Jon Nelson <jnelson+pg...@jamponi.net> writes: > At this point I'm convinced that the issue is a pathological case in > ext4. The performance impact disappears as soon as the unwritten > extent(s) are written to with real data. Thus, even though allocating > files with posix_fallocate is - frequently - orders of magnitude > quicker than doing it with write(2), the subsequent re-write can be > more expensive. At least, that's what I'm gathering from the various > threads. Why this issue didn't crop up in earlier testing and why I > can't seem to make test_fallocate do it (even when I modify > test_fallocate to write to the newly-allocated file in a mostly-random > fashion) has me baffled.
Does your test program use all the same writing options that the real WAL writes do (like O_DIRECT)? > Should this feature be reconsidered? Well, ext4 isn't the whole world, but it's sure a big part of it. The real point though is that obviously we didn't do enough performance testing, so we'd better do more before deciding what to do. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers