Re: ASSM tablespace three level bmp block questions.

>> Here is a good start...
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The last thing I have seen on this level of information is: "Oracle does not publish the internals of space management" - This was one of the "features" Oracle obtained when they purchased the DEC/Rdb product. IIRC there was a particular patent that is used to make all of this work. If you can find some of the old DEC/Rdb internals manuals, you may get a better idea of how this works. In Rdb, you could actually set the SPAM interval. There are Area Inventory pages (AIP), "Area" bitmaps (aka tablespace bitmaps aka ABM) and SPAce Management bitmaps) and Data pages. A data page was 1-to-n multiple of the disk block size. So, in VMS all data on disks were stored in 512byte blocks. A "page size" (configurable) of 1024 was 2 disk blocks. The SPAM interval (in Rdb) was the number of data_pages per SPAM page. On disk if the DATA:SPAM was 100, you would have a SPAM page followed contiguously as possible by 100 data pages of size 1024bytes. The ability to size these very small was to reduce high volume insert contention. In the Oracle/RDBMS implementation a data page is know as an extent (they didn't want to confuse the masses with new terminology.) They also seemed have changed the terminology of the SPAM "threshold" (fullness value) and when it should "consider" adding more data to this page (pctfree/used concept).

One other note, there are some additional differences and possibly new concepts (as stated, none of this is actually published out side of Oracle) in the current ASSM implementatin but this is what happens when the best minds in the database engine arena get together. Received on Wed Apr 01 2009 - 09:52:06 CDT