On 30 November 2017 at 11:30, Petr Jelinek <petr.jeli...@2ndquadrant.com> wrote: > On 30/11/17 00:47, Andres Freund wrote: >> On 2017-11-30 00:45:44 +0100, Petr Jelinek wrote: >>> I don't understand. I mean sure the SnapBuildWaitSnapshot() can live >>> with it, but the problematic logic happens inside the >>> XactLockTableInsert() and SnapBuildWaitSnapshot() has no way of >>> detecting the situation short of reimplementing the >>> XactLockTableInsert() instead of calling it. >> >> Right. But we fairly trivially can change that. I'm remarking on it >> because other people's, not yours, suggestions aimed at making this >> bulletproof. I just wanted to make clear that I don't think that's >> necessary at all. >> > > Okay, then I guess we are in agreement. I can confirm that the attached > fixes the issue in my tests. Using SubTransGetTopmostTransaction() > instead of SubTransGetParent() means 3 more ifs in terms of extra CPU > cost for other callers. I don't think it's worth worrying about given we > are waiting for heavyweight lock, but if we did we can just inline the > code directly into SnapBuildWaitSnapshot().
This will still fail an Assert in TransactionIdIsInProgress() when snapshots are overflowed. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
