On May 8, 2007, at 2:59 AM, david@xxxxxxx wrote:
one issue with journaling filesystems, if you journal the data as well as the metadata you end up with a very reliable setup, however it means that all your data needs to be written twice, oncce to the journal, and once to the final location. the write to the journal can be slightly faster then a normal write to the final location (the journal is a sequential write to an existing file), however the need to write twice can effectivly cut your disk I/O bandwidth in half when doing heavy writes. worse, when you end up writing mor ethen will fit in the journal (128M is the max for ext3) the entire system then needs to stall while the journal gets cleared to make space for the additional writes.
That's why you want to mount ext3 partitions used with PostgreSQL with data=writeback.
Some folks will also use a small filesystem for pg_xlog and mount that as ext2.
-- Jim Nasby jim@xxxxxxxxx EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
