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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Created: (CASSANDRA-789) Add configurable range sizes, paging to hadoop range queries
Date Fri, 12 Feb 2010 21:32:27 GMT
Add configurable range sizes, paging to hadoop range queries
------------------------------------------------------------

                 Key: CASSANDRA-789
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-789
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Jonathan Ellis
            Priority: Minor


For very large (billions) numbers of keys, the current hardcoded 4096 keys per InputSplit
could cause the split generator to OOM, since all splits are held in memory at once.  So we
want to make 2 changes:

 1) make the number of keys configurable*
 2) make record reader page instead of assuming it can read all rows into memory at once

Note: going back to specifying number of splits instead of number of keys is bad for two reasons.
 First, it does not work with the standard hadoop mapred.min.split.size configuration option.
 Second, it means we have no way of measuring progress in the record reader, since we have
no idea how many keys are in the split.  If we specify number of keys, then even if we page
we know (to within a small margin of error) how many keys to expect, even if we page.

See CASSANDRA-775, CASSANDRA-342 for background.

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