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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-51) Memory footprint for memtable
Date Thu, 09 Apr 2009 14:43:13 GMT


Jonathan Ellis commented on CASSANDRA-51:

Oh, that's right; time-ordered CF's are pretty much a deal breaker.  No doubt that's why the
two-collection approach was adopted in the first place.

One last idea: see if ConcurrentHashMap(8, 0.8, 1) saves a noticable amount of memory over

>  Memory footprint for memtable
> ------------------------------
>                 Key: CASSANDRA-51
>                 URL:
>             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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