RE: Table compression
- From: Riyaj Shamsudeen <rshamsud@xxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 19 Mar 2004 17:03:33 -0600
Index compression ? These are the two words making my days hell for the
past couple of weeks.
We are in 8.1.7.4 and rely heavily on index compression due to table
size & data properties. Index compression has a bug. CR undo applied to
a compressed index leaf block can corrupt the in-memory buffer throwing
ORA-600[6017]. Problem is that we were not able to reproduce the error
at will and this error happens sporadically. After applying few costly
debug parameters, just yesterday we identified this as bug 2954868 fixed
in 9.2.0.5. Will apply backport fix soon..
If you have high concurrency environment(in the order of 1000s of users
) and if you use index compression heavily, you might want to take a
look at this bug..
Thanks
Riyaj "Re-yas" Shamsudeen
Certified Oracle DBA
This is only my opinion..Does not bind my employer etc..etc..
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Goulet, Dick
Sent: Friday, March 19, 2004 4:39 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Table compression
Humm, that's interesting. Anyone have good commenst to make about index
compression??
Dick Goulet
Senior Oracle DBA
Oracle Certified 8i DBA
-----Original Message-----
From: Khedr, Waleed [mailto:Waleed.Khedr@xxxxxxx]
Sent: Friday, March 19, 2004 4:05 PM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: RE: Table compression
Actually reading from compressed tables is faster than reading from
non-compressed in systems that don't have their CPU's 100 percent busy.
Since the segment size becomes 30% of the original size, the system
requires less IO to read the data.
There is a very little CPU overhead needed to decompress the data.
Compression is done by building lookup tables for repeating values on
the block level.
Regards,
Waleed
-----Original Message-----
From: Goulet, Dick [mailto:DGoulet@xxxxxxxx]
Sent: Friday, March 19, 2004 3:52 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Table compression
Yeah, but what's the penalty during reads???
Dick Goulet
Senior Oracle DBA
Oracle Certified 8i DBA
-----Original Message-----
From: Khedr, Waleed [mailto:Waleed.Khedr@xxxxxxx]
Sent: Friday, March 19, 2004 3:48 PM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: RE: Table compression
I use it, works great, 60% savings.
Once the table/partition gets flagged "compress", any direct load will
be compressed.
You will get ora-600 if trying to do parallel direct load.
Also can't add a column to a compressed table.
Waleed
-----Original Message-----
From: LeRoy Kemnitz [mailto:lkemnitz@xxxxxxxx]
Sent: Friday, March 19, 2004 3:41 PM
To: Oracle List
Subject: Table compression
I am looking into doing some table compression on my warehouse database
to free up some space on the os. I am running 9.2.0.4 on Unix 5.1. The
compression is about 2.5:1 on my tables. The documentation says the
bulk insert time will be doubled but the single inserts, updates, and
deletes are going to be a wash. Does anyone use compression? Are there
any problems you notice in the use of it? I have also read that the
table will need to be re-compressed after the bulk inserts. Any
alternative ideas about getting this done?
Thanks in advance,
LeRoy
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