event 10384

event 10384 level 16384: force parallel query runs as serial. How to Force that a Parallel Query Runs in Serial with the Parallel Execution Plan (Doc ID 1114405.1)

[oracle@oracle]$ oerr ora 10384
10384, 00000, "parallel dataflow scheduler tracing"
// *Cause:
// *Action:   set this event only under the supervision of Oracle development
// *Comment:  trace level is a bitfield (see kkrp.h)

Test case (run on 11.2.0.3):

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doc   create test data # create table t as select * from dba_objects;   doc   set statistics_level=all and run parallel query #   alter session set statistics_level=all; select /*+ parallel(t)*/count(*) from t; select * from table(dbms_xplan.display_cursor( format=> 'allstats all'));   doc   purge cursor #   col address    new_v address col hash_value new_v hash_value select address, hash_value from v$sql where sql_id='apmsk02t1z90x'; exec sys.dbms_shared_pool.purge( '&address.,&hash_value.', 'c')   doc   set event 10384 level 16384, _px_trace=all and run query #   alter session set events '10384 level 16384'; alter session set "_px_trace"=all;   select /*+ parallel(t)*/count(*) from t; select * from table(dbms_xplan.display_cursor( format=> 'allstats all')); alter session set events '10384 off';

Row source execution statistics of first execution. Default degree 16, starts for 5th line is 16.

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----------------------------------------------------------------------------------------------------------------------------------------------------------- | Id  | Operation              | Name     | Starts | E-Rows | Cost (%CPU)| E-Time   |    TQ  |IN-OUT| PQ Distrib | A-Rows |   A-Time   | Buffers | Reads  | ----------------------------------------------------------------------------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT       |          |      1 |        |     4 (100)|          |        |      |            |      1 |00:00:00.59 |       5 |      0 | |   1 |  SORT AGGREGATE        |          |      1 |      1 |            |          |        |      |            |      1 |00:00:00.59 |       5 |      0 | |   2 |   PX COORDINATOR       |          |      1 |        |            |          |        |      |            |     16 |00:00:00.59 |       5 |      0 | |   3 |    PX SEND QC (RANDOM) | :TQ10000 |      0 |      1 |            |          |  Q1,00 | P->S | QC (RAND)  |      0 |00:00:00.01 |       0 |      0 | |   4 |     SORT AGGREGATE     |          |     16 |      1 |            |          |  Q1,00 | PCWP |            |     16 |00:00:01.16 |     567 |    189 | |   5 |      PX BLOCK ITERATOR |          |     16 |  12736 |     4   (0)| 00:00:01 |  Q1,00 | PCWC |            |  14275 |00:00:01.16 |     567 |    189 | |*  6 |       TABLE ACCESS FULL| T        |    189 |  12736 |     4   (0)| 00:00:01 |  Q1,00 | PCWP |            |  14275 |00:00:01.14 |     567 |    189 | -----------------------------------------------------------------------------------------------------------------------------------------------------------

Row source execution statistics of second execution. Starts for 5th line is 1. Parallel plan executed serially.

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----------------------------------------------------------------------------------------------------------------------------------------------------------- | Id  | Operation              | Name     | Starts | E-Rows | Cost (%CPU)| E-Time   |    TQ  |IN-OUT| PQ Distrib | A-Rows |   A-Time   | Buffers | Reads  | ----------------------------------------------------------------------------------------------------------------------------------------------------------- |   0 | SELECT STATEMENT       |          |      1 |        |     4 (100)|          |        |      |            |      1 |00:00:00.02 |     194 |     63 | |   1 |  SORT AGGREGATE        |          |      1 |      1 |            |          |        |      |            |      1 |00:00:00.02 |     194 |     63 | |   2 |   PX COORDINATOR       |          |      1 |        |            |          |        |      |            |      1 |00:00:00.02 |     194 |     63 | |   3 |    PX SEND QC (RANDOM) | :TQ10000 |      1 |      1 |            |          |  Q1,00 | P->S | QC (RAND)  |      1 |00:00:00.02 |     194 |     63 | |   4 |     SORT AGGREGATE     |          |      1 |      1 |            |          |  Q1,00 | PCWP |            |      1 |00:00:00.02 |     194 |     63 | |   5 |      PX BLOCK ITERATOR |          |      1 |  12736 |     4   (0)| 00:00:01 |  Q1,00 | PCWC |            |  14275 |00:00:00.02 |     194 |     63 | |*  6 |       TABLE ACCESS FULL| T        |      1 |  12736 |     4   (0)| 00:00:01 |  Q1,00 | PCWP |            |  14275 |00:00:00.02 |     194 |     63 | -----------------------------------------------------------------------------------------------------------------------------------------------------------

Trace file with event 10384 set contains a line:

Parallelism disabled at runtime because forced serial by event 10384