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Posted to dev@jena.apache.org by "Stephen Allen (Commented) (JIRA)" <ji...@apache.org> on 2011/11/24 01:16:40 UTC
[jira] [Commented] (JENA-119) Eliminate memory bounds during query
execution
[ https://issues.apache.org/jira/browse/JENA-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13156422#comment-13156422 ]
Stephen Allen commented on JENA-119:
------------------------------------
Completed QueryIterDistinct. It streams until it passed the threshold for the first time, at which point it consumes the entire input iterator before returning further bindings.
Committed in revision 1205673.
> Eliminate memory bounds during query execution
> ----------------------------------------------
>
> Key: JENA-119
> URL: https://issues.apache.org/jira/browse/JENA-119
> Project: Jena
> Issue Type: New Feature
> Components: ARQ
> Reporter: Stephen Allen
> Assignee: Stephen Allen
> Attachments: JENA-119-r1177090-Fuseki-Construct.patch, JENA-119-r1177452-ARQ-Construct.patch
>
>
> It would be nice to eliminate all memory bounds on queries. Similar to JENA-44, it would involve modifying all of the QueryIterator objects that maintain unbounded collections of Bindings.
> The ones I've identified (let me know if I've missed any):
> + QueryIterSort
> Complete!
> + QueryIterGroup
> Probably one of the more complicated implementations. I think it can be done with a DistinctDataBag.
> + QueryIterDistinct
> Can be implemented trivially using DistinctDataBag, but would lose streaming capability. We could do streaming just until the first spill, which would be a little more difficult but not bad. If we wanted streaming even after spilling, then we would need an on-disk hashtable or b-tree (which could get expensive for maybe limited benefit, do you really need streaming after 10,000 results?).
> + QueryIteratorCopy
> Only appears to be used QueryIterService. Simple implementation using DefaultDataBag.
> + QueryIteratorCaching
> Does not match DataBag's assumption of completing all writes before iterating. But it isn't used anywhere, so maybe we remove it?
> + QueryIterDiff
> + QueryIterMinus
> Both of these materialize the RHS into a collection. Can be implemented with DefaultDataBag. As an aside, is this necessary to do for all queries? What if the RHS is cheap (i.e. a single TriplePattern)?
> + QueryIterJoin
> + QueryIterLeftJoin
> Both materialize RHS. Are they used anywhere? I was under the impression that ARQ only considered left-deep plans with indexed joins on the RHS TriplePatterns.
> + SubQueries
> I'm not sure how this is handled. Are these materialized somewhere?
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