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https://issues.apache.org/jira/browse/SOLR-9684?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15792043#comment-15792043
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Joel Bernstein commented on SOLR-9684:
--------------------------------------
Ok, then let's go with *priority* as the name for this function.
About the *merge* function. The merge function is shorthand for "mergeSort".
It's designed to merge two streams sorted on the same keys and maintain the
sort order. Originally the idea was that the /export handler was a giant
sorting engine, and merge was a way to efficiently merge the sorted streams.
The priority function behaves more like the SQL UNIONALL with priority. But
it's different in that priority is only picks one stream to iterate on each
open/close. This design allows it to iterate the high priority topic until it's
empty, and only then iterate through the lower priority topic.
Eventually we'll need to implement both a UnionStream and UnionAllStream as
well.
> Add schedule Streaming Expression
> ---------------------------------
>
> Key: SOLR-9684
> URL: https://issues.apache.org/jira/browse/SOLR-9684
> Project: Solr
> Issue Type: New Feature
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Joel Bernstein
> Assignee: Joel Bernstein
> Fix For: master (7.0), 6.4
>
> Attachments: SOLR-9684.patch, SOLR-9684.patch, SOLR-9684.patch
>
>
> SOLR-9559 adds a general purpose *parallel task executor* for streaming
> expressions. The executor() function executes a stream of tasks and doesn't
> have any concept of task priority.
> The scheduler() function wraps two streams, a high priority stream and a low
> priority stream. The scheduler function emits tuples from the high priority
> stream first, and then the low priority stream.
> The executor() function can then wrap the scheduler function to see tasks in
> priority order.
> Pseudo syntax:
> {code}
> daemon(executor(schedule(topic(tasks, q="priority:high"), topic(tasks,
> q="priority:low"))))
> {code}
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