[mythtv-users] IOBOUND during mythfilldatabase

[Chris Strom]

On 2/23/07, Glenn <glenn at saskatoon.com> wrote:
> I've searched through the mailing list without finding any good resolution to
> my problem.  This sounds similar but the ticket was closed as invalid:
>
> http://www.mythtv.org/pipermail/mythtv-commits/2005-September/007946.html
>
> This is what is happening.  When mythfilldatabase runs the backend logs these
> types of errors:
> 2007-02-23 13:14:33.947 TFW, Error: Write() -- IOBOUND begin cnt(2048)
> free(2047)
> 2007-02-23 13:14:37.074 TFW, Error: Write() -- IOBOUND end
>
> Sometimes it just becomes unresponsive while at other times it actually
> crashes and I have to restart it.
>
> I don't believe that it is just a system performance issue but could certainly
> be related to some settings or configuration.  My original backend server was
> a dual PII - 333MHz with 192MB ram.  It worked perfectly though a little slow
> for commercial flagging, etc.
>
> I recently upgraded to a Athlon 64 - 3200 with 1GB of ram. I kept the same
> drives (Seagate 160GB in Raid 1).  I am using ext3 and dma seems to be turned
> on.  I installed fedora core 6 at the same time as the hardware change and
> moved to myth 0.20.  I should point out the I am recording 1 stream on a
> PVR500 and that this is a BE only.  During normal recording I see mythbackend
> only uses 1-2% cpu.
>
> If I look in top during mythfilldatabase I can see as much as 95% wa.
>
> What direction should I look in?  Is this a disk bandwidth problem?  A mysql
> problem?

The wiki has some hints on troubleshooting IOBOUND issues.  You might
also check the varous mysql buffer sizes.  For a reference point, here
is what I use (not my entire conf, just the parts related to buffers):

[mysqld]
skip-locking
key_buffer = 256M
max_allowed_packet = 1M
table_cache = 256
sort_buffer_size = 4M
read_buffer_size = 1M
read_rnd_buffer_size = 4M
myisam_sort_buffer_size = 64M
thread_cache = 8
query_cache_size= 16M

innodb_buffer_pool_size = 64M
innodb_additional_mem_pool_size = 8M
innodb_log_file_size = 5M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 1
innodb_lock_wait_timeout = 50


-Chris