From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jim Nasby <Jim.Nasby@bluetreble.com>
cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>,
 robertmhaas@gmail.com,
        craig@2ndquadrant.com, pgsql-hackers@postgresql.org
Subject: Re: Protect syscache from bloating with negative cache entries
In-reply-to: <683113d7-c7a7-1a0f-da7c-b197b08a6440@BlueTreble.com>
References: 
 <CA+TgmoaMPbN5vvH33zLK7MR+PiCYWPvTHmSSrDab4vurLOXS-Q@mail.gmail.com>
 <23492.1482264621@sss.pgh.pa.us>
 <20161221.102109.51106943.horiguchi.kyotaro@lab.ntt.co.jp>
 <20161226.173147.73783918.horiguchi.kyotaro@lab.ntt.co.jp>
 <ecd7ba88-0484-54be-5b8a-c48848438aea@BlueTreble.com>
 <19334.1485053684@sss.pgh.pa.us>
 <276bcca0-9bfd-e60f-243d-baf081b41946@BlueTreble.com>
 <683113d7-c7a7-1a0f-da7c-b197b08a6440@BlueTreble.com>
Comments: In-reply-to Jim Nasby <Jim.Nasby@bluetreble.com>
	message dated "Sun, 22 Jan 2017 16:51:53 -0600"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <26167.1485126221.1@sss.pgh.pa.us>
Date: Sun, 22 Jan 2017 18:03:41 -0500
Message-ID: <26168.1485126221@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

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


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers