Re: Question about Append hint in Insert

Mark,

APPEND stops table UNDO, not table REDO.
That point often gets hidden because the hint
is used so often in conjunction with nologging tables.

Otherwise your comments are correct - the benefit
applies only to the table segment, and you get the
exclusive table lock.

There is some potential for benefit on the indexes
because the index entries are per-sorted before 
inserting, and there is an optimization that reduces
undo and redo if multiple rows goes into a single
leaf block.

There is some downside on the table because the
HWM is bumped for the append, so you could
leave a trail of empty space behind you as you 
do lots of appends - but at 1,000 rows per insert,
the percentage waste of space is likely to be small.

Regards

Jonathan Lewis

http://www.jlcomp.demon.co.uk

http://www.jlcomp.demon.co.uk/faq/ind_faq.html
The Co-operative Oracle Users' FAQ

http://www.jlcomp.demon.co.uk/seminar.html
Optimising Oracle Seminar - schedule updated May 1st


----- Original Message ----- 
From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, June 18, 2004 8:06 PM
Subject: RE: Question about Append hint in Insert


Harvinder,

1.)  Should be no real disadvantage, other than an exclusive lock on the
table.  More on that later.
2.)  Hint will only apply to table.  Any index updates that result from
table load will always log.  If you want to, you could alter index ...
unusable, then do the load, then alter index ... rebuild nologging;
3.)  The problem here is that an INSERT /*+ APPEND */ takes an
*exclusive* lock on the table.  This prevents any other DML from running
on the table till that transaction commits.  The second process will
wait on the exclusive mode TM enqueue that the first process is holding.

Hope that helps,

-Mark

Mark J. Bobak
Oracle DBA
ProQuest Company
Ann Arbor, MI
"Post Hoc Ergo Propter Hoc"


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Harvinder Singh
Sent: Friday, June 18, 2004 2:43 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Question about Append hint in Insert


Hi,

We are testing insert performance in one of out tables and we are
selecting from 1 table 1000 rows at a time and inserting in 2nd table.
So we were getting tps of about 17000 for 1 million records. Then I
added append hint to insert and tps went up to 23000. Now if I a try to
insert from 2 clients to increase scalibility both insert at tps of
11000. so I have 2 questions:
1) What is the disadvantage of adding append hint during insert (we
never delete or update this table in production)
2) Will the hint applicable to all the indexes or only table
3) Why with 2 clients using append result in less tps than normal 2
client inserts?

Thanks
--Harvinder
=3D20



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