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max_connections, solaris semaphores and initdb

From: Isaac Vetter <ivetter(at)math(dot)purdue(dot)edu>
To: pgsql-novice(at)postgresql(dot)org
Subject: max_connections, solaris semaphores and initdb
Date: 2008-01-11 17:08:27
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
Hi pgsql experts;

I've been a little surprised at the high knowledge level of the 
"novices" on this list, so if this isn't a novice question, let me know 
and I'll send it to the regular list.

I'm running postgresql 7.4 on Solaris 9 and want to increase the value 
of postgresql.conf's max_connections for an existing, running install. 
I've edited /etc/system to what I think are more appropriate, but 
definitely higher, values. Then I changed the value of max_connections 
to 768; however, by watching the pg_stat_activity view and the 
serverlog, connections are rejected when the number of connections 
approaches 200 (with the infamous: "FATAL:  connection limit exceeded 
for non-superusers" error).

I ran across a mention of initdb determining the greatest possible 
number of connections according to kernerl settings. So presumably, when 
postgresql is first setup, the highest value of max_connections is 
decided then.

A couple questions:
0) Is this correct? Does initdb set an unchaged value that quietly 
limits the high end of max_connections?

1) Is there a way to get postgresql to reset this value that determines 
the maximum value of max_connections, without dumping, re-running initdb 
and loading? Is there a way to see what this value is?

2) Are there any easy postgresql load testing tools? I ran across Tsung, 
  but haven't had time to compile erlang. What do others do for load 


Isaac Vetter

I had trouble finding recent example Solaris /etc/system numbers, so 
I've included mine below. I'm still testing these are am not a solaris 
sysadmin - ymmv.

* On an 8 gig sun4u running solaris 9
set shmsys:shminfo_shmmax=4294967295
set shmsys:shminfo_shmmin=1
set shmsys:shminfo_shmmni=512
set shmsys:shminfo_shmseg=512
*max # of semaphores
set semsys:seminfo_semmns=2048
*max # of semaphore sets
set semsys:seminfo_semmni=1024
*max # of semaphores per set
set semsys:seminfo_semmsl=128


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Next:From: Tom LaneDate: 2008-01-11 18:55:51
Subject: Re: max_connections, solaris semaphores and initdb
Previous:From: johnfDate: 2008-01-11 16:30:05
Subject: Re: Connecting to the database server

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