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Don Burleson Blog 







enq: TX - allocate ITL entry tips

Oracle Database Tips by Donald BurlesonUpdated July 22,  2013

Question:  I am seeing a batch update job waiting excessively for the enq: TX - allocate ITL entry wait event.  This is a parallel batch stream with multiple concurrent update processes being spawned.

Answer:  The event "enq: TX - allocate ITL entry" indicates "enqueues" (locks) that are waiting for serial access to Oracle resources, in this case the transaction is waiting for a lock that is held by a competing session.

This "enq: TX - allocate ITL entry" indicates error is seem when too many concurrent DML transactions are competing for the same data block.

The ITL in the "enq: TX - allocate ITL entry" indicates error is for "Interested Transaction List", and there are several approaches to fixing this error:

1 - Increasing the value of INITRANS and/or MAXTRANS for the table and indexes.

2 - Move the table to a smaller blocksize.

3 - In some cases, you can remove the enq: TX - allocate ITL entry error for UPDATE/DELETE DML issues by reorganizing the table to increase PCTFREE for the table, thereby leaving less rows per data block.

4 - Reduce the degree of parallel DML on this table

The P1, P2 and P3 values for enq: TX - allocate ITL entry also give details about the origin of the wait event.

Wait Class P1 P2 P3
enq: TX - allocate ITL entry Configuration name|mode usn<<16 | slot sequence

Finding the object causing the wait 

Here is a query to display the object from the 'enq: TX - allocate ITL entry' wait event (you must have an ASH license to run this SQL script):


   lpad(round(ratio_to_report(count(*)) over () * 100)||'%',10,' ') percent

   sample_time between timestamp '2013-07-20 11:00:00'
   timestamp '2013-07-20 12:00:00'

   event = 'enq: TX - allocate ITL entry'

group by
   sql_id, event

order by
   percent desc;

Once you know the SQL_ID (from the above query, you can plug it into this query to find the exact object that is experiencing the wait:

select *
from (

      count(*) as wait_count
      dba_hist_active_sess_history ash

   left join
      dba_objects obj
      obj.object_id = ash.current_obj#

      ash.sample_time between timestamp '2013-07-20 11:00:00'
      timestamp '2013-07-20 12:00:00'

   group by

   order by
      4 desc

   sql_id = 'xxxxxx'

   rownum <= 10;



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