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 PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
pgstat-coalesce-v3.patch
Description: binary/octet-stream
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