Re: Informix tuning
Kai Shen wrote:
>
> Hi,
> we have a 4 CPU, 1GB, SCO 5.0.4 machine running Informix ODS 7.20.UC3.
> onstat -p shows only 74% bufwrites and 94% bufreads. The machine is> running OLTP only and uses Mylex Raid controller. How do I optimize for
> the Mylex? Do the recommendations still hold (number of physical
> disks=CLEANERS etc..)?
In general, poor write cache means that your LRU parameters are too low.
However, your LRU settings must be taken in the context of your
checkpoint activity. If your checkpoints are firing too frequently, then
this will also give you poor write cache performance.
In your case, your checkpoint interval is incredibly low at 60 seconds.
The default is 300 seconds. I would put it back to the default value for
starters and see what happens.
If this value was lowered in order to reduce checkpoint duration, then
look at the LRU parameters in order to solve this problem.
Having said all that, there is nothing wrong with forcing a checkpoint
every minute, but then you must expect your write cache figures to
suffer accordingly.
> We have following settings in $ONCONFIG:
> PHYSFILE 20000
> LOGFILES 30
> LOGSIZE 2048
> MULTIPROCESSOR 1
> NUMCPUVPS 3
> SINGLE_CPU_VP 0
> NOAGE 1
> AFF_SPROC 1
> AFF_NPROCS 3
> LOCKS 300000
> BUFFERS 100000
> NUMAIOVPS 4
> PHYSBUFF 512
> LOGBUFF> LOGSMAX 100
> CLEANERS 4
> LRUS 8
> LRU_MAX_DIRTY 2
> LRU_MIN_DIRTY 1
> SHMTOTAL 0
> CKPTINTVL 60
> LTXHWM 50
> LTXEHWM 60
Hope that helps,
--
Mark.
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