Specifies the maximum number of processes of active execution operating on behalf of the export job. This execution set consists of a combination of worker processes and parallel I/O server processes. The master control process and worker processes acting as query coordinators in parallel query operations do not count toward this total.
This parameter enables you to make trade-offs between resource consumption and elapsed time.
Syntax and Description
The value you specify for
integer should be less than, or equal to, the number of files in the dump file set (or you should specify substitution variables in the dump file specifications). Because each active worker process or I/O server process writes exclusively to one file at a time, an insufficient number of files can have adverse effects. Some of the worker processes will be idle while waiting for files, thereby degrading the overall performance of the job. More importantly, if any member of a cooperating group of parallel I/O server processes cannot obtain a file for output, then the export operation will be stopped with an
ORA-39095 error. Both situations can be corrected by attaching to the job using the Data Pump Export utility, adding more files using the
ADD_FILE command while in interactive mode, and in the case of a stopped job, restarting the job.
To increase or decrease the value of
PARALLEL during job execution, use interactive-command mode. Decreasing parallelism does not result in fewer worker processes associated with the job; it decreases the number of worker processes that will be executing at any given time. Also, any ongoing work must reach an orderly completion point before the decrease takes effect. Therefore, it may take a while to see any effect from decreasing the value. Idle workers are not deleted until the job exits.
Increasing the parallelism takes effect immediately if there is work that can be performed in parallel.
Using PARALLEL During An Export In An Oracle RAC Environment
In an Oracle Real Application Clusters (Oracle RAC) environment, if an export operation has
PARALLEL=1, then all Data Pump processes reside on the instance where the job is started. Therefore, the directory object can point to local storage for that instance.
If the export operation has
PARALLEL set to a value greater than 1, then Data Pump processes can reside on instances other than the one where the job was started. Therefore, the directory object must point to shared storage that is accessible by all instances of the Oracle RAC.
This parameter is valid only in the Enterprise Edition of Oracle Database 11g or later.
To export a table or table partition in parallel (using PQ slaves), you must have the
The following is an example of using the
> expdp hr DIRECTORY=dpump_dir1 LOGFILE=parallel_export.log JOB_NAME=par4_job DUMPFILE=par_exp%u.dmp PARALLEL=4
This results in a schema-mode export (the default) of the
hr schema in which up to four files could be created in the path pointed to by the directory object,