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https://issues.apache.org/jira/browse/LENS-1452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16353401#comment-16353401
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Hudson commented on LENS-1452:
------------------------------
FAILURE: Integrated in Jenkins build Lens-Commit #1458 (See
[https://builds.apache.org/job/Lens-Commit/1458/])
LENS-1452: Optimize Time Union candidate Algorithm (rajatgupta59: rev
6dca44661bf604ca1436c6cd1d3998405d0333a4)
* (edit)
lens-cube/src/main/java/org/apache/lens/cube/parse/CandidateCoveringSetsResolver.java
> Optimize Time Union candidate Algorithm
> ---------------------------------------
>
> Key: LENS-1452
> URL: https://issues.apache.org/jira/browse/LENS-1452
> Project: Apache Lens
> Issue Type: Task
> Components: cube
> Reporter: Rajat Khandelwal
> Assignee: Rajat Khandelwal
> Priority: Major
> Attachments: LENS-1452.01.patch
>
>
> Current algorithm:
> * Create bitmap (equivalent to powerset)
> * from the powerset, add sets which can complete all time ranges as candidates
> * Prune sets which are contained in other sets
> Proposed change:
> The following recursion implemented iteratively:
> {code}
> (ignoring cubeql for clarity)
> getCombinations(candidates) = getCombinationsRecursive(emptyList(),
> candidates)
> getCombinationsRecursive(incompleteCombinations: List<List<Candidate>>,
> candidates: List<Candidate>) =
> head, tail = head and tail of linked List candidates
> add head to all elements of incompleteCombinations.
> add {{ [head] }} as one incompleteCombination.
> complete = remove now complete combinations from incompleteCombinations
> return {{complete ++
> getCombinationsTailRecursive(incompleteCombinations+[head], tail)}}
> {code}
> The improvement is, that redundant union candidates like {a,b,c} won't be
> generated if {a,b} is already covering time ranges. This will only generate
> minimal sets that cover time ranges. So the memory footprint isn't O( 2^n )
> anymore.
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