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https://issues.apache.org/jira/browse/SLING-5387?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15986326#comment-15986326
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Carsten Ziegeler commented on SLING-5387:
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I'm not sure if we need to go there. These jobs are scheduled. So if job A is
currently running on an instance, and while it is running the topology changes,
then job A will not be immediately scheduled on a different instance. First of
all, the distribution algorithm must calculate a different result than
previously which might or might not be the case. But more important, these jobs
are scheduled. So usually, the schedule is defined in a way that the next run
of A is after the previous run of A is finished. And if the schedule is in such
a way that there are multiple jobs of A potentially running in parallel, then
I think we're fine as well.
Of course, there is the slight chance that the topology changes exactly at the
point of an activation of a schedule and then the job runs in parallel. But I
think this chance is pretty low.
> Provide support for running singleton jobs on non leader cluster nodes also
> ---------------------------------------------------------------------------
>
> Key: SLING-5387
> URL: https://issues.apache.org/jira/browse/SLING-5387
> Project: Sling
> Issue Type: Improvement
> Components: Commons
> Reporter: Chetan Mehrotra
> Assignee: Carsten Ziegeler
> Fix For: Commons Scheduler 2.5.4
>
>
> With SLING-2979 support for running singleton jobs on specific instance was
> provided. In most cases we want to run a job as singleton and not want to
> "pin" it to specific nodes. For this {{scheduler.runOn}} needs to be set to
> {{SINGLE}}.
> However per [current
> implementation|https://github.com/apache/sling/blob/org.apache.sling.commons.scheduler-2.4.14/src/main/java/org/apache/sling/commons/scheduler/impl/QuartzJobExecutor.java#L64]
> {{SINGLE}} is treated as {{LEADER}}. This effectively causes *all singleton*
> jobs to get executed on leader only thus putting extra load.
> For better utilization of cluster resources it should be possible to
> distribute such singleton jobs on other cluster nodes and still ensure that
> singleton contract is honoured!
> We would like to make use of this feature to ensure Oak AsyncIndexTask to run
> on different cluster nodes (OAK-2749)
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