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From: Jim Nasby <Jim.Nasby@BlueTreble.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
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: Mon, 23 Jan 2017 08:16:49 -0600
Message-ID: <6519b7ad-0aa6-c9f4-8869-20691107fb69@BlueTreble.com> (raw)
In-Reply-To: <26168.1485126221@sss.pgh.pa.us>
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	<ecd7ba88-0484-54be-5b8a-c48848438aea@BlueTreble.com>
	<19334.1485053684@sss.pgh.pa.us>
	<276bcca0-9bfd-e60f-243d-baf081b41946@BlueTreble.com>
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On 1/22/17 5:03 PM, Tom Lane wrote:
>> 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.

Currently they wouldn't, but there's concerns about the performance of 
some of the other ideas in this thread. Getting rid of negative entries 
that don't really help could reduce some of those concerns. Or perhaps 
the original complaint about STATRELATTINH could be solved by just 
disabling negative entries on that cache.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
855-TREBLE2 (855-873-2532)


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