Re: Long checkpoints (LRU_xxx_DIRTY / LRUS / CLEANERS adapted)
I'm swinging in the dark here, so all the usual disclaimers apply! :-)
Have you tried reducing the checkpoint interval back down to 5 minutes
or so? Perhaps having more frequent checkpoints will make them shorter.
How big is your physical log?
There is a chance that posting your onconfig might reveal something else
to one of the boffins here.
> We are having long checkpoints (around 20 seconds). The number
of
> dirty pages to be written at checkpoint time does not even seem to
> play a major role. Our SUN Sparc Storage Arrays have enough NVRAM
> anyway to handle the chunk writes at checkpoint time. I have
already
> decreased LRU_MIN_DIRTY and LRU_MAX_DIRTY to 2 and 1. I'm now
even
> trying 1 and 0, but this did not decrease the checkpoint duration.
I
> also already increased LRUS from 16 (which is the number of
CPUVPs) to
> 52 and now even 75, again without success. I also increased the
> number of page cleaners to 52 (-> we have about 150 mirrorred
disks).
> Even when there are only 1000 dirty pages, the checkpoint still
takes
> at least 15 seconds. I have been looking at I/O activity during
a
> checkpoint (with iostat -x and the ssaadm utility delivered with
SUN's
> Sparc Storage Arrays), but did not see any overloaded disks at
all.
> When comparing the output from onstat runs before and after the
> checkpoint, I noticed an enormous increase in bufferreads (>
300,000)
> and lockreqs (300,000). Could a high number of bufferread
activity at
> checkpoint time cause this ? Does anyone have another idea ? Any
> help would be welcome as I am already struggling with this for
months.
>
> Thank you in advance,
> Mario Opsomer
>
> PS : We are using a SUN E6000 as db server (18 CPUs). Nothing
else is
> running on that server. KAIO is enabled. BUFFERS is set to
512,000.
> We are running Informix 7.24.UC3 with SAP R/3 (4.0B) as
application.
> I increased CKPTINTVL to decrease the impact of these long
checkpoints
> by decreasing their frequency, but the recovery of a recent crash
was
> so terribly long that I have decreased CKPTINTVL back to 20
minutes.
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