From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
---|---|
To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Redesigning checkpoint_segments |
Date: | 2013-06-06 20:09:39 |
Message-ID: | 51B0EC83.60700@vmware.com |
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Lists: | pgsql-hackers |
On 06.06.2013 20:24, Josh Berkus wrote:
>> Yeah, something like that :-). I was thinking of letting the estimate
>> decrease like a moving average, but react to any increases immediately.
>> Same thing we do in bgwriter to track buffer allocations:
>
> Seems reasonable.
Here's a patch implementing that. Docs not updated yet. I did not change
the way checkpoint_segments triggers checkpoints - that'll can be a
separate patch. This only decouples the segment preallocation behavior
from checkpoint_segments. With the patch, you can set
checkpoint_segments really high, without consuming that much disk space
all the time.
> Given the behavior of xlog, I'd want to adjust the
> algo so that peak usage on a 24-hour basis would affect current
> preallocation. That is, if a site regularly has a peak from 2-3pm where
> they're using 180 segments/cycle, then they should still be somewhat
> higher at 2am than a database which doesn't have that peak. I'm pretty
> sure that the bgwriter's moving average cycles much shorter time scales
> than that.
Makes sense. I didn't implement that in the attached, though.
Having a separate option to specify a minimum number of segments (or
rather minimum size in MB) to keep preallocated would at least allow a
DBA to set that manually, based on the observed peak. I didn't implement
such a manual option in the attached, but that would be easy.
- Heikki
Attachment | Content-Type | Size |
---|---|---|
dynamic-xlogfileslop-1.patch | text/x-diff | 12.8 KB |
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