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Parallel slows down job - why so ?

JhilAug 2 2015 — edited Aug 7 2015

Hi all;

I have tested  a schema export , size around 2gb  ( with parallal  Vs without parallel)

no indexes , no constriants  .. ( schema contains only dummy data)

Option1 :

$ expdp system/manager dumpfile=file01.dmp, file02.dmp, file03.dmp, file04.dmp  logfile=test1.log schemas=maya parallel=3 directory=dp


  Export: Release 11.2.0.1.0 - Production on Sun Aug 2 14:06:56 2015

..

...

Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_08 is:

  /u01/datapump/file01.dmp

  /u01/datapump/file02.dmp

  /u01/datapump/file03.dmp

  /u01/datapump/file04.dmp

Job "SYSTEM"."SYS_EXPORT_SCHEMA_08" successfully completed at 14:16:33

Process took time  almost 10 minutes  ( when parallel =3)

Option 2 :

$ expdp system/manager dumpfile=file1.dmp schemas=maya directory=dp  logfile=test2.log

Export: Release 11.2.0.1.0 - Production on Sun Aug 2 14:18:46 2015

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

Starting "SYSTEM"."SYS_EXPORT_SCHEMA_08":  system/******** dumpfile=file1.dmp schemas=maya directory=dp logfile=test2.log

Estimate in progress using BLOCKS method...

Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA

Total estimation using BLOCKS method: 2.125 GB

Processing object type SCHEMA_EXPORT/USER

Processing object type SCHEMA_EXPORT/ROLE_GRANT

Processing object type SCHEMA_EXPORT/DEFAULT_ROLE

Processing object type SCHEMA_EXPORT/TABLESPACE_QUOTA

Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA

Processing object type SCHEMA_EXPORT/TABLE/TABLE

Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS

. . exported "MAYA"."TABB1"                              899.6 MB 48000000 rows

. . exported "MAYA"."TABB2"                              899.6 MB 48000000 rows

Master table "SYSTEM"."SYS_EXPORT_SCHEMA_08" successfully loaded/unloaded

******************************************************************************

Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_08 is:

  /u01/datapump/file1.dmp

Job "SYSTEM"."SYS_EXPORT_SCHEMA_08" successfully completed at 14:21:23

Result :

Default     :   takes  157 seconds  to complete the job ( without parallel)

parallel=3 :  takes  577 seconds  to complete the job ( parallel=3)

please suggest , i am getting confused with parallel options.

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Locked on Sep 4 2015
Added on Aug 2 2015
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