Re: [HACKERS] Performance while loading data and indexing

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:

> Can anyone clarify if "data=writeback" is safe for PostgreSQL.
> Specifically, are the data files recovered properly or is this option
> only for a filesystem containing WAL?

"data=writeback" means that no data is journaled, just metadata (which
is like XFS or Reiser). An fsync() call should still do what it
normally does, commit the writes to disk before returning.

"data=journal" journals all data and is the slowest and safest.
"data=ordered" writes out data blocks before committing a journal
transaction, which is faster than full data journaling (since data
doesn't get written twice) and almost as safe. "data=writeback" is
noted to keep obsolete data in the case of some crashes (since the
data may not have been written yet) but a completed fsync() should
ensure that the data is valid.

So I guess I'd probably use data=ordered for an all-on-one-fs
installation, and data=writeback for a WAL-only drive.

Hope this helps...

-Doug