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Re: High IOWAIT times, low iops? Can't figure out what the bottleneck is...

From: "Evan Reiser" <evan(dot)reiser(at)gmail(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: High IOWAIT times, low iops? Can't figure out what the bottleneck is...
Date: 2007-07-03 17:44:49
Message-ID: 5f33a0cb0707031044k71811735ye51a3b0dc25638e2@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-admin
Here is the table structure for the table with all the inserts

id(PK)        integer
dateinserted  datetime without timezone
dateexamined  datetime without timezone
lockedby      integer
done          boolean
failed        boolean
invalid       boolean


>select * from table limit 1;
id      | done | failed |     dateinserted    | dateexamined   | lockedby |
invalid
--------+------+--------+---------------------+----------------+----------+---------
3130902 | f    | f      | 1900-01-01 00:00:00 |                |        0 |
f

There is a clustered index on dateinserted,
+ a non clustered index on id
+ a non clustered index on done,failed,invalid
+ a non clustered index on lockedby

There are no triggers



On 7/3/07, Evan Reiser <evan(dot)reiser(at)gmail(dot)com> 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
> 5-10+ 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
>                 0.97      0.00    0.82         89.69     0.00      8.52
>
> Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
> sda              85.40         0.18         0.72
> 0                3
> sdb               0.00         0.00         0.00
> 0                0
> sdc              30.43         0.00         0.76
> 0                3
> sdd              93.91         0.71         0.12                 3
>        0
>
>
>
>
> sda = 2x320GB 7200rpm in RAID1 (operating system)
> sdc = 2x150GB 10krpm in RAID1    (transaction log is on this array)
> sdd = 6x150GB 10krpm in RAID 10 (database is on the array)
>
> we're using ReiserFS on each of the arrays as the file system
> OS is debian Etch x64
>
> raid controller = 3ware 9650 12port - 256MB cache
>
> 8GB RAM, core 2 duo - quad core 2.4ghz 8MB L2 Cache
>
> 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.  If i try to copy a big file (1-2GB) over to
> the array, the array hits 300MB/s sustained, it can burst write files <
> 256mb AT 800MB/S
>
> Here's some of our settings
>
>
> shared_buffers = 1024MB
> temp_buffers = 32MB
> max_prepared_transactions = 50
> work_mem = 64MB
> maintenance_work_mem = 256MB
> max_stack_depth = 7MB
> max_fsm_pages = 512000
>
> vacuum_cost_delay = 20ms
>
> fsync = on
> wal_buffers = 1MB
> checkpoint_segments = 32
>
> effective_cache_size = 4128MB
>
> If you guys have any suggestions it would be greatly appreciated
>
> -Evan Reiser
>

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