Re: Expose checkpoint start/finish times into SQL.

On Apr 3, 2008, at 7:08 PM, Andrew Dunstan wrote:

>
>
> Joshua D. Drake wrote:
>>> Theo Schlossnagle wrote:
>>>
>>>> First whack at exposing the start and finish checkpoint times into
>>>> SQL.
>>>>
>>> Why is that useful?
>>>
>>
>> For knowing how long checkpoints are taking. If they are taking too
>> long you may need to adjust your bgwriter settings, and it is a
>> serious drag to parse postgresql logs for this info.
>>
>>
>>
>
> Even if this were true, surely the answer is to improve the logging.
>
> Has this feature been discussed on -hackers? I don't recall it (and
> my memory has plenty of holes in it), but I'm sure that after
> attending my talk last Sunday Theo hasn't sent in a patch for an
> undiscussed feature ;-)


Andrew: I don't think this feature has been discussed on hackers.  The
patch took about 15 minutes to author, so it sounds like the most
concise way to start a conversation.  Seems silly to start the
conversation on hackers with a patch. :-)

Alvaro: Thanks, I flip that to GetCurrentTimestamp()

Heikki: It it useful for knowing when the last checkpoint occurred.
Like Robert, we have situations where reading the log file is a PITA
-- so this provides that information.  I originally planned on only
adding the start time, but figured adding the end would make sense too.

Tom: It worked for me in my testing, though I did not extensively
tested.  I didn't see anywhere the stats are zero'd out, so I believe
the timestamp is zero at start and then only ever set to the starttime
during a checkpoint invocation.  I admittedly don't have a thorough
understanding of that code -- but that segment (before my patch)
looked pretty concise.

--
Theo Schlossnagle
Esoteric Curio -- http://lethargy.org/
OmniTI Computer Consulting, Inc. -- http://omniti.com/