Re: Best/Only way to change RBS initial/minextents

"Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:YWLm9.45044$g9.128427_at_newsfeeds.bigpond.com...
> "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> news:miLm9.45024$g9.128459_at_newsfeeds.bigpond.com...
>
> ...snip...
>
> >
> > You're doing it hard. What you want to do is to avoid segment growth or
> > shrinkage. Optimal encourages shrinkage (hence, don't set it). And
trying
> to
> > create pretty, perfectly-formed, small rollback segments is likewise an
> > encouragement to growth. If you can spare the disk space, create them
all
> > quite large: say, 6 extents of 8Mb each. If you want your OCP, then 20
> > extents is the right number -and I'd still say they should be each 8Mb
> big.
>
> ... Snip...
>
> > Question 5: What's 1Gb divided by 6 extents? Er, er, er... damn I wished
I
> > passed A level Maths!... er, 180K. Or thereabouts.
> >
> > Therefore: create rollback segement RBS01 storage (initial 180K next
180K
> > minextents 6) tablespace RBS;
> >
>
> Hi Howard,
>
> I agree pretty well agree with what you've said/recommended except I have
a
> question about the above 6 extents suggestion.
>
> Why 6 ? Why not 5, or 8, or indeed 20 extents ?

For the simple reason that extents are recorded in a cluster in the data dictionary that expects no more than 5 extents. Read your sql.bsq.

>
> Personally I usually go for 10 in that 10 is an easier number to use in
any
> calculations, so 10 x 100M (as my maths is always questionable at the
best
> of times ;) It also gives the RBS plenty of time to work it's way around
in
> case of blocking transactions (900M) and increasing in nice healthy chucks
> (100M) to avoid excessive allocations if necessary.
>
> Just curious where you come up with 6 ?

Fair enough. If I was being strict, I should say 5 (see the SIZE parameter for the segment that holds the inserts for UET$ in sql.bsq).

But you're right: in LMT, whatever the size of the UET$ cluster is irrelevant anyway. And besides, the "5" rule only kicks in in the worst possible scenario. If you are the only one doing extent acquisitions on a single segment, then about 180 or so is possible before you start chaining on the UET$ cluster (thank you, Jonathan).

I wouldn't spit the dummy if you said 10.

Anyway, the simple answer as to where I got "6" from is: The Site of Steve Adams (praised be his name). The truth is that it can be a deal more flexible than that, but it doesn't need to be.

However, Connor has different ideas.

Connor????????

Regards
HJR
>
> Cheers
>
> Richard
>
>
Received on Wed Oct 02 2002 - 20:40:01 CDT