Re: Decyphering LMT space bitmap

From: Madhavan Amruthur <mad5698_at_lycos.com>
Date: Mon, 08 Apr 2002 12:53:31 -0800
Message-ID: <F001.0043EF37.20020408125331@fatcity.com>

Hi Jeremiah,

>How is the LMT bitmap organized?

I did some research about the bitmap structure for an LMT tablespace a while ago.

The first 2 blocks are

Block 1 - For File Header
Block 2 - For File Space Bitmap Header

The bitmap itself is stored in 6 blocks after that , blocks 3 thru 8. Each of the bit tracks four extents represented by an F (hex for 15).

0000000000000000 0000000000000000 0000000000000000 00000000000000000

For eg: if you create a table with 1 extent

then there will be a 1 which 1 2 to the power of 0 = 1  and if there 2 extents then its 2^0 + 2^1 = 3

for 4 extents its 2^0+2^1+2^2+2^3 = 15 =F so the values will be either 0,1,3,7,or F for each bit.

In your case

FFFFFF3F00000000 0000000000000000 0000000000000000 00000000000000000

there are 7 F's = 7*4 = 28 extents + 2 (represented by the 3) and = 30.

The rest are 0's because there is no data yet as there are only 30 extents. Each of these blocks 129024 extents.

When I did my test and I had raised the question at that time that the max data that can be stored is 129024 * 6 (blocks) = 774144 extents and if the extent size for argument is 1K then the max size the bitmap can track is 774144K or 7M data file. I have not found an answer yet.

You will find that there are about 504 lines of 64 bits each.

I have a detailed record of the test if you are interested that I can mail to you.

Hope this helps.
Regards,

---

Madhavan Amruthur

See Dave Matthews Band live or win a signed guitar http://r.lycos.com/r/bmgfly_mail_dmb/http://win.ipromotions.com/lycos_020201/splash.asp

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Author: Madhavan Amruthur
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Received on Mon Apr 08 2002 - 15:53:31 CDT