[jira] [Reopened] (CASSANDRA-1337) parallelize fetching rows for low-cardinality indexes

["Sylvain Lebresne (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-1337?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sylvain Lebresne reopened CASSANDRA-1337:
-----------------------------------------


This broke range slices as shown by the following test added to dtests: https://github.com/riptano/cassandra-dtest/commit/c83fabf390c3e3fb10708a81b8220f65bacd41bc

The underlying reason is that for that test, in StorageProxy.getRangeSlice(), concurrencyFactor is 3 (there is 3 restricted ranges), but for one of the range the local path is taken, and so scanHandlers.size() is always < concurrencyFactor and so we don't wait the other node answer.
                
> 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
>            Priority: Minor
>             Fix For: 1.2
>
>         Attachments: 0001-CASSANDRA-1337-scan-concurrently-depending-on-num-rows.txt, 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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