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Overview
Comment:Remove the unexplained extra 3.0 cost factor for the B-tree sorting that is done to implement DISTINCT in the absence of an index to help.
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SHA1: 52571991fcfa2629e8a8354e0c9a62e749a092bf
User & Date: drh 2016-02-11 21:55:23.162
Context
2016-02-11
21:59
Enhance the MSVC makefile to enable building 'testfixture' fully from source code. (check-in: f183e05990 user: mistachkin tags: trunk)
21:55
Remove the unexplained extra 3.0 cost factor for the B-tree sorting that is done to implement DISTINCT in the absence of an index to help. (check-in: 52571991fc user: drh tags: trunk)
21:53
Remove the unused fts5BlobCompare() routine. (check-in: defc762dd1 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/where.c.
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  **
  ** The (Y/X) term is implemented using stack variable rScale
  ** below.  */
  LogEst rScale, rSortCost;
  assert( nOrderBy>0 && 66==sqlite3LogEst(100) );
  rScale = sqlite3LogEst((nOrderBy-nSorted)*100/nOrderBy) - 66;
  rSortCost = nRow + estLog(nRow) + rScale + 16;

  /* TUNING: The cost of implementing DISTINCT using a B-TREE is
  ** similar but with a larger constant of proportionality. 
  ** Multiply by an additional factor of 3.0.  */
  if( pWInfo->wctrlFlags & WHERE_WANT_DISTINCT ){
    rSortCost += 16;
  }

  return rSortCost;
}

/*
** Given the list of WhereLoop objects at pWInfo->pLoops, this routine
** attempts to find the lowest cost path that visits each WhereLoop
** once.  This path is then loaded into the pWInfo->a[].pWLoop fields.








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  **
  ** The (Y/X) term is implemented using stack variable rScale
  ** below.  */
  LogEst rScale, rSortCost;
  assert( nOrderBy>0 && 66==sqlite3LogEst(100) );
  rScale = sqlite3LogEst((nOrderBy-nSorted)*100/nOrderBy) - 66;
  rSortCost = nRow + estLog(nRow) + rScale + 16;








  return rSortCost;
}

/*
** Given the list of WhereLoop objects at pWInfo->pLoops, this routine
** attempts to find the lowest cost path that visits each WhereLoop
** once.  This path is then loaded into the pWInfo->a[].pWLoop fields.
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