From: | Josh Berkus <josh(at)agliodbs(dot)com> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers |
Date: | 2013-09-05 22:11:53 |
Message-ID: | 522901A9.1070902@agliodbs.com |
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Lists: | pgsql-hackers |
On 09/05/2013 02:16 PM, Bruce Momjian wrote:
>> Well, the real problem with this patch is that it documents what the
>> auto-tuning algorithm is; without that commitment, just saying "-1 means
>> autotune" might be fine.
>
> OK, but I did this based on wal_buffers, which has a -1 default, calls
> it auto-tuning, and explains how the default is computed.
I don't see a real problem with this. For users who have set their
shared_buffers correctly, effective_cache_size should also be correct.
> The problem there is that many users are told to tune shared_buffers,
> but don't touch effective cache size. Having initdb set the
> effective_cache_size value would not help there. Again, this is all
> based on the auto-tuning of wal_buffers.
Standard advice we've given in the past is 25% shared buffers, 75%
effective_cache_size. Which would make EFS *3X* shared_buffers, not 4X.
Maybe we're changing the conventional calculation, but I thought I'd
point that out.
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
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