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From sureshsubbiah <...@git.apache.org>
Subject [GitHub] incubator-trafodion pull request: fix #JIRA 1449: missing end key.
Date Thu, 27 Aug 2015 15:32:38 GMT
Github user sureshsubbiah commented on a diff in the pull request:

    https://github.com/apache/incubator-trafodion/pull/66#discussion_r38109423
  
    --- Diff: core/sql/generator/GenPreCode.cpp ---
    @@ -154,15 +154,19 @@ static NABoolean processConstHBaseKeys(Generator * generator,
       // convert built-in search key to entries with constants, if possible
       if (skey->areAllKeysConstants(TRUE))
         {
    -      ValueIdSet exePreds;
           ValueIdSet nonKeyColumnSet;
           idesc->getNonKeyColumnSet(nonKeyColumnSet);
     
    -      // seed exePreds with all predicates, key and non-key
    -      // they will be reduced by the method below
    -      skey->getKeyPredicates(exePreds);
    +      // seed keyPreds with only the full key predicate from skey
    +      ValueIdSet keyPreds = skey->getFullKeyPredicates();
    +
    +      // include executorPreds and selection predicates 
    +      // but exclude the full key predicates.
    +      ValueIdSet exePreds;
    +
           exePreds += executorPreds;
           exePreds += relExpr->getSelectionPred();
    +      exePreds.subtractSet(keyPreds);
    --- End diff --
    
    I am wondering if this is a good thing to do. There are instances where we want a predicate
to be both an executor predicate as well as a key predicate. In certain MDAM disjuncts the
key predicate guarantees that a minimal set of rows is scanned but an exe pred has to be evaluated
on the same pred again to guarantee correct results. I realize that the comment is vague without
an example or two. I can  try to find one if necessary. Also since this PreCodeGen a predicate
can be physically implemented differently based on what is available. That may also require
us to keep things in the exepred? 


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