Compression in Oracle, by Jonathan Lewis

http://allthingsoracle.com/compression-oracle-basic-table-compression/

This is an excellent article, with good technical information. The only remark that I have is the remark that Oracle doesn't do compression but deduplication. The problem is, of course, in the fact that compression really is deduplication. If one checks the most popular family of compression algorithms invented by Lempel, Ziv and Welch (that's where "LZW" comes from), one will see that it's all about deduplication. Essentially, those guys are building dictionary of things and, when encounter an existing item, mark it with a pointer. Deduplication and compression are, essentially, one and the same. The description and the fact that Oracle pins the block during the reconstruction are excellent. I really enjoyed reading the article.

-- 
Mladen Gogala
The Oracle Whisperer
http://mgogala.byethost5.com