Re: ASSM tablespace three level bmp block questions.

From: Jonathan Lewis <>
Date: Sat, 11 Apr 2009 16:02:42 +0100
Message-ID: <>

"lsllcm" <> wrote in message
> Hi All
> I have one question about ASSM tablespace. The ASSM tablespace has
> three level BMP blocks to
> indicate if block is used. How many blocks does one L1 BMP block
> manages? After do one test, I found
> the number increases when the data increases. Is there any rule about
> it?
> How many L1 BMP blocks does one L2 BMP block manages. After do the
> test, I found the number 241 when
> the blocksize is 2048 bytes. Is that right?
> Any answers are appreciated.

I don't think there is any public documentation of such things, and given the apparent flexibility of the algorithms I don't think you can expect a solid answer.

Your 241 L1's per L2 in a 2KB block looks about right since an L1 reference seems to be 8 bytes when you dump an L2,

The number of blocks referenced by an L1 BMB depends on the extent sizes and the block sizes - larger extents lead to more blocks more L1 BMB, for example I have a 64MB extent size with an 8KB block that gives 256 blocks
per L1 BMP. An entry in an L1 block needs only 4 bits - so an single L1 block could reference far more that the 1024 data blocks that Tanel quotes in his presentation , but I'd guess that the actual number is restricted to avoid
excessive content on L1 blocks.


Jonathan Lewis

Author: Cost Based Oracle: Fundamentals

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Received on Sat Apr 11 2009 - 10:02:42 CDT

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