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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: robertmhaas@gmail.com
Cc: craig@2ndquadrant.com
Cc: pgsql-hackers@postgresql.org
Subject: Re: Protect syscache from bloating with negative cache entries
Date: Sun, 22 Jan 2017 18:03:41 -0500
Message-ID: <26168.1485126221@sss.pgh.pa.us> (raw)
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Jim Nasby <Jim.Nasby@bluetreble.com> writes:
>> Ahh, I hadn't considered that. So one idea would be to only track
>> negative entries on caches where we know they're actually useful. That
>> might make the performance hit of some of the other ideas more
>> tolerable. Presumably you're much less likely to pollute the namespace
>> cache than some of the others.

> Ok, after reading the code I see I only partly understood what you were 
> saying. In any case, it might still be useful to do some testing with 
> CATCACHE_STATS defined to see if there's caches that don't accumulate a 
> lot of negative entries.

There definitely are, according to my testing, but by the same token
it's not clear that a shutoff check would save anything.

			regards, tom lane


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