[jira] [Updated] (ACCUMULO-2915) Avoid copying all Mutations when using a TabletServerBatchWriter

["Josh Elser (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ACCUMULO-2915?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Josh Elser updated ACCUMULO-2915:
---------------------------------
    Fix Version/s:     (was: 1.5.2)
                   1.5.3

> Avoid copying all Mutations when using a TabletServerBatchWriter
> ----------------------------------------------------------------
>
>                 Key: ACCUMULO-2915
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2915
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 1.5.0, 1.5.1, 1.6.0, 1.6.1, 1.7.0
>            Reporter: William Slacum
>            Assignee: William Slacum
>             Fix For: 1.5.3, 1.6.1, 1.7.0
>
>
> Currently in the TabletServerBatchWriter, the following behavior is exhibited:
> {code}
>     // create a copy of mutation so that after this method returns the user
>     // is free to reuse the mutation object, like calling readFields... this
>     // is important for the case where a mutation is passed from map to reduce
>     // to batch writer... the map reduce code will keep passing the same mutation
>     // object into the reduce method
>     m = new Mutation(m);
>     
>     totalMemUsed += m.estimatedMemoryUsed();
>     mutations.addMutation(table, m);
>     totalAdded++;
> {code}
> This means all data is copied twice when writing. The logic for doing this is a bit dubious, since not all clients are going to be subject to MapReduce's use of references. 
> It'd be good if we provided users with a way of signaling that there's no need to copy the mutation payload. [~elserj] suggested creating something akin to an {{ImmutableMutation}}, which help avoid some of the fears the batchwriter attempts to defend against.



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