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https://issues.apache.org/jira/browse/CASSANDRA-51?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12697123#action_12697123
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Jonathan Ellis commented on CASSANDRA-51:
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Oops, I was only looking at EBM.getColumns, not EBM.get which also uses the map.
> Memory footprint for memtable
> ------------------------------
>
> Key: CASSANDRA-51
> URL: https://issues.apache.org/jira/browse/CASSANDRA-51
> Project: Cassandra
> Issue Type: Improvement
> Environment: all
> Reporter: Sandeep Tata
>
> The implementation of EfficientBidiMap(EBM) today stores the column in two
> place, a map and a sorted set. Both data structures store exactly the same
> values.
> I assume we're storing this twice so that the map can give us O(1) reads
> while the sortedset is important for efficient flush. Is this tradeoff
> important ? Do we want to store the data twice to get O(1) reads over
> O(log(n)) reads from sortedset? Is the sortedset implementation broken?
> Perhaps we should consider a configuration option that turns off the map --
> write performance will be slightly improved, read performance will be
> somewhat worse, and the memory footprint will probably be about half.
> Certainly sounds like a good alternative tradeoff.
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