On 8 June 2012 05:01, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Peter Geoghegan <peter@2ndquadrant.com> writes:
>> On 7 June 2012 18:03, Robert Haas <robertmhaas@gmail.com> wrote:
>>> On Thu, Jun 7, 2012 at 12:52 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>>>> Clearly, delaying checkpoint indefinitely would be a high risk choice.
>>>> But they won't be delayed indefinitely, since changes cause WAL
>>>> records to be written and that would soon cause another checkpoint.
>
>>> But that's exactly the problem - it might not be soon at all.
>
>> Your customer's use-case seems very narrow, and your complaint seems
>> unusual to me, but couldn't you just get the customer to force
>> checkpoints in a cronjob or something? CheckPointStmt will force,
>> provided !RecoveryInProgress() .
>
> I think both you and Simon have completely missed the point. This
> is not a "use case" in the sense of someone doing it deliberately.
> This is about data redundancy, ie, if you lose your WAL through some
> unfortunate mishap, are you totally screwed or is there a reasonable
> chance that the data is on-disk in the main data store? I would guess
> that the incidents Robert has been talking about were cases where EDB
> were engaged to do crash recovery, and were successful precisely because
> PG wasn't wholly dependent on the WAL copy of the data.
Apart from the likely point that hint bits exist on disk...
> This project has always put reliability first. It's not clear to me why
> we would compromise that across-the-board in order to slightly reduce
> idle load in replication configurations. Yeah, it's probably not a
> *large* compromise ... but it is a compromise, and one that doesn't
> seem to me to be very well-advised. We can fix the idle-load issue
> without compromising on this basic goal; it will just take more than
> a ten-line patch to do it.
So now the standard for my patches is that I must consider what will
happen if the xlog is deleted?
Tell me such a rule is applied uniformly to all patches then I would be happy.
I will revoke, not because of the sense in this argument but because
you personally ask for it.
--
Simon Riggs http://www.2ndQuadrant.com/
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