On Wed, Jan 24, 2018 at 10:31 PM, Tsunakawa, Takayuki
<tsunakawa.takay@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
concernthat users might hit performance degredation if they are using PostgreSQL on older systems. But it's also
mottainaithat 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
