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https://issues.apache.org/jira/browse/CASSANDRA-1337?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sylvain Lebresne reopened CASSANDRA-1337:
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I'm sorry but I still don't see how that handle correctly 2ndary indexes (in
the non-CQL3 case, fine for putting CQL3 to a following ticket if you prefer).
Also, the parallelHandlers integer of the "fix" doesn't really work. Suppose
you have a concurrencyFactor of 2 but > 2 ranges. If the first range happens to
be a local range, you'll decrement parallelHandlers and so the following
queries we be done serially, while they should be done 2 by 2 in parallel.
Besides, why is the local case a special case in the first place? It feels like
if we're parallelizing queries, there is no reason not to parallelize the local
path too.
> parallelize fetching rows for low-cardinality indexes
> -----------------------------------------------------
>
> Key: CASSANDRA-1337
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1337
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Jonathan Ellis
> Assignee: David Alves
> Fix For: 1.2
>
> Attachments:
> 0001-CASSANDRA-1337-scan-concurrently-depending-on-num-rows.txt,
> 1137-bugfix.patch, CASSANDRA-1337.patch
>
> Original Estimate: 8h
> Remaining Estimate: 8h
>
> currently, we read the indexed rows from the first node (in partitioner
> order); if that does not have enough matching rows, we read the rows from the
> next, and so forth.
> we should use the statistics fom CASSANDRA-1155 to query multiple nodes in
> parallel, such that we have a high chance of getting enough rows w/o having
> to do another round of queries (but, if our estimate is incorrect, we do need
> to loop and do more rounds until we have enough data or we have fetched from
> each node).
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