Re the space savings: that may or not be important. Guess it depends on
how tight storage space is in your environment, and how much of an impact
it may make on your backups.
Re the performance: Some queries could perform better due to the index
data being packed into fewer blocks, as you are expecting.
It could also result in decreased performance for inserts, for the same reason.
An index with all data tightly packed into nearly full blocks makes it a good
candidate for excessive block splits when data is inserted into the table.
You could allow a generous PCTFREE when you rebuild to alleviate this, but
then there would not be much point in rebuilding the index.
You might consider targeting your most expensive operations ( eg. the SQL
that causes the users and/or the system the most pain ) and then look at
the indexes involved to see if rebuilding them would increase or decrease
performance.
Lots of discussion lately on this list on how to go about doing that.
( Optimizing Oracle Performance - http://www.oreilly.com/catalog/optoraclep/ )
HTH
Jared
| renu r <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED] 11/06/2003 02:29 PM
|
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> cc: Subject: Re: any problem rebuilding indexes used for replication |
Jared : I think it is fragmented based on scripts and knowing that there have been lot of deletes.
One script uses the table index_stats and looks at field del_lf_rows which should be less at least in comparison to field lf_rows. I mean less is good. more bad. I am not sure about the script but I will post it here if someone says so or send it to anyone if they want.
I am sure the experts here know about it and can clarify if it is any good to look at the index_stats table.
One other simple useful script is :
SELECT owner, index_name, blevel
FROM all_indexes
WHERE blevel > 2
This can be bacause the size of table is big so it is not definitive. I will check the level after rebuild.
Benefits expected : Space savings (definitely). performance (hopefully). I will let you and Yong know about the benefits if any. If I get some help.
[EMAIL PROTECTED] wrote:
I'm curious, how have you identified the fragmentation?
What benefits do you expect from the rebuild of the indexes?
Are you targeting certain indexes that have been identified as
benefiting from a rebuild, or just planning to rebuild all indexes?
Jared
| renu r <[EMAIL PROTECTED]> Sent by: [EMAIL PROTECTED] 11/05/2003 06:14 PM | To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> cc: Subject: any problem rebuilding indexes used for replication |
Hello,
I have to rebuild some primary key indexes due to excessive fragmentation. It is rebuild not drop and create. We have multi master replication running. Is there any problem to replication if I do that. Has anyone tried it? TIA.
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