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

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-1337?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13784290#comment-13784290 ] 

Jonathan Ellis commented on CASSANDRA-1337:
-------------------------------------------

Pushed some super minor cleanup to https://github.com/jbellis/cassandra/commits/1337.

Question left in my mind is, do we want to shoot for exactly enough concurrent requests, on average?  Would imply that half the time we need to do an extra round.  ISTM we probably want to give ourselves a margin of error.

> 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: Tyler Hobbs
>            Priority: Minor
>             Fix For: 2.1
>
>         Attachments: 0001-Concurrent-range-and-2ary-index-subqueries.patch, 1137-bugfix.patch, 1337.patch, 1337-v4.patch, ASF.LICENSE.NOT.GRANTED--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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