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https://issues.apache.org/jira/browse/ACCUMULO-2915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14033162#comment-14033162
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William Slacum commented on ACCUMULO-2915:
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[~kturner] serves me right for not digging deeper in there.
> 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
> Fix For: 1.5.2, 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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