> Once I got above messages, write performance is dramatically > degraded, even though I didn't take detailed investigation.
> I could reproduce it on the latest master branch without my > enhancement, so I guess it is not a problem something special > to me. > One other strangeness is, right now, this problem is only > happen on my virtual machine environment - VMware ESXi 5.5.0. > I couldn't reproduce the problem on my physical environment > (Fedora20, core i5-4570S).
We've seen sporadic reports of that sort of behavior for years, but no developer has ever been able to reproduce it reliably. Now that you've got a reproducible case, do you want to poke into it and see what's going on?
I didn't know we were trying to reproduce it, nor that it was a mystery. Do anything that causes serious IO constipation, and you will probably see that message. For example, turn off synchronous_commit and run the default pgbench transaction at a large scale but that still comfortably fits in RAM, and wait for a checkpoint sync phase to kick in.
The pgstat wait timeout is a symptom, not the cause.