Date: Fri, 17 May 2024 14:21:23 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: "Imseih (AWS), Sami" <simseih@amazon.com>,
	Justin Pryzby <pryzby@telsasoft.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: problems with "Shared Memory and Semaphores" section of docs
Message-ID: <20240517192123.GA1933425@nathanxps13>
References: <20240517164452.GA1914161@nathanxps13>
 <2463906.1715965795@sss.pgh.pa.us>
 <20240517174837.GB1918496@nathanxps13>
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On Fri, May 17, 2024 at 12:48:37PM -0500, Nathan Bossart wrote:
> On Fri, May 17, 2024 at 01:09:55PM -0400, Tom Lane wrote:
>> Nathan Bossart <nathandbossart@gmail.com> writes:
>>> At a bare minimum, we should probably fix the obvious problems, but I
>>> wonder if we could simplify this section a bit, too.
>> 
>> Yup.  "The definition of insanity is doing the same thing over and
>> over and expecting different results."  Time to give up on documenting
>> these things in such detail.  Anybody who really wants to know can
>> look at the source code.
> 
> Cool.  I'll at least fix the back-branches as-is, but I'll see about
> revamping this stuff for v18.

Attached is probably the absolute least we should do for the back-branches.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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From 853104fa59bb1c219f02f71ece0d5106cb6c0588 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Fri, 17 May 2024 14:17:59 -0500
Subject: [PATCH v1 1/1] fix kernel resources docs on back-branches

---
 doc/src/sgml/runtime.sgml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 6047b8171d..883a849e6f 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
        <row>
         <entry><varname>SEMMNI</varname></entry>
         <entry>Maximum number of semaphore identifiers (i.e., sets)</entry>
-        <entry>at least <literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 5) / 16)</literal> plus room for other applications</entry>
+        <entry>at least <literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 7) / 16)</literal> plus room for other applications</entry>
        </row>
 
        <row>
         <entry><varname>SEMMNS</varname></entry>
         <entry>Maximum number of semaphores system-wide</entry>
-        <entry><literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 5) / 16) * 17</literal> plus room for other applications</entry>
+        <entry><literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 7) / 16) * 17</literal> plus room for other applications</entry>
        </row>
 
        <row>
@@ -838,7 +838,8 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
     When using System V semaphores,
     <productname>PostgreSQL</productname> uses one semaphore per allowed connection
     (<xref linkend="guc-max-connections"/>), allowed autovacuum worker process
-    (<xref linkend="guc-autovacuum-max-workers"/>) and allowed background
+    (<xref linkend="guc-autovacuum-max-workers"/>), allowed WAL sender process
+    (<xref linkend="guc-max-wal-senders"/>), and allowed background
     process (<xref linkend="guc-max-worker-processes"/>), in sets of 16.
     Each such set will
     also contain a 17th semaphore which contains a <quote>magic
@@ -852,7 +853,7 @@ psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such
     linkend="sysvipc-parameters"/>).  The parameter <varname>SEMMNI</varname>
     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 <literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 5) / 16)</literal>.
+    least <literal>ceil((max_connections + autovacuum_max_workers + max_wal_senders + max_worker_processes + 7) / 16)</literal>.
     Lowering the number
     of allowed connections is a temporary workaround for failures,
     which are usually confusingly worded <quote>No space
-- 
2.25.1


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