Re: [HACKERS][PATCH] Applying PMDK to WAL operations for persistent memory

On Thu, Jan 25, 2018 at 8:32 PM, Tsunakawa, Takayuki
<tsunakawa.takay@jp.fujitsu.com> wrote:
> As I showed previously, regular file writes on PCIe flash, *not writes using PMDK on persistent memory*, was 20%
fasterwith open_datasync than with fdatasync.
 

If I understand correctly, those results are all just pg_test_fsync
results.  That's not reflective of what will happen when the database
is actually running.  When you use open_sync or open_datasync, you
force WAL write and WAL flush to happen simultaneously, instead of
letting the WAL flush be delayed.

> And you said open_datasync was significantly faster than fdatasync.  Could you show your results?  What device and
filesystemdid you use?
 

I don't have the results handy at the moment.  We found it to be
faster on a database benchmark where the WAL was stored on an NVRAM
device.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company