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Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org, Greg Smith <greg(at)2ndquadrant(dot)com>
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
Date: 2010-11-17 01:22:08
Message-ID: 11497.1289956928@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> Well, we're not going to increase the default to gigabytes, but we could
>> very probably increase it by a factor of 10 or so without anyone
>> squawking.  It's been awhile since I heard of anyone trying to run PG in
>> 4MB shmmax.  How much would a change of that size help?

> Last I checked, though, this comes out of the allocation available to
> shared_buffers.  And there definitely are several OSes (several linuxes,
> OSX) still limited to 32MB by default.

Sure, but the current default is a measly 64kB.  We could increase that
10x for a relatively small percentage hit in the size of shared_buffers,
if you suppose that there's 32MB available.  The current default is set
to still work if you've got only a couple of MB in SHMMAX.

What we'd want is for initdb to adjust the setting as part of its
probing to see what SHMMAX is set to.

			regards, tom lane

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Next:From: Robert HaasDate: 2010-11-17 03:07:49
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?
Previous:From: Tom LaneDate: 2010-11-17 01:17:43
Subject: Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?

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