Hello, I found that the formulas to calculate SEMMNI and SEMMNS
are incorrect in 9.2 and later.
http://www.postgresql.org/docs/9.5/static/kernel-resources.html
All of them say that the same thing as following,
| SEMMNI Maximum number of semaphore identifiers (i.e., sets)
|
| at least ceil((max_connections + autovacuum_max_workers + 4) / 16)
|
| SEMMNS Maximum number of semaphores system-wide
|
| ceil((max_connections + autovacuum_max_workers + 4) / 16) * 17
| plus room for other applications
But actually the number of semaphores PostgreSQL needs is
calculated as following in 9.4 and later.
numSemas = MaxConnections + NUM_AUXILIARY_PROCS(=4)
MaxConnections = max_connections + autovacuum_max_workers + 1 +
max_worker_processes
So, the formula for SEMMNI should be
ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16)
and SEMMNS should have the same fix.
In 9.3 and 9.2, the documentation says the same thing but
actually it is calculated as following,
numSemas = MaxConnections + NUM_AUXILIARY_PROCS(=4)
MaxConnections = max_connections + autovacuum_max_workers + 1 +
GetNumShmemAttachedBgworkers()
Omitting GetNumShmemAttachedBgworkers, the actual formula is
ceil((max_connections + autovacuum_max_workers + 5) / 16)
In 9.1, NUM_AUXILIARY_PROCS is 3 so the documentations is correct.
I attached two patches for 9.2-9.3 and 9.4-9.6dev
respectively. patch command complains a bit on applying it on
9.2.
On the platforforms that doesn't have tas operation needs
additional 1024 + 64 semaphores but I understand it as out of
scope of the documentation.
One concern is that 'at least' and 'plus room for other
applications' are mixed in the table 17-1, especially for SEMMNI
and SEMMNS. It seems to me that they should be in the same
wording, but it is not an actual problem.
regards,
--
Kyotaro Horiguchi
NTT Open Source Software Center
>From 6da5ad413dff4724fee75f1ba09013b6033f76ca Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyot...@lab.ntt.co.jp>
Date: Wed, 3 Feb 2016 11:35:43 +0900
Subject: [PATCH] Fix the formula to calculate SEMMNI and SEMMNS in
documentation
---
doc/src/sgml/runtime.sgml | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 0db3807..45579da 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -645,13 +645,13 @@ psql: could not connect to server: No such file or directory
<row>
<entry><varname>SEMMNI</></>
<entry>Maximum number of semaphore identifiers (i.e., sets)</>
- <entry>at least <literal>ceil((max_connections + autovacuum_max_workers + 4) / 16)</literal></>
+ <entry>at least <literal>ceil((max_connections + autovacuum_max_workers + 5) / 16)</literal></>
</row>
<row>
<entry><varname>SEMMNS</></>
<entry>Maximum number of semaphores system-wide</>
- <entry><literal>ceil((max_connections + autovacuum_max_workers + 4) / 16) * 17</literal> plus room for other applications</>
+ <entry><literal>ceil((max_connections + autovacuum_max_workers + 5) / 16) * 17</literal> plus room for other applications</>
</row>
<row>
--
1.8.3.1
>From aaf51a50e942edfa35af20a8a1d8b8719155664b Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyot...@lab.ntt.co.jp>
Date: Wed, 3 Feb 2016 11:19:58 +0900
Subject: [PATCH] Fix the formula to calculate SEMMNI and SEMMNS in
documentation
---
doc/src/sgml/runtime.sgml | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 650d455..4b2e403 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -645,13 +645,13 @@ psql: could not connect to server: No such file or directory
<row>
<entry><varname>SEMMNI</></>
<entry>Maximum number of semaphore identifiers (i.e., sets)</>
- <entry>at least <literal>ceil((max_connections + autovacuum_max_workers + 4) / 16)</literal></>
+ <entry>at least <literal>ceil((max_connections + autovacuum_max_workers max_worker_processes + 5) / 16)</literal></>
</row>
<row>
<entry><varname>SEMMNS</></>
<entry>Maximum number of semaphores system-wide</>
- <entry><literal>ceil((max_connections + autovacuum_max_workers + 4) / 16) * 17</literal> plus room for other applications</>
+ <entry><literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16) * 17</literal> plus room for other applications</>
</row>
<row>
--
1.8.3.1
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
