Question

I have a series of scripts running in parallel as a nohup on an AIX server hosting oracle 10g. These scripts are written by somebody else and are meant to be executed concurrently. All the scripts are performing updates on a table. I am getting the error,

ORA-00060: deadlock detected while
waiting for resource

As I googled for this, I found,
http://www.dba-oracle.com/t_deadly_perpetual_embrace_locks.htm

Even though the scripts are performing updation on the same table concurrently, they are performing updates on different records of the table determined by the WHERE clause with no overlaps of records between them.

So would this have caused the error?.

Will this error happen regardless of where the updates are performed on a table?.

Should I avoid concurrent updates on a table at all times?.

Strangely I also found on the nohup.out log,
PL/SQL successfully completed after the above quoted error.

Does this mean that oracle has recovered from the deadlock and completed the updates successfully or Should I rerun those scripts serially?

Answer 1

You can get deadlocks on more than just row locks, e.g. see this. The scripts may be competing for other resources, such as index blocks.

I’ve gotten around this in the past by engineering the parallelism in such a way that different instances are working on portions of the workload that are less likely to affect blocks that are close to each other; for example, for an update of a large table, instead of setting up the parallel slaves using something like MOD(n,10), I’d use TRUNC(n/10) which mean that each slave worked on a contiguous set of data.

There are, of course, much better ways of splitting up a job for parallelism, e.g. DBMS_PARALLEL_EXECUTE.

Not sure why you’re getting “PL/SQL successfully completed”, perhaps your scripts are handling the exception?