Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers

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