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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-10378) Make skipping more efficient
Date Sat, 19 Sep 2015 15:51:04 GMT
Benedict created CASSANDRA-10378:
------------------------------------

             Summary: Make skipping more efficient
                 Key: CASSANDRA-10378
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10378
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Benedict
            Assignee: Benedict
             Fix For: 3.x


Following on from the impact of CASSANDRA-10322, we can improve the efficiency of our calls
to skipping methods. CASSANDRA-10326 is showing our performance to be in-and-around the same
ballpark except for seeks into the middle of a large partition, which suggests (possibly)
that the higher density of data we're storing may simply be resulting in a more significant
CPU burden as we have more data to skip over (and since CASSANDRA-10322 improves performance
here really dramatically, further improvements are likely to be of similar benefit).

I propose doing our best to flatten the skipping of macro data items into as few skip invocations
as necessary. One way of doing this would be to introduce a special {{skipUnsignedVInts(int)}}
method, that can efficiently skip a number of unsigned vints. Almost the entire body of a
cell and row consist of vints now, each data component with their own special {{skipX}} method
that invokes {{readUnsignedVint}}. This would permit more efficient despatch.

We could also potentially avoid the construction of a new {{Columns}} instance for each row
skip, since all we need is an iterator over the columns, and share the temporary space used
for storing them, which should further reduce the GC burden for skipping many rows.



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