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

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@xxxxxxxxxxxxxxxxxx>
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?
>

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