Re: LMT advice

From: Howard J. Rogers <howardjr2000_at_yahoo.com.au>
Date: Sat, 27 Sep 2003 00:12:24 +1000
Message-ID: <3f744a00$0$28898$afc38c87@news.optusnet.com.au>

Daniel Morgan wrote:

>>>

> You've almost got me convinced. So now what is the difference in
> overhead between using autoallocate
> pushing out multiples of 64K 1000 times per hour and one large extent
> per hour when working with a
> table doing a large number of inserts? Aren't we talking about more hits
> on the bitmap which means
> writes to the datafile's header?
>

I don't follow. There's 64K of tablespace bitmap (ie, 8 blocks on an 8192 bytes blocksize systen). If you want to allocate an 8M extent to a segment (and bear with me on my maths here) you simply have to flip 128 bits in one of the bitmap blocks. If you want to allocate a 64K extent, you just flip one bit.

Your table still gets 8M extents, or 64M extents or whatever, as far as its concerned. It's just the number of bits which get flipped to record thOse different extent sizes that changes.

The difference in workload between flipping 128 bits and 1 bit is not going to be measurable. There's no real extra I/O involved in the one case as compared to the other.

Regards
HJR Received on Fri Sep 26 2003 - 09:12:24 CDT