Re: Causes for "Enq: TM - contention" on a table with conventional path insert?

Hmmm, I think that the logical possibility of an insert into any partition would defeat the purpose, and the lock would be held at the table level.

• Original Message ---- From: Mark Brinsmead <pythianbrinsmead_at_gmail.com> To: riyaj.shamsudeen_at_gmail.com Cc: david_at_david-aldridge.com; Oracle List <oracle-l_at_freelists.org> Sent: Thursday, May 15, 2008 9:45:02 PM Subject: Re: Causes for "Enq: TM - contention" on a table with conventional path insert?

It may not be as complicated as that. Check the documentation on multi-table inserts.

I have no idea whether or not a multi-table insert will avoid the bottleneck, but the O.P. might at least find that it provides a convenient way to encode which rows should be inserted into which partitions. Of course, if there are hundreds of partitions, the coding could drive you insane, and I am pretty sure that somewhere there is a maximum length for a SQL statement. (40,000 bytes?)

Just a thought...

On Thu, May 15, 2008 at 2:26 PM, Riyaj Shamsudeen <riyaj.shamsudeen_at_gmail.com> wrote:

David

1. Is it possible to modify insert statement to specify partition name ? using bind variables, it may be possible to deduce partition name. insert into target_table partition (pname) ..

      This can be done using dynamic SQL.

 2. Are you sure insert statement is executing serially? No parallelism involved here? I have seen few parallel DML operations acquiring exclusive lock on the table. Trace or explain plan to see whether paralellism in play or not?

Cheers
Riyaj Shamsudeen
The Pythian Group :www.pythian.com
orainternals.wordpress.com

On Thu, May 15, 2008 at 3:17 PM, David Aldridge <david_at_david-aldridge.com> wrote:

Folks,  

I have a situation like this:  

10.2.0.2 EE on Sparc 64bit  

An insert statement of the form ...  

INSERT INTO target_table

            (...)
   SELECT /*+ ORDERED FULL (t1) FULL(t2) FULL(t3) */

          ...
     FROM t1, t2, t3, t4
    WHERE t1.col1 = t2.col2
      AND t1.col3 = t3.col4
      AND t1.col1 >= :b2 
      AND t1.col1 < :b1

The target table is range partitioned with 8 ranges, and 8 copies of the above query run simultaneously to load the table using different :b1 and :B2 values. Each statement loads a single partition but the optimizer has no way of deducing that fact. (Not my design!)  

There are no indexes on the table at the time of load.  

There are no constraints on the table at all.  

Oracle is serializing the inserts so that only one session can insert into the target table at a time. I would expect this if I was performing direct path load, maybe if there were bitmap indexes, or if there were FK's involved perhaps, but I've ruled out all of those.  

V$SESSION_WAIT shows the following:  

SID: 394
SEQ#: 79
Event: enq: TM - contention
P1TEXT: name|mode
...
P1RAW: 00000000544D0006 -- ie. a TM Exclusive?  

.. and the P2 parameter gives the object_id for the target table in the insert statement  

So I'm a bit at a loss to know what else could cause this, or what tests to run next time i execute this process in order to get more data to help analyze it.  

Thoughts?

--

Cheers,
-- Mark Brinsmead

Senior DBA,
The Pythian Group
http://www.pythian.com/blogs
--

http://www.freelists.org/webpage/oracle-l Received on Thu May 15 2008 - 21:09:07 CDT