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Don Burleson Blog 








Parallel query error ORA-12801

Oracle Database Tips by Donald Burleson


Question:  When running Oracle parallel query, I get a sporadic error like this:


ERROR: ORACLE execute error: ORA-12801: error signaled in parallel query server P017
ORA-01652: unable to extend temp segment by
314 in tablespace TEMP.

I understand the ORA-01652 as being caused by running out of space, but I do not understand the ORA-12801.

Answer:  Wow, P017, that's a lot of parallel query processes.  Just make sure that you have enough processors to support this load.  I've seen this ORA-12801 error pop-up intermittently for no apparent reason, usually when the server is especially active, and it's always the second message (in your case, ORA-01652).


MOSC note 184416.1 has details on diagnosing the ORA-12801 error.  It notes that the ORA-12801 is somewhat generic and that you should look for more details in your alert.log or in trace files in the USER_DUMP_DEST or BACKGROUND_DUMP_DEST
location.  You can
set event 10397 to get more details:

ORA-12801, 00000, "error signaled in parallel query server %s"

Cause: A parallel query server reached an exception condition.

Action: Check the following error message for the cause, and consult your error manual for the appropriate action.

*Comment: This error can be turned off with event 10397, in which case the server's actual error is signaled instead.

In any case, the central question is why your parallel query was performing a sort, resulting in the ORA-01652 error

OPQ generally sorts as the final step, after the paralel processes have returned the result set to the parallel query coordinator (usually P00).

The symptom solution, of course, is to increase the size of your TEMP tablespace, or better still, increase your sort_area_size.  If this job is running batch, you can do this with an alter session command, as this this case, to one gig:

alter session set sort_area_size = 1,048,576,000

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