Re: Compression in Oracle, by Jonathan Lewis
Date: Thu, 14 Feb 2013 17:24:14 -0000
Message-ID: <Nq-dnXk4xsMlgIDMnZ2dnUVZ8sqdnZ2d_at_bt.com>
"Mladen Gogala" <gogala.mladen_at_gmail.com> wrote in message news:pan.2013.02.10.04.27.09_at_gmail.com...
|I just wanted to share this with the group
|
| 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,
Thanks for mentioning it.I enjoyed writing the series - it was quite nice to have an opportunity to write a fairly lengthy piece (5 instalments) without going to the lengths of writing a book.
You're right about the deduplication / compression thing, of course - at least with respect to loss-less compression mechanism - but I decided to put it the way I did because there's a much higher degree of structure in the choice of deduplication that takes place in an Oracle block than there is in the generic run-count and dynamic dictionary compression methods. I was trying to emphasise the image that there's a significant difference between "compressing an Oracle block" and "compressing a jpg", and the latter is the sort of image that I think many people have in mind when they talk about compression.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com/all-postings
Author: Oracle Core (Apress 2011)
http://www.apress.com/9781430239543
Received on Thu Feb 14 2013 - 18:24:14 CET