On Thu, Aug 15, 2013 at 12:08:57PM -0500, Jon Nelson wrote: > > 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.
Is it time to revert this patch until we know more? -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
