Re: often PREPARE can generate high load (and sometimes minutes long unavailability)

On Mon, Feb 24, 2014 at 7:02 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>wrote:

>
>
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> 2014-02-23 21:32 GMT+01:00 Andres Freund <andres(at)2ndquadrant(dot)com>:
>
> Hi,
>>
>> On 2014-02-23 20:04:39 +0100, Pavel Stehule wrote:
>> > There is relative few very long ProcArrayLocks lwlocks
>> >
>> > This issue is very pathologic on fast computers with more than 8 CPU.
>> This
>> > issue was detected after migration from 8.4 to 9.2. (but tested with
>> same
>> > result on 9.0) I see it on devel 9.4 today actualized.
>> >
>> > When I moved PREPARE from cycle, then described issues is gone. But
>> when I
>> > use a EXECUTE IMMEDIATELY, then the issue is back. So it looks it is
>> > related to planner, ...
>>
>> In addition to the issue Jeff mentioned, I'd suggest trying the same
>> workload with repeatable read. That can do *wonders* because of the
>> reduced number of snapshots.
>>
>>
> I tested it, and it doesn't help.
>
> Is there some patch, that I can test related to this issue?
>

This is the one that I was referring to:

http://www.postgresql.org/message-id/11927.1384199294@sss.pgh.pa.us

Cheers,

Jeff