Re: Testing Sandforce SSD

Greg Smith wrote:
> Put it on ext3, toggle on noatime, and move on to testing. The
> overhead of the metadata writes is the least of the problems when
> doing write-heavy stuff on Linux.
I ran a pgbench run and power failure test during pgbench with a 3 year
old computer

8GB DDR ?
Intel Core 2 duo 6600 @ 2.40GHz
Intel Corporation 82801IB (ICH9) 2 port SATA IDE Controller
64 bit 2.6.31-22-server (Ubuntu karmic), kernel option elevator=deadline
sysctl options besides increasing shm:
fs.file-max=327679
fs.aio-max-nr=3145728
vm.swappiness=0
vm.dirty_background_ratio = 3
vm.dirty_expire_centisecs = 500
vm.dirty_writeback_centisecs = 100
vm.dirty_ratio = 15

Filesystem on SSD with postgresql data: ext3 mounted with
noatime,nodiratime,relatime
Postgresql cluster: did initdb with C locale. Data and pg_xlog together
on the same ext3 filesystem.

Changed in postgresql.conf: settings with pgtune for OLTP and 15 connections
maintenance_work_mem = 480MB # pgtune wizard 2010-07-25
checkpoint_completion_target = 0.9 # pgtune wizard 2010-07-25
effective_cache_size = 5632MB # pgtune wizard 2010-07-25
work_mem = 512MB # pgtune wizard 2010-07-25
wal_buffers = 8MB # pgtune wizard 2010-07-25
checkpoint_segments = 31 # pgtune said 16 here
shared_buffers = 1920MB # pgtune wizard 2010-07-25
max_connections = 15 # pgtune wizard 2010-07-25

Initialized with scale 800 with is about 12GB. I especially went beyond
an in RAM size for this machine (that would be ~ 5GB), so random reads
would weigh in the result. Then let pgbench run the tcp benchmark with
-M prepared, 10 clients and -T 3600 (one hour) and 10 clients, after
that loaded the logfile in a db and did some queries. Then realized the
pgbench result page was not in screen buffer anymore so I cannot copy it
here, but hey, those can be edited as well right ;-)

select count(*),count(*)/3600,avg(time),stddev(time) from log;
count | ?column? | avg | stddev
---------+----------+-----------------------+----------------
4939212 | 1372 | 7282.8581978258880161 | 11253.96967962
(1 row)

Judging from the latencys in the logfiles I did not experience serious
lagging (time is in microseconds):

select * from log order by time desc limit 3;
client_id | tx_no | time | file_no | epoch | time_us
-----------+-------+---------+---------+------------+---------
3 | 33100 | 1229503 | 0 | 1280060345 | 866650
9 | 39990 | 1077519 | 0 | 1280060345 | 858702
2 | 55323 | 1071060 | 0 | 1280060519 | 750861
(3 rows)

select * from log order by time desc limit 3 OFFSET 1000;
client_id | tx_no | time | file_no | epoch | time_us
-----------+--------+--------+---------+------------+---------
5 | 262466 | 245953 | 0 | 1280062074 | 513789
1 | 267519 | 245867 | 0 | 1280062074 | 513301
7 | 273662 | 245532 | 0 | 1280062078 | 378932
(3 rows)

select * from log order by time desc limit 3 OFFSET 10000;
client_id | tx_no | time | file_no | epoch | time_us
-----------+--------+-------+---------+------------+---------
5 | 123011 | 82854 | 0 | 1280061036 | 743986
6 | 348967 | 82853 | 0 | 1280062687 | 776317
8 | 439789 | 82848 | 0 | 1280063109 | 552928
(3 rows)

Then I started pgbench again with the same setting, let it run for a few
minutes and in another console did CHECKPOINT and then turned off power.
After restarting, the database recovered without a problem.

LOG: database system was interrupted; last known up at 2010-07-25
10:14:15 EDT
LOG: database system was not properly shut down; automatic recovery in
progress
LOG: redo starts at F/98008610
LOG: record with zero length at F/A2BAC040
LOG: redo done at F/A2BAC010
LOG: last completed transaction was at log time 2010-07-25
10:14:16.151037-04

regards,
Yeb Havinga