Re: why shrink rollback segs?

Thanks.. makes sense...
Can I use x$bh or something to determine whether it's nicely squeezed into the buffer at some point in time?

On Mon, 12 Nov 2001 02:00:21 -0800, you wrote:

>If rb's are small, then there is a good chance that
>just when they are about to aged out of the buffer
>cache, hey presto! another session needs them again -
>so you end up with a nice scenario where they spend
>their life in the cache and cause virtually no IO.
>
>As they get larger and larger, the time-before-reuse
>time gets longer and longer - which will mean more and
>more IO. Its the same for having lots of extents -
>many moons ago this used to be due to txns needing
>their own extents. Oracle lifted this restriction
>somewhere in v7, but it still makes sense to have 20
>or so extents, because then when a rollback segment
>increases in size, it does it in nice 5% increments -
>keeping the probability of it all fitting in the cache
>high.
>
>hth
>connor
>
> --- Doug C <dcowles_at_i84.net> wrote: > OK.. this may
>be a little naive..and maybe I'm just
>> jogging my own memory, but
>> here it goes...
>> There are a couple schools of thought on rollback
>> segments as near as I can
>> figure. Some like to set optimal, and some don't.
>> The one's that don't like
>> to shrink them at night or once daily or some other
>> variation..
>>
>> Question: Why bother? If they get big and you have
>> the room, so what? They
>> won't have to extend tomorrow, no? If you're
>> concerned about space, why not set
>> a good maxextents or a limit on the filesize..
>>
>> What's the problem with them getting large?
>>
>> Thanks,
>> Doug
>>
>>
>>
>>
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Author: Doug C
  INET: dcowles_at_i84.net

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