"Howard J. Rogers" <hjr_at_dizwell.com> wrote in message
news:41b75a73$0$12876$afc38c87_at_news.optusnet.com.au...
> Richard Foote wrote:
>> "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.
>
> "dubious"... it's not a very scientific word, is it?! "28% of my buffer
> cache consumed by ASSM BMBs"... that's a bit more like it (I think it was
> Jonathan that posted that once... I hope he will clarify), and would
> qualify as significant in anyone's book, surely.
>
Hi Howard,
Oh, I don't know, I think scientists can get away with the word "dubious":
"It's worked, it's worked, my monster with the unattractive bolt through the
neck is alive although it's dubious whether he'll find a long term, happy
relationship" !!
As for your point, I think it a little dubious to question my wording on
something (lots of extents in a non ASSM tablespace) and then refer to a
totally different example (ASSM).
Dubious indeed !!
As for ASSM, zzzzzzzzzzzzzzzzzzzz, been there discussed that, re-read
through the archives on why it may not *always* be evil.
BTW, is evil a scientific word ?
Cheers ;)
Richard
Received on Wed Dec 08 2004 - 14:26:23 CST
