Tuesday, February 10, 2009

High Performance Oracle Database Export using Data Pump

Oracle offers high performance database not only in DDL and DML. Not only this that, but also in data backup and recovery. Oracle 10g offers new export/import utilities called data dump. The biggest advance of using data dump is it can push the system’s hardware capabilities to roof to achieve performance.

Oracle Data Pump is the replacement for the original Export and Import utilities. Available starting in Oracle Database 10g, Oracle Data Pump enables very high-speed movement of data and metadata from one database to another.

The Data Pump Export and Import utilities have a similar look and feel to the original utilities, but they are much more efficient and give you greater control and management of your import and export jobs.

Unlike original export/import utilities, data pump runs as jobs primarily on the server using server processes and stores the data in database server itself avoiding network latency(Except db link).

Data pump utilities uses direct file manipulation on the directory objects which helps us to achieve the speed. Since directory object can be managed from Oracle, security can be controlled by DBA.

Sample Practical example for export using data pump (expdp)
1. Creating directory 
Data pump works on direct file manipulation on database object directory. So before invoking data pump utilities, we need to create directory object and grant required permission. See the sample below.

create directory hr_backup_dir as '/u02/dbbackup';
grant read, write on directory hr_backup_dir to scott;

2. decide on parallelism
If you the whole system resource is dedicated to database backup, then PARALLEL can be set to number of processor available in that system. If you want to assign only limited processor for backup, then set PARALLEL count accordingly. Based on the PARALLEL count, data dump will span that many number of child Oracle processes.
Parallelism also depends on the number of DUMPFILE specified in expdp. Data pump thread needs exclusive access to DUMPFILE. So if you specify PARALLEL to 8 and give only 1 DUMPFILE, then only 1 data pump process will do export and all other processes will wait for first process to finish and release the dump file. So plan for both PARALLEL and DUMPFILE parameter.

3. run expdp
Here we go

expdp hr/hrworks SCHEMAS=HR DIRECTORY= hr_backup_dir DUMPFILE=hr.thiru.10-feb-2009%U.dmp LOGFILE=hr.thiru.10-feb-2009.log PARALLEL=8 JOB_NAME=HRDataPumpByThiru

If you specify %U in DUMPFILE, data pump will automatically create required number of files (most probably number of files created will be equal to PARALLEL).

4. check log files
Once export got completed, we can check the details in hr.thiru.10-feb-2009.log file.

Interactive Mode
While data pump export operation is going, user can press ctrl + c; it will stop displaying message in screen, but it will not stop the export operation. Instead it display Export prompt which is interactive. From here user can query to see the status of export operation and also alter data pump parameters such as parallel and so on.

Database Monitoring
DBA or any other user have permission can view the status of the export operation from the database views, too. The main view to monitor the jobs is DBA_DATAPUMP_JOBS, which tells how many worker processes (column DEGREE) are working on the job. The other view that is important is DBA_DATAPUMP_SESSIONS, which when joined with the previous view and V$SESSION gives the SID of the session of the main foreground process.

select sid, serial# from v$session s, dba_datapump_sessions d where s.saddr = d.saddr;

For more information refer Oracle documentation here

Post your valuable feedback.


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Anonymous said...

Good post. I found lot of useful articles on datapump in this link.