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Date: Wed, 8 Apr 2009 10:58:13 -0700 (PDT)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: cassandra-commits@incubator.apache.org
Subject: [jira] Commented: (CASSANDRA-51)  Memory footprint for memtable
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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 ] 

Jonathan Ellis commented on CASSANDRA-51:
-----------------------------------------

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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