FreeLists / oracle-l / Re: Compressing partitions

[Tanel Põder <tanel.poder.003@xxxxxxx>]

Hi,

If you are talking about historical data, which you won't be modifying later 
on, I don't see any real downsides with compression, but with frequently 
modified OLTP data, yes. 

Performancewise, you might want to order your data pysically according your 
main index used in range scans on table as well, that way range scans using 
this index will me more efficient as table rows are physically clustered in the 
order of your index (if performance isn't an issue, then don't bother).

If you want to do physical row ordering, then that's one way to go:

create table temp nologging compress as select * from your_table partition p1 
order by col1,col2,col3;

create index i1 on temp(col1,col2,col3) nosort nologging compress x;
create other indexes... w compress option

alter indexes back to logging (if you want to, for maintenance reasons)

alter table your_table exchange partition p1 with table temp including indexes 
without validation;

alter table your_table modify partition p1 logging;

Also, a very interesting article regarding efficient partition exchanging is 
http://www.dbazine.com/oracle/or-articles/jlewis17
Tanel.

  ----- Original Message ----- 
  From: Kline.Michael 
  To: oracle-l@xxxxxxxxxxxxx 
  Sent: Monday, July 04, 2005 2:57 AM
  Subject: Compressing partitions


  We have several large 2-4 gig partitions on a 5 year basis. After a month or 
two, changes should be almost non-existent.



  They also have partitioned indexes. Just makes things easier when we roll off 
the oldest partition, etc.



  Is there a downside to compression?



  It's sounds like it's supposed to be more stable now, handling tables and 
indexes.



  While I've not found much, it seems like we could expect the 2-4 gig to maybe 
be 200-400 meg??? Even if 25-50% would not be bad given some of it is 5 years 
history.



  We are at 9.2.0.6.



  Michael Kline
  Database Administration
  SunTrust Technology Center
  1030 Wilmer Avenue
  Richmond, Virginia  23227
  Outside 804.261.9446
  STNet 643.9446

  Cell 804.744.1545
  michael.kline@xxxxxxxxxxxx



   


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