[jira] Issue Comment Edited: (CASSANDRA-51) Memory footprint for memtable

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-51?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12697928#action_12697928 ] 

Jonathan Ellis edited comment on CASSANDRA-51 at 4/10/09 12:13 PM:
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Right.  I think that NameSortColumnFamily and TimeSortColumnFamily might not be a bad specialization to make.  For us at least we will use a lot more name sorted so gaining efficiency there is worth a little effort.  But this should wait until we have a performance test.


      was (Author: jbellis):
    Right.  I think that NameSortColumn and TimeSortColumn might not be a bad specialization to make.  For us at least we will use a lot more name sorted so gaining efficiency there is worth a little effort.  But this should wait until we have a performance test.

  
>  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
>            Assignee: Eric Evans
>             Fix For: 0.3
>
>
> 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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