Messages in this thread | | | Date | Tue, 19 Nov 2002 01:40:31 -0800 | From | Andrew Morton <> | Subject | Re: Machine's high load when HIGHMEM is enabled |
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vasya vasyaev wrote: > > Hi again, > > Let me try to explain what is this all about... > > Box has 1 GB of RAM, it's running oracle database. > After some disk activity disk cache has 400 Mb, so 600 > Mb is free
And the other 400 megabytes will be freed up on demand.
> Oracle is tuned for using of 800 Mb of RAM for SGA (as > shared memory segment), so Oracle needs 800 Mb of RAM > to be free before it's start, right ?
No... If that were so, you'd never be able to start any applications.
> So when oracle starts it can't allocate this 800 Mb > for SGA and fails to start...
Well, maybe Oracle is failing to start. But maybe that's not for the reasons you are assuming.
> Where is a problem - in kernel which can't reduce disk > cache to allow allocating of shared memory segment or > in oracle ?
If Oracle requests 800 megabytes from the kernel, it will get it. It won't be able to mlock it (I'm guessing here).
> BTW, free doesn't show that shared memory is in use > when oracle is started and requested shared memory > segment is allocated (and ipcs shows it).
Yup, the "shared" accounting is always zero. Maybe we should fix that, or remove it.
> We need to control disk cache to reduce it as much as > possible because it's not needed for oracle, much > better is to allow oracle to control the RAM > for it's use. > > As to compare, on solaris we mount ufs with > "forcedirectio" mount option, which tells not to use > disk cache.
Please ensure that the failure is not some Oracle-specific setup thing, and then provide specific details on the problem which you are observing. The assumptions which you are making may not be correct.
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