I think the conclusion from the discussion is that O_DIRECT is in addition to the sync method, rather than in place of it, because O_DIRECT doesn't have the same media write guarantees as fsync(). Would you update the patch to do O_DIRECT in addition to O_SYNC or fsync() and see if there is a performance win?
Thanks. --------------------------------------------------------------------------- ITAGAKI Takahiro wrote: > Neil Conway <[EMAIL PROTECTED]> wrote: > > > > The patch adds a new choice "open_direct" to wal_sync_method. > > Have you looked at what the performance difference of this option is? > > Yes, I've tested pgbench and dbt2 and their performances have improved. > The two results are as follows: > > 1. pgbench -s 100 on one Pentium4, 1GB mem, 2 ATA disks, Linux 2.6.8 > (attached image) > tps | wal_sync_method > -------+------------------------------------------------------- > 147.0 | open_direct + write multipage (previous patch) > 147.2 | open_direct (this patch) > 109.9 | open_sync > > 2. dbt2 100WH on two opterons, 8GB mem, 12 SATA-RAID disks, Linux 2.4.20 > tpm | wal_sync_method > --------+------------------------------------------------------ > 1183.9 | open_direct (this patch) > 911.3 | fsync > > > > > http://www.mail-archive.com/pgsql-patches@postgresql.org/msg07186.html > > Is this data still applicable to the revised patch? > > Direct-IO might be good on some machines, and bad on others. > This data is another reason that I revised the patch; > If you don't use open_direct, WAL writer behaves quite similarly to former. > > However, the performances did not go down at least on my benchmarks. > I have no idea why the above data was bad... > > --- > ITAGAKI Takahiro > NTT Cyber Space Laboratories > [ Attachment, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED] -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings