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https://issues.apache.org/jira/browse/JENA-1023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14742544#comment-14742544
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ASF subversion and git services commented on JENA-1023:
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Commit 9ef4b05891fb6fcc96e2ee73f2e30d7b0e289bc0 in jena's branch
refs/heads/master from [~andy.seaborne]
[ https://git-wip-us.apache.org/repos/asf?p=jena.git;h=9ef4b05 ]
JENA-1023: Enable hash-based left join.
> Algebra execution join library
> ------------------------------
>
> Key: JENA-1023
> URL: https://issues.apache.org/jira/browse/JENA-1023
> Project: Apache Jena
> Issue Type: Improvement
> Components: ARQ
> Reporter: Andy Seaborne
> Assignee: Andy Seaborne
>
> This JIRA is for refactoring and adding more join algorithms into a join
> library.
> This is for joins between results from intermediate patterns, not joins that
> solve basic graph patterns.
> Normal use is a index join algorithm but it has some requirements about
> variable scope. ARQ falls back to a general join mechanism if the scoping
> requirements aren't met (this unusual).
> The general join code is not good. It should be, for example, a hash join if
> possible.
> Relation to JENA-266: There is hash-based anti-join code in
> {{org.apache.jena.sparql.engine.index}} in support of {{MINUS}}. This is not
> a proposal to combine that code into the join library. It is not immediately
> clear that code to cover all cases (inner join, left join and anti-join) at
> once is really a good idea if it leads to excessively complicated code.
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