Hi Vikas,
In simple words, a block split happens when an INSERT needs to add an entry
into a leaf block and finds it full, requiring it to 'split' and balance
itself by migrating half the index entries into the new block (at's why it's
called a B Tree or 'Balanced' tree). More details in the oh-so-rarely-read
Server Concepts manual...
As far as specific events go, you may need to look at 'latch free' waits -
trace the p2 values from v$session_wait (usually 'cache buffer chains')
using the following sqls
select event, count(*) from v$session_wait
group by event
select p2, count(*) from v$session_wait
where event = 'latch free'
group by p2
select * from v$latchname where latch# in (<list of latches>)
V$SYSTEM_EVENT will tell about the system as a whole while V$SESSION_WAIT
will tell you what that particular process is waiting for. Are many INSERTs
doen in parallel? There could also be an issue with FREELISTS (that's a
different ballgame altogether).
What you should probably do is to investigate your 'Index badness' using the
following:
ANALYZE INDEX &&index_name VALIDATE STRUCTURE;
col name heading 'Index Name' format a30
col del_lf_rows heading 'Deleted|Leaf Rows' format 99999999
col lf_rows_used heading 'Used|Leaf Rows' format 99999999
col ibadness heading '% Deleted|Leaf Rows' format 999.99999
SELECT name, del_lf_rows, lf_rows - del_lf_rows
lf_rows_used,
to_char(del_lf_rows / (lf_rows)*100,'999.99999') ibadness
FROM index_stats where name = upper('&&index_name');
undefine index_name
As a rule of thumb if 10-15% of the table data changes, then you should
consider rebuilding the index.
Hth,
John Kanagaraj
Oracle Applications DBA
Hitach Data Systems, Santa Clara
Work : (408) 970 7002
>-----Original Message-----
>From: Vikas Kawatra [mailto:[EMAIL PROTECTED]]
>Sent: Tuesday, May 08, 2001 10:52 AM
>To: Multiple recipients of list ORACLE-L
>Subject: RE: Inserts slowing down on OLTP systems
>
>
>What specific events should I look for in these tables ! -
>atleast the imp
>ones -
>And What's a block split ?
>
>vikas
>
>-----Original Message-----
>Sent: Tuesday, May 08, 2001 6:32 AM
>To: Multiple recipients of list ORACLE-L
>
>
>instead of checking hit ratios, try looking at wait events in
>v$session_event, v$system_event and v$session_wait.
>
>also -- how many indexes are on these tables? How much data is in the
>tables? If the indexes are doing constant block splits on the
>insert you are
>
>basically rebuilding the index each time.. this can have a
>major impact on
>performance.
>
>Rachel
>
>
>>From: Vikas Kawatra <[EMAIL PROTECTED]>
>>Reply-To: [EMAIL PROTECTED]
>>To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
>>Subject: Inserts slowing down on OLTP systems
>>Date: Mon, 07 May 2001 16:55:28 -0800
>>
>>Anyone have ideas on why OLTP database inserts would slow
>down by 100% from
>>levels 15 days ago ?
>>
>>We alreay checked hit ratios in shared pool , checked for any storage
>>issues
>>etc
>>
>>thanks
>>
>>vikas
>>--
>>Please see the official ORACLE-L FAQ: http://www.orafaq.com
>>--
>>Author: Vikas Kawatra
>> INET: [EMAIL PROTECTED]
>>
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>Author: Vikas Kawatra
> INET: [EMAIL PROTECTED]
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