[jira] [Updated] (LENS-1452) Optimize Time Union candidate Algorithm

["Rajat Khandelwal (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LENS-1452?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Rajat Khandelwal updated LENS-1452:
-----------------------------------
    Attachment: LENS-1452.01.patch

> 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
>         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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