Nailed the stats problem?

I think I (we) may have finally nailed the stats issue. The symptoms were the stats collector stopping to process data under load (this is different from the old stats-collector crashes under load that we had back in early 8.0). Since the latest changes regarding autovacuum made the probability for it happening around 100%25 when running the parallel regression tests, debugging was suddenly a lot easier.

Turns out there was a big problem in the pgwin32_select() emulation code (src/backend/port/win32/socket.c for the interested), that simply had it stop telling the caller that there was data available on the socket when it was under high load. And it only happens for UDP sockets (stats collector uses UDP because it's designed to drop packets under really heavy load in order not to slow down the actual database work).

pgwin32_select() still isn't fixed, but with the current architecture for the collector it's not needed anymore. Originally, when we had both a collector and a bufferer, the same code had to look at two sockets and needed it. Now it doesn't need to look at more than one socket, so we can use pgwin32_waitforsinglesocket(), which doesn't have this problem (that I've been able to tell, at least).

It's been applied to 8.2 and HEAD, and I'll hopefully have time to see if it is an easy backport to 8.1 sometime tomorrow. Per discussions on the list, we are not likely to backport it to 8.0 at all.

Hopefully, I'll be able to get rid of the hack that is pgwin32_select() altogether soon - with this change there is only one place left that uses it, and I'm going to look at replacing that with a proper native implementation as well.


I speak at and organize conferences around Open Source in general and PostgreSQL in particular.


Stockholm PUG 2016/5
Oct 25, 2016
Stockholm, Sweden
PGConf.EU 2016
Nov 1-4, 2016
Tallinn, Estonia
Berlin PUG
Nov 17, 2016
Berlin, Germany
PGConf.Asia 2016
Dec 2-3, 2016
Tokyo, Japan
FOSDEM + PGDay 2017
Feb 2-4, 2017
Brussels, Belgium


Postgres Vision 2016
Oct 11-13, 2016
San Francisco, USA
Postgres Open
Sep 13-16, 2016
Dallas, USA
Stockholm PUG 2016/4
Aug 31, 2016
Stockholm, Sweden
PG Day'16 Russia
Jul 6-8, 2016
St Petersburg, Russia
PGDay UK 2016
Jul 05, 2016
London, UK
More past conferences