.es/m/1052019.1745947915@sss.pgh.pa.us
1 parente974f1c commit810a8b1

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3 files changed

+17
-24
lines changed

3 files changed

+17
-24
lines changed

‎doc/src/sgml/runtime.sgml

Lines changed: 12 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -782,19 +782,19 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
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<row>
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<entry><varname>SEMMNI</varname></entry>
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<entry>Maximum number of semaphore identifiers (i.e., sets)</entry>
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<entry>at least <literal>ceil(num_os_semaphores /19)</literal> plus room for other applications</entry>
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<entry>at least <literal>ceil(num_os_semaphores /16)</literal> plus room for other applications</entry>
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</row>
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<row>
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<entry><varname>SEMMNS</varname></entry>
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<entry>Maximum number of semaphores system-wide</entry>
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<entry><literal>ceil(num_os_semaphores /19) *20</literal> plus room for other applications</entry>
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<entry><literal>ceil(num_os_semaphores /16) *17</literal> plus room for other applications</entry>
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</row>
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<row>
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<entry><varname>SEMMSL</varname></entry>
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<entry>Maximum number of semaphores per set</entry>
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<entry>at least20</entry>
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<entry>at least17</entry>
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</row>
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<row>
@@ -841,7 +841,7 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
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(<xref linkend="guc-max-connections"/>), allowed autovacuum worker process
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(<xref linkend="guc-autovacuum-worker-slots"/>), allowed WAL sender process
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(<xref linkend="guc-max-wal-senders"/>), allowed background
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process (<xref linkend="guc-max-worker-processes"/>), etc., in sets of19.
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process (<xref linkend="guc-max-worker-processes"/>), etc., in sets of16.
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The runtime-computed parameter <xref linkend="guc-num-os-semaphores"/>
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reports the number of semaphores required. This parameter can be viewed
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before starting the server with a <command>postgres</command> command like:
@@ -851,17 +851,17 @@ $ <userinput>postgres -D $PGDATA -C num_os_semaphores</userinput>
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</para>
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<para>
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Each set of19 semaphores will
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also contain a20th semaphore which contains a <quote>magic
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Each set of16 semaphores will
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also contain a17th semaphore which contains a <quote>magic
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number</quote>, to detect collision with semaphore sets used by
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other applications. The maximum number of semaphores in the system
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is set by <varname>SEMMNS</varname>, which consequently must be at least
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as high as <literal>num_os_semaphores</literal> plus one extra for
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each set of19 required semaphores (see the formula in <xref
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each set of16 required semaphores (see the formula in <xref
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linkend="sysvipc-parameters"/>). The parameter <varname>SEMMNI</varname>
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determines the limit on the number of semaphore sets that can
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exist on the system at one time. Hence this parameter must be at
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least <literal>ceil(num_os_semaphores /19)</literal>.
864+
least <literal>ceil(num_os_semaphores /16)</literal>.
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Lowering the number
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of allowed connections is a temporary workaround for failures,
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which are usually confusingly worded <quote>No space
@@ -953,10 +953,10 @@ $ <userinput>postgres -D $PGDATA -C num_os_semaphores</userinput>
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<para>
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The default shared memory settings are usually good enough, unless
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you have set <literal>shared_memory_type</literal> to <literal>sysv</literal>.
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Youwillusually want to increase <literal>kern.ipc.semmni</literal>
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However, youwillneed to increase <literal>kern.ipc.semmni</literal>
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and <literal>kern.ipc.semmns</literal>,
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as <systemitem class="osname">NetBSD</systemitem>'s default settings
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for these areuncomfortably small.
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for these areunworkably small.
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</para>
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<para>
@@ -987,11 +987,11 @@ $ <userinput>postgres -D $PGDATA -C num_os_semaphores</userinput>
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<para>
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The default shared memory settings are usually good enough, unless
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you have set <literal>shared_memory_type</literal> to <literal>sysv</literal>.
990-
Youwillusually want to
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However, youwillneed to
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increase <literal>kern.seminfo.semmni</literal>
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and <literal>kern.seminfo.semmns</literal>,
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as <systemitem class="osname">OpenBSD</systemitem>'s default settings
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for these areuncomfortably small.
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for these areunworkably small.
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</para>
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<para>

‎src/backend/port/sysv_sema.c

Lines changed: 1 addition & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -50,14 +50,8 @@ typedef int IpcSemaphoreId;/* semaphore ID returned by semget(2) */
5050
* we allocate. It must be *less than* your kernel's SEMMSL (max semaphores
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* per set) parameter, which is often around 25. (Less than, because we
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* allocate one extra sema in each set for identification purposes.)
53-
*
54-
* The present value of 19 is chosen with one eye on NetBSD/OpenBSD's default
55-
* SEMMNS setting of 60. Remembering the extra sema per set, this lets us
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* allocate three sets with 57 useful semaphores before exceeding that, which
57-
* is enough to run our core regression tests. Users of those systems will
58-
* still want to raise SEMMNS for any sort of production work, though.
5953
*/
60-
#defineSEMAS_PER_SET19
54+
#defineSEMAS_PER_SET16
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6256
#defineIPCProtection(0600)/* access/modify by user only */
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‎src/bin/initdb/initdb.c

Lines changed: 4 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1128,15 +1128,14 @@ test_config_settings(void)
11281128
* for a given max_connections value. Note that it has been carefully
11291129
* crafted to provide specific values for the associated values in
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* trial_conns. We want it to return autovacuum_worker_slots's initial
1131-
* default value (16) for the maximum value in trial_conns (100), and we
1132-
* want it to return close to the minimum value we'd consider (3, which is
1133-
* the default of autovacuum_max_workers) for the minimum value in
1134-
* trial_conns (25).
1131+
* default value (16) for the maximum value in trial_conns[] (100), while
1132+
* it mustn't return less than the default value of autovacuum_max_workers
1133+
* (3) for the minimum value in trial_conns[].
11351134
*/
11361135
#defineAV_SLOTS_FOR_CONNS(nconns)((nconns) / 6)
11371136

11381137
staticconstinttrial_conns[]= {
1139-
100,50,40,30,25
1138+
100,50,40,30,20
11401139
};
11411140
staticconstinttrial_bufs[]= {
11421141
16384,8192,4096,3584,3072,2560,2048,1536,

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