[jira] [Updated] (CASSANDRA-5506) Reduce memory consumption of IndexSummary

["Ryan McGuire (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-5506?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ryan McGuire updated CASSANDRA-5506:
------------------------------------

    Labels: qa-resolved  (was: )

> Reduce memory consumption of IndexSummary
> -----------------------------------------
>
>                 Key: CASSANDRA-5506
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5506
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Nick Puz
>            Assignee: Jonathan Ellis
>              Labels: qa-resolved
>             Fix For: 1.2.5
>
>
> I am evaluating cassandra for a use case with many tiny rows which would result in a node with 1-3TB of storage having billions of rows. Before loading that much data I am hitting GC issues and when looking at the heap dump I noticed that 70+% of the memory was used by IndexSummaries. 
> The two major issues seem to be:
> 1) that the positions are stored as an ArrayList<Long> which results in each position taking 24 bytes (class + flags + 8 byte long). This might make sense when the file is initially written but once it has been serialized it would be a lot more memory efficient to just have an long[] (really a int[] would be fine unless 2GB sstables are allowed).
> 2) The DecoratedKey for a byte[16] key takes 195 bytes -- this is for the overhead of the ByteBuffer in the key and overhead in the token.
> To somewhat "work around" the problem I have increased index_sample but will this many rows that didn't really help starts to have diminishing returns. 
> NOTE: This heap dump was from linux with a 64bit oracle vm. 



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