Index Compression Part VI: 12c Index Advanced Compression Block Dumps (Tumble and Twirl)

Richard Foote's Oracle Blog

Sometimes, a few pictures (or in this case index block dumps) is better than a whole bunch of words 🙂

In my previous post, I introduced the new Advanced Index Compression feature, whereby Oracle automatically determines how to best compress an index. I showed a simple example of an indexed column that had sections of index entries that were basically unique (and so don’t benefit from compression) and other sections with index entries that had many duplicates (that do compress well). Advanced Index Compression enables Oracle to automatically just compress those index leaf blocks where compression is beneficial.

If we look at a couple of partial block dumps from this index, first a dump from a leaf block that did have duplicate index entries:

Leaf block dump
header address 216542820=0xce82e64
KDXCOLEV Flags = – – –
kdxcoopc 0xa0: opcode=0: iot flags=-C- is converted=Y
kdxconco 2
kdxconro 651
kdxcofbo 1346=0x542
kdxcofeo 2172=0x87c
kdxcoavs 826

View original post 857 more words


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