Re: High IOWAIT times, low iops? Need Help with configuration
От | Evan Reiser |
---|---|
Тема | Re: High IOWAIT times, low iops? Need Help with configuration |
Дата | |
Msg-id | 5f33a0cb0706280617y3ae9d4a2ud338c076d8bf38f0@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: High IOWAIT times, low iops? Need Help with configuration (Richard Huxton <dev@archonet.com>) |
Список | pgsql-performance |
we've tried benchmarking the array, the data array can write at 800mb/s for files less than 256mb (raid write cache), after which it can sustain 300mb/s, it seems like it can also handle 6-700 iops when benchmarking. it seems to work as expected outside of postgres, I guess we can look at the drivers, let me know if you guys have any other suggestions, thanks for your help, -evan On 6/28/07, Richard Huxton <dev@archonet.com> wrote: > Evan Reiser wrote: > > I was wondering if you guys have some suggested settings for our server, i > > think we are not hardware limited but the configureation is set up > > incorrectly. For some reason our database seems to have trouble handling > > 10+ inserts per second which seems to be a pretty trivial load for this > > hardware, we're seeing very high %iowait, this is a pretty typical output > > for #iostat -m 5 > > > > avg-cpu: %user %nice %system %iowait %steal %idle > > 0.41 0.00 0.41 96.28 0.00 2.90 > > > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > > sda 90.63 0.08 0.56 0 2 > > sdc 0.00 0.00 0.00 0 0 > > sdd 94.09 0.19 1.74 0 8 > > > > > > sda = 2x320GB 7200rpm in RAID1 > > sdc = 2x150GB 10krpm in RAID1 (transaction log is on this array) > > sdd = 6x150GB 10krpm in RAID 10 (database is on the array) > > OK, so no write activity on the transaction log, and hardly any reading > on sdd. Your disks are practically idle, and yet iowait is at 96% - very > strange. > > > raid controller = 3ware 9650 12port - 256MB cache > > > > 8GB RAM, core 2 duo - quad core > > > > it would seem like the io subsystem is the limiting factor, but i feel > like > > we should be barely hitting a wall, you can see from the example its > > writing > > < 2MB/s to the array > > > > Here's some of our settings > > > > shared_buffers = 256MB # min 128kB or > max_connections*16kB > > temp_buffers = 32MB # min 800kB > > max_prepared_transactions = 50 # can be 0 or more > > work_mem = 32MB # min 64kB > > maintenance_work_mem = 32MB # min 1MB > > max_stack_depth = 7MB # min 100kB > > > > max_fsm_pages = 512000 # min max_fsm_relations*16, 6 bytes > > Well, you might want to tweak these, but they're not going to completely > kill your io. > > > fsync = off # turns forced synchronization > > You'll be turning this back on in production, I take it? > > Hmm - ideas > 1. Run a VACUUM FULL on your database(s) and see what happens with your > io then > 2. Test a block copy, something like (but a directory on sdd): > dd if=/dev/zero of=/tmp/empty count=1000000 > That should show an upper limit for your write speed. > 3. Google around and check there aren't any issues with your raid > controller and kernel/driver versions. > > -- > Richard Huxton > Archonet Ltd >
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