Technical Blog Post
Consideration while scheduling long running BIRT reports.
Many times Application servers are restrated because of different reasons. If an application server is executing scheduled reports while the system is restarted then those reports will not re-execute automatically. To avoid that condition scheduled reports are rescheduled to run when report framework thinks that there is no activity on a report for 15 minutes. Report framework thinks that there is no activity on a report when a report SQL runs for more than 15 minutes or the report renders for more than 15 minutes. If a report SQL runs for 15 minutes then report framework thinks that the server executing the report has gonedown and reschedules the report and there is a chance that this goes in to a cycle and after every 15 to 30 minutes (30 is just an example) the report is scheduled again. When this happens the report user will get a scheduled report email every 15 to 30 minutes for the exact same report.
This 15 minutes idle time is default value which is configurable. This value is set in LOCKINTERVALINMINUTES parameter of REPORTLOCKRELEASE Crontask. Make it larger than the expected time the report will run.