I/O or Threading Suffer

[Scott Long]

jesk wrote:
> hello,
> 
> i got problems with mysql under freebsd 5.2.1 and CURRENT.
> 
> i got these problems on two machines with different hardware, but both are
> single cpu machines.
> used scheduler is ULE.
> 
> problem description:
> under high i/o load the mysqld isnt responding any more.
> i tested this with dd if=/dev/urandom of=testfile bs=128k on the hdd an was
> not
> able to become any ouput from simple select-statements within a long period
> of time
> (above minutes).
> i dont know if this problem occurs from mysql and its threads or if the i/o
> subsystem has
> any problems to deal fast enough with two intensives read and write
> processes and its
> priorities.
> 
> best regards,
> christian
> 

If you are dd'ing from /dev/random, then you are depleting the entropy
pool.  Anything else that tries to get random numbers is going to block
in strange ways.  Trying just dd'ing from /dev/zero and see if that
makes a difference.

Scott