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How to Make PL/SQL Updates Restartable

Oracle Database Tips by Burleson Consulting

June 21, 2015

Question:  I want my PL/SQL program to be restartable, such that if there is an abort from a non-zero return code, the PL/SQL program will restart from the last commit checkpoint. 

What is the best way to make a PL/SQL batch update job restartable?

Answer:  Obviously, the best way to make PL/SQL DML jobs restartable is to never use a commit, and re-run the whole job. 

Sadly, the exact PL/SQL to make a PL/SQL update/insert/delete is difficult because there is no preset order for DML to inspect and change all rows within a table.

You cannot save the current cursor where the updated aborted, so twiddling a cursor is not a solution, and you must alter your code to ignore previous updates and restart.

 Also change your dbms_scheduler to mark your job as restartable.

To make a scheduled PL/SQL job restartable with dbms_scheduler, set the operation flag to retry_run. This says that the job is being retried because the previous run resulted in an error and RESTARTABLE is set to TRUE.

This will roll back all database changes and the PL/SQL is automatically restartable.

 However, in cases where it is not feasible to wait many hours for a zillion rows update to rollback and re-start the batch job, more creative restart methods are desired.

 Again, The best solution to make a PL/SQL DML job re-startable is to never place intermediate commitstatements and let the job run, where it will either abort and fully rollback else of commit at end of job (EOJ) time.   When a job is too long to run with no intermediate commits (e.g. a 12 hour night update job), then there are several ways to make PL/SQL update/insert/delete restartable:

  1.  Have a last_updated_flag column and have your PL/SQL test to see which rows have already been changed.
  2. If the DML changes can be identified programmatically, simply re-run the PL/SQL update, bypassing row values that have already been updated.
  3. There is a dbms_xmlgen.restartQuery(ctx IN ctxHandle) package.  The restartquery procedure will restarts a read-only query and generate the XML from the first row. It can be used to start executing the query again, without having to create a new context.  
  4. For query-only PL/SQL (only for  super-large PL/SQL reports that write to flat files), you can make them restartable by using utl_file to read the last report row written and then spin the code until you reach that point.  However, most PL/SQL reports are sorted, so the entire query must be re-run to find the point where the code aborted.

In sum, making PL/SQL is highly dependent on the nature of your specific PL/SQL code.   

If you want to rent a 3rd party programmer to make your PL/SQL program restartable, call 800-766-1884.

 
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