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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-5506) Reduce memory consumption of IndexSummary
Date Mon, 22 Apr 2013 18:01:20 GMT

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

Jonathan Ellis updated CASSANDRA-5506:
--------------------------------------

             Priority: Minor  (was: Major)
    Affects Version/s:     (was: 1.2.3)
    
> 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
>            Priority: Minor
>
> 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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