DBMS_Scheduler chains are a joy to use, until they stop being a joy and start being a real pain.
I modified the logic of a process, dropping one stored procedure and replacing it with another (instead of writing out a list of files to a control file so that a cron job can scp them to a set of other servers, we’re now executing scp as a DBMS_Scheduler executable-type job).
Calling the new procedure instead of the old one required dropping the obsolete DBMS_Scheduler program, the chain step, and the associated rules, and creating a new program, step and rules.
The old rules, step and program were dropped, and the new program and step were created.
However when creating the first of the new rules the following error message was raised:
chain_name => 'EXPORT',
condition => 'STP_EXP_SEND_FILES_TO_PR SUCCEEDED',
action => 'START STP_RM_OLD_PROBE_FILES',
rule_name => 'START_RM_OLD_PROBE_FILES'
ORA-24172: rule set NCBI_ETL.SCHED_RULESET$4 has errors
ORA-06512: at "SYS.DBMS_ISCHED", line 1286
ORA-06512: at "SYS.DBMS_SCHEDULER", line 1257
ORA-06512: at line 2
24172. 00000 - "rule set %s.%s has errors"
*Cause: The rule references variables not in the evaluation context.
*Action: Modify the rule condition to remove illegal reference.
The error is another of those where the majority of Google hits are dumb listings of the error code and message, and the “cause” and “action”.
The syntax and names in the call to DBMS_Scheduler.Define_Chain_Rule were all validated.
I exported the rule set associated with the chain:
This told me the name of the evaluation context, which I then exported with:
On checking the evaluation context I found that the newly-added chain step was present:
vt(10) := sys.re$variable_type('"STP_EXP_SEND_FILES_TO_PR"','sys.scheduler$_job_step_type','dbms_scheduler.get_job_step_cf',NULL);
I flirted with the idea of dropping the chain entirely, after exporting the chain and steps with:
… and the rules (why are they not included in the chain definition?) with:
select 'exec DBMS_SCHEDULER.DEFINE_CHAIN_RULE ('''||chain_name||''','''||condition||''','''||action||''','''||rule_name||''','''||comments||''');'
where chain_name = 'EXPORT';
However, when I exported the rule set I noticed that there was still a rule defined with the name of the step I had previously dropped — it was the “what to do if anything fails” rule, and listed all the steps of the chain except the one that sends the chain failure email.
I dropped and created that rule with reference to failure of the new rule instead of the old one, and the new replacement rule that had previously failed now created correctly.
What I Learned
It appears that a chain step can be dropped in 10.2.0.4 even if it is referenced by a rule, but this may leave an “orphan” rule that will cause an ORA-24172 to be raised when rules are defined later on. Well, there may be other or more complete explanations, but the error that is raised may not be complaining about the rule you are trying to create — there may be another at fault.