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From "David Alves (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1337) parallelize fetching rows for low-cardinality indexes
Date Sat, 09 Jun 2012 18:05:43 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1337?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13292395#comment-13292395
] 

David Alves commented on CASSANDRA-1337:
----------------------------------------

couple of questions:

- If i got the logic right the point is that we keep creating async handlers until we exceed
concurrency factor, at which time we block and wait for the replies, clear the handlers and
start again. Can't we reach a state where we have handlers to which we haven't called get()
(because they have not exceeded concurrecy factor?).
- On another matter what would be the best strategy to test this both for correctness and
speed?


                
> 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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