On Wed, Jan 24, 2018 at 10:31 PM, Tsunakawa, Takayuki <tsunakawa.ta...@jp.fujitsu.com> wrote: >> This is just a guess, of course. You didn't mention what the underlying >> storage for your test was? > > Uh, your guess was correct. My file system was ext3, where fsync() writes > all dirty buffers in page cache.
Oh, ext3 is terrible. I don't think you can do any meaningful benchmark results on ext3. Use ext4 or, if you prefer, xfs. > As you said, open_datasync was 20% faster than fdatasync on RHEL7.2, on a LVM > volume with ext4 (mounted with options noatime, nobarrier) on a PCIe flash > memory. So does that mean it was faster than your PMDK implementation? > What do you think about changing the default value of wal_sync_method on > Linux in PG 11? I can understand the concern that users might hit > performance degredation if they are using PostgreSQL on older systems. But > it's also mottainai that many users don't notice the benefits of > wal_sync_method = open_datasync on new systems. Well, some day persistent memory may be a common enough storage technology that such a change makes sense, but these days most people have either SSD or spinning disks, where the change would probably be a net negative. It seems more like something we might think about changing in PG 20 or PG 30. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
