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https://issues.apache.org/jira/browse/JENA-1023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14742545#comment-14742545
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Andy Seaborne commented on JENA-1023:
-------------------------------------
All operations now written and enabled.
To switch back: class {{org.apache.jena.sparql.engine.join.Join}} has two
switches, one for each of inner and leftout joins as to whether the used new
code.
For debugging, the reference query engine (which does not use this code at
all), can be run on small examples using {{--engine=ref}} to the {{arq.sparql}}
command line tool.
> 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
> Fix For: Jena 3.0.1
>
>
> 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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