Re: Re: PATCH: Split stats file per database WAS: autovacuum stress-testing our system

Hi,

On 03/15/2016 03:04 AM, Noah Misch wrote:
> On Mon, Mar 14, 2016 at 01:33:08PM +0100, Tomas Vondra wrote:
>> On 03/14/2016 07:14 AM, Noah Misch wrote:
>>> On Mon, Mar 14, 2016 at 02:00:03AM +0100, Tomas Vondra wrote:
>>>> +     * XXX Maybe this should also care about the clock skew, just like the
>>>> +     *     block a few lines down.
>>>
>>> Yes, it should.  (The problem is large (>~100s), backward clock resets, not
>>> skew.)  A clock reset causing "msg->clock_time < dbentry->stats_timestamp"
>>> will usually also cause "msg->cutoff_time < dbentry->stats_timestamp".  Such
>>> cases need the correction a few lines down.
>>
>> I'll look into that. I have to admit I have a hard time reasoning about the
>> code handling clock skew, so it might take some time, though.
>
> No hurry; it would be no problem to delay this several months.

Attached is a patch that should fix the coalescing, including the clock
skew detection. In the end I reorganized the code a bit, moving the
check at the end, after the clock skew detection. Otherwise I'd have to
do the clock skew detection on multiple places, and that seemed ugly.

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
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