> Where are we on this issue? I've been able to replicate it pretty easily with PostgreSQL and continue to look into it. I've contacted Theodore Ts'o and have gotten some useful information, however I'm unable to replicate the behavior with the test program (even one that's been modified). What I've learned is:
- XLogWrite appears to take approx. 2.5 times longer when writing to a file allocated with posix_fallocate, but only the first time the file contents are overwritten. This is partially explained by how ext4 handles extents and uninitialized data, but 2.5x is MUCH more expensive than anticipated or expected here. - Writing zeroes to a file allocated with posix_fallocate (essentially adding a posix_fallocate step before the usual write-zeroes-in-a-loop approach) not only doesn't seem to hurt performance, it seems to help or at least have parity, *and* the space is guaranteed to exist on disk. At the very least that seems useful. -- Jon -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
