Re: Redesigning checkpoint_segments

On 02/05/2015 04:47 PM, Andres Freund wrote:
> On 2015-02-05 09:42:37 -0500, Robert Haas wrote:
>> I previously proposed 100 segments, or 1.6GB.  If that seems too
>> large, how about 64 segments, or 1.024GB?  I think there will be few
>> people who can't tolerate a gigabyte of xlog under peak load, and an
>> awful lot who will benefit from it.
>
> It'd be quite easier to go there if we'd shrink back to the min_size
> after a while, after having peaked above it. IIUC the patch doesn't do
> that?

It doesn't actively go and remove files once they've already been 
recycled, but if the system stays relatively idle for several 
checkpoints, the WAL usage will shrink down again. That's the core idea 
of the patch.

If the system stays completely or almost completely idle, that won't 
happen though, because then it will never switch to a new segment so 
none of the segments become old so that they could be removed.

- Heikki