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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-8906) Experiment with optimizing partition merging when we can prove that some sources don't overlap
Date Wed, 04 Mar 2015 16:35:04 GMT
Sylvain Lebresne created CASSANDRA-8906:
-------------------------------------------

             Summary: Experiment with optimizing partition merging when we can prove that
some sources don't overlap
                 Key: CASSANDRA-8906
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8906
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Sylvain Lebresne


When we merge a partition from two sources and it turns out that those 2 sources don't overlap
for that partition, we still end up doing one comparison by row in the first source. However,
if we can prove that the 2 sources don't overlap, for example by using the sstable min/max
clustering values that we store, we could speed this up. Note that it practice it's little
bit more hairy because we need to deal with N sources, but that's probably not too hard either.

I'll note that using the sstable min/max clustering values is not terribly precise. We could
do better if we were to push the same reasoning inside the merge iterator, by for instance
using the sstable per-partition index, which can in theory tell use things like "don't bother
comparing rows until the end of this row block". This is quite a bit more involved though
so maybe note worth the complexity.



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