Re: type of striping

"Noons" <wizofoz2k_at_yahoo.com.au> wrote in message news:1102498989.134881.223450_at_f14g2000cwb.googlegroups.com...
> Howard J. Rogers wrote:
>
>>
>> Because if you choose your uniform size poorly (ie, too small), then
> the
>> number of extents a segment acquires will shoot up. And the ASSM
> bitmaps
>> get more burdensome the more extents they have to manage/deal with.
>
> Yes, but that would be the case as well with LMT without ASSM,
> wouldn't it? I mean, it uses a bitmap as well to allocate
> space in uniform extents. Too small an extent, too large a bitmap,
> *potential* problem. Does it get compounded with ASSM?
>

Hi Nuno,

It's been a while since I've looked at all this in any detail and I don't have time to research my research (I've a new Pink Floyd DVD to investigate :) but to briefly answer your questions.

The ASSM bitmaps reference *blocks* not extents and as such bitmaps can be stored in one block and yet reference/span a number of smaller extents or can be stored in several blocks in order to reference the blocks in one larger extent. However, the ratio of bitmap blocks to referenced blocks can be higher for smaller extents sizes although there are quite a number of ifs and buts with it all (for example results varied between uniform and autoallocate).

With regard to LMT without ASSM and the *extent* management bitmaps of LMT, note that Oracle allocates a number of blocks (64Kish) in the first datafile of the tablespace regardless so providing these blocks are sufficient to map all extents in the tablespace, then extent size doesn't really matter. If however you have a massive tablespace with a smaller extent size, then Oracle may need to allocate additional bitmap blocks in the tablespace, where it's again dubious whether such an overhead is significant to really matter as well.

Cheers

Richard Received on Wed Dec 08 2004 - 05:35:02 CST