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Overview
Comment:Simplify and add invariants to the WhereLoop merging logic inside of whereLoopInsert().
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SHA1:8f27f35f288434b9e7bc503c608f1e2b590ade4d
User & Date: drh 2013-06-19 12:34:13
Context
2013-06-19
13:32
Fix a harmless uninitialized variable warning. check-in: 9d3ef3bd user: drh tags: nextgen-query-plan-exp
12:34
Simplify and add invariants to the WhereLoop merging logic inside of whereLoopInsert(). check-in: 8f27f35f user: drh tags: nextgen-query-plan-exp
03:27
Fix compiler warnings. Fix a harmless off-by-one error in the solver. check-in: 10021941 user: drh tags: nextgen-query-plan-exp
Changes
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Changes to src/where.c.

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    return SQLITE_OK;
  }

  /* Search for an existing WhereLoop to overwrite, or which takes
  ** priority over pTemplate.
  */
  for(ppPrev=&pWInfo->pLoops, p=*ppPrev; p; ppPrev=&p->pNextLoop, p=*ppPrev){
    if( p->iTab!=pTemplate->iTab || p->iSortIdx!=pTemplate->iSortIdx ) continue;
















    if( (p->prereq & pTemplate->prereq)==p->prereq
     && p->rSetup<=pTemplate->rSetup
     && p->rRun<=pTemplate->rRun
    ){
      /* This branch taken when p is equal or better than pTemplate in 
      ** all of (1) dependences (2) setup-cost, and (3) run-cost. */
      testcase( p->rRun==pTemplate->rRun );
      if( p->nLTerm<pTemplate->nLTerm
       && (p->wsFlags & WHERE_INDEXED)!=0
       && (pTemplate->wsFlags & WHERE_INDEXED)!=0
       && p->u.btree.pIndex==pTemplate->u.btree.pIndex
       && p->prereq==pTemplate->prereq
      ){
        /* Overwrite an existing WhereLoop with an similar one that uses
        ** more terms of the index */
        pNext = p->pNextLoop;
        break;
      }else if( p->nOut>pTemplate->nOut
       && p->rSetup==pTemplate->rSetup
       && p->rRun==pTemplate->rRun
      ){
        /* Overwrite an existing WhereLoop with the same cost but more
        ** outputs */
        pNext = p->pNextLoop;
        break;
      }else{
        /* pTemplate is not helpful.
        ** Return without changing or adding anything */
        goto whereLoopInsert_noop;
      }
    }
    testcase( (p->prereq & pTemplate->prereq)==p->prereq
              && p->rSetup<=pTemplate->rSetup
              && p->rRun==pTemplate->rRun+1 );
    if( (p->prereq & pTemplate->prereq)==pTemplate->prereq
     && p->rSetup>=pTemplate->rSetup
     && p->rRun>=pTemplate->rRun

    ){
      /* Overwrite an existing WhereLoop with a better one: one that is
      ** better at one of (1) dependences, (2) setup-cost, or (3) run-cost
      ** and is no worse in any of those categories. */
      testcase( p->rSetup==pTemplate->rSetup );
      testcase( p->rRun==pTemplate->rRun );
      pNext = p->pNextLoop;
      break;
    }
    testcase( (p->prereq & pTemplate->prereq)==pTemplate->prereq
              && p->rSetup>=pTemplate->rSetup
              && p->rRun==pTemplate->rRun-1 );
  }

  /* If we reach this point it means that either p[] should be overwritten
  ** with pTemplate[] if p[] exists, or if p==NULL then allocate a new
  ** WhereLoop and insert it.
  */
#if WHERETRACE_ENABLED







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    return SQLITE_OK;
  }

  /* Search for an existing WhereLoop to overwrite, or which takes
  ** priority over pTemplate.
  */
  for(ppPrev=&pWInfo->pLoops, p=*ppPrev; p; ppPrev=&p->pNextLoop, p=*ppPrev){
    if( p->iTab!=pTemplate->iTab || p->iSortIdx!=pTemplate->iSortIdx ){
      /* If either the iTab or iSortIdx values for two WhereLoop are different
      ** then those WhereLoops need to be considered separately.  Neither is
      ** a candidate to replace the other. */
      continue;
    }
    /* In the current implementation, the rSetup value is either zero
    ** or the cost of building an automatic index (NlogN) and the NlogN
    ** is the same for compatible WhereLoops. */
    assert( p->rSetup==0 || pTemplate->rSetup==0 
                 || p->rSetup==pTemplate->rSetup );

    /* whereLoopAddBtree() always generates and inserts the automatic index
    ** case first.  Hence compatible candidate WhereLoops never have a larger
    ** rSetup. Call this SETUP-INVARIANT */
    assert( p->rSetup>=pTemplate->rSetup );

    if( (p->prereq & pTemplate->prereq)==p->prereq
     && p->rSetup<=pTemplate->rSetup
     && p->rRun<=pTemplate->rRun
    ){
      /* This branch taken when p is equal or better than pTemplate in 
      ** all of (1) dependences (2) setup-cost, and (3) run-cost. */
      assert( p->rSetup==pTemplate->rSetup );
      if( p->nLTerm<pTemplate->nLTerm
       && (p->wsFlags & WHERE_INDEXED)!=0
       && (pTemplate->wsFlags & WHERE_INDEXED)!=0
       && p->u.btree.pIndex==pTemplate->u.btree.pIndex
       && p->prereq==pTemplate->prereq
      ){
        /* Overwrite an existing WhereLoop with an similar one that uses
        ** more terms of the index */
        pNext = p->pNextLoop;
        break;








      }else{
        /* pTemplate is not helpful.
        ** Return without changing or adding anything */
        goto whereLoopInsert_noop;
      }
    }



    if( (p->prereq & pTemplate->prereq)==pTemplate->prereq

     && p->rRun>=pTemplate->rRun
     && ALWAYS(p->rSetup>=pTemplate->rSetup) /* See SETUP-INVARIANT above */
    ){
      /* Overwrite an existing WhereLoop with a better one: one that is
      ** better at one of (1) dependences, (2) setup-cost, or (3) run-cost
      ** and is no worse in any of those categories. */


      pNext = p->pNextLoop;
      break;
    }



  }

  /* If we reach this point it means that either p[] should be overwritten
  ** with pTemplate[] if p[] exists, or if p==NULL then allocate a new
  ** WhereLoop and insert it.
  */
#if WHERETRACE_ENABLED