On Sat, Apr 26, 2014 at 9:16 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Peter Geoghegan <p...@heroku.com> writes: >> Backend fsyncs are theoretically still possible after the fsync >> request queue compaction patch (which was subsequently back-patched to >> all supported release branches). However, I'm reasonably confident >> that that patch was so effective as to make a backend fsync all but >> impossible. > > What's your evidence for that claim?
I don't have any evidence, but I think it unlikely that this is an occurrence that is seen in the real world. I was not able to see any instances of it on the entire Heroku fleet at one point a few months back, for one thing. For another, I have never observed this with any benchmark, even though pgbench-tools presents buffers_backend_fsync for each test run. The queue compaction patch completely fixed Greg Smith's original test case. Even then, I believe it was considered more of a patch addressing an edge case than anything else. Even the comments above ForwardFsyncRequest() consider the occurance of backend fsyncs to be only "theoretically possible". If anyone is aware of any cases where this is still actually known to happen in production, I'd like to hear about them. However, ISTM that if this actually does still happen, those cases would be better served by surfacing the problem in the logs. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers