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https://issues.apache.org/jira/browse/JENA-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13084187#comment-13084187
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Paolo Castagna commented on JENA-90:
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> I think 3 is neater.
Ok.
However, I still have a doubt.
With this algebra expression:
(slice _ 10
(distinct
(order (?p)
...)))
The optimization in JENA-89 will not trigger. Therefore there will be no (top
...)
Could we have the distinct before the order?
(slice _ 10
(order (?p)
(distinct
...)))
Or, should we do it in OpExecutor(OpSlice) checking if it sees the algebra
patter (slice ... (distinct ... (order (...)))?
> Use OpReduce instead of OpDistinct for DISTINCT + ORDER BY queries
> ------------------------------------------------------------------
>
> Key: JENA-90
> URL: https://issues.apache.org/jira/browse/JENA-90
> Project: Jena
> Issue Type: Improvement
> Components: ARQ
> Reporter: Paolo Castagna
> Priority: Trivial
> Labels: arq, optimizer, sparql
>
> ARQ's optimizer could use an OpReduce instead of OpDistinct if a query is
> DISTINCT + ORDER BY.
> OpReduce removes adjacent duplicates and it does not require a set of already
> seen bindings as the current OpDistinct implementation does.
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