-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Stef Telford wrote: > Mark Kirkwood wrote: >> Scott Carey wrote: >>> A little extra info here >> md, LVM, and some other tools do >>> not allow the file system to use write barriers properly.... So >>> those are on the bad list for data integrity with SAS or SATA >>> write caches without battery back-up. However, this is NOT an >>> issue on the postgres data partition. Data fsync still works >>> fine, its the file system journal that might have out-of-order >>> writes. For xlogs, write barriers are not important, only >>> fsync() not lying. >>> >>> As an additional note, ext4 uses checksums per block in the >>> journal, so it is resistant to out of order writes causing >>> trouble. The test compared to here was on ext4, and most >>> likely the speed increase is partly due to that. >>> >>> >> [Looks at Stef's config - 2x 7200 rpm SATA RAID 0] I'm still >> highly suspicious of such a system being capable of outperforming >> one with the same number of (effective) - much faster - disks >> *plus* a dedicated WAL disk pair... unless it is being a little >> loose about fsync! I'm happy to believe ext4 is better than ext3 >> - but not that much! > >> However, its great to have so many different results to compare >> against! > >> Cheers > >> Mark > > postgres@rob-desktop:~$ /usr/lib/postgresql/8.3/bin/pgbench -c 24 > -t 12000 test_db starting vacuum...end. transaction type: TPC-B > (sort of) scaling factor: 100 number of clients: 24 number of > transactions per client: 12000 number of transactions actually > processed: 288000/288000 tps = 3662.200088 (including connections > establishing) tps = 3664.823769 (excluding connections > establishing) > > > (Nb; Thread here; > http://www.ocztechnologyforum.com/forum/showthread.php?t=54038 ) Fyi, I got my intel x25-m in the mail, and I have been benching it for the past hour or so. Here are some of the rough and ready figures. Note that I don't get anywhere near the vertex benchmark. I did hotplug it and made the filesystem using Theodore Ts'o webpage directions ( http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/ ) ; The only thing is, ext3/4 seems to be fixated on a blocksize of 4k, I am wondering if this could be part of the 'problem'. Any ideas/thoughts on tuning gratefully received. Anyway, benchmarks (same system as previously, etc) (ext4dev, 4k block size, pg_xlog on 2x7.2krpm raid-0, rest on SSD) root@debian:~# /usr/lib/postgresql/8.3/bin/pgbench -c 24 -t 12000 test_db starting vacuum...end. transaction type: TPC-B (sort of) scaling factor: 100 number of clients: 24 number of transactions per client: 12000 number of transactions actually processed: 288000/288000 tps = 1407.254118 (including connections establishing) tps = 1407.645996 (excluding connections establishing) (ext4dev, 4k block size, everything on SSD) root@debian:~# /usr/lib/postgresql/8.3/bin/pgbench -c 24 -t 12000 test_db starting vacuum...end. transaction type: TPC-B (sort of) scaling factor: 100 number of clients: 24 number of transactions per client: 12000 number of transactions actually processed: 288000/288000 tps = 2130.734705 (including connections establishing) tps = 2131.545519 (excluding connections establishing) (I wanted to try and see if random_page_cost dropped down to 2.0, sequential_page_cost = 2.0 would make a difference. Eg; making the planner aware that a random was the same cost as a sequential) root@debian:/var/lib/postgresql/8.3/main# /usr/lib/postgresql/8.3/bin/pgbench -c 24 -t 12000 test_db starting vacuum...end. transaction type: TPC-B (sort of) scaling factor: 100 number of clients: 24 number of transactions per client: 12000 number of transactions actually processed: 288000/288000 tps = 1982.481185 (including connections establishing) tps = 1983.223281 (excluding connections establishing) Regards Stef -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAknTxccACgkQANG7uQ+9D9XoPgCfRwWwh0jTIs1iDQBVVdQJW/JN CBcAn3zoOO33BnYC/FgmFzw1I+isWvJh =0KYa -----END PGP SIGNATURE----- -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
