Re: Protect syscache from bloating with negative cache entries

From: David Steele <david(at)pgmasters(dot)net>
To: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: michael(dot)paquier(at)gmail(dot)com, Jim(dot)Nasby(at)bluetreble(dot)com, tgl(at)sss(dot)pgh(dot)pa(dot)us, robertmhaas(at)gmail(dot)com, craig(at)2ndquadrant(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Protect syscache from bloating with negative cache entries
Date: 2017-03-04 00:54:50
Message-ID: 6eb3b24b-c0eb-b8ca-f847-609704e2a370@pgmasters.net
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On 2/1/17 1:25 AM, Kyotaro HORIGUCHI wrote:
> Hello, thank you for moving this to the next CF.
>
> At Wed, 1 Feb 2017 13:09:51 +0900, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote in <CAB7nPqRFhUv+GX=eH1bo7xYHS79-gRj1ecu2QoQtHvX9RS=JYA(at)mail(dot)gmail(dot)com>
>> On Tue, Jan 24, 2017 at 4:58 PM, Kyotaro HORIGUCHI
>> <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> Six new syscaches in 665d1fa was conflicted and 3-way merge
>>> worked correctly. The new syscaches don't seem to be targets of
>>> this patch.
>>
>> To be honest, I am not completely sure what to think about this patch.
>> Moved to next CF as there is a new version, and no new reviews to make
>> the discussion perhaps move on.
>
> I'm thinking the following is the status of this topic.
>
> - The patch stll is not getting conflicted.
>
> - This is not a hollistic measure for memory leak but surely
> saves some existing cases.
>
> - Shared catcache is another discussion (and won't really
> proposed in a short time due to the issue on locking.)
>
> - As I mentioned, a patch that caps the number of negative
> entries is avaiable (in first-created - first-delete manner)
> but it is having a loose end of how to determine the
> limitation.

While preventing bloat in the syscache is a worthwhile goal, it appears
there are a number of loose ends here and a new patch has not been provided.

It's a pretty major change so I recommend moving this patch to the
2017-07 CF.

--
-David
david(at)pgmasters(dot)net

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