Re: Trying to minimize the impact of checkpoints

On 6/12/2004 1:44 PM, Jack Orenstein wrote:

> Jan Wieck wrote:
>> On 6/11/2004 2:02 PM, jao(at)geophile(dot)com wrote:
>>
>>> Quoting jao(at)geophile(dot)com:
>>>
>>>> When a checkpoint occurs, all operations slow way, way down.
>>>> The attached spreadsheet (xls file, prepared in OO so unlikely
>>>> to be dangerous) shows a run of a few hours, and the various spikes
>>>> every 25-30 minutes seem consistent with checkpointing. The
>>>> application is doing 1/2 reads and 1/2 inserts during this time.
>>>
>>>
>>> Sorry for being cryptic in my message. The spreadsheet contains
>>> iostat output.
>>
>>
>> Did you try to play with the background writer config options (new in
>> 7.5) at all?
>
> No, not yet. It looks like 7.5 won't be available in time for us to
> use in the first release of our product, so I've been very focused
> on how to best use 7.3-4.
>
> Any opinions on the stability of 7.5 and the effectiveness of the background
> writer in reducing variability in performance due to checkpoints?

I didn't save any of the charts done with 7.4, but the responsetime
spikes on checkpoints went up to 60 seconds without the bgwriter. If you
look at the last chart on this page

http://developer.postgresql.org/~wieck/vacuum_cost/

there are no spikes at all.

Jan

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