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Overview
Comment:Add text to the header comment of whereLoopAddBtree() describing how the costs of various b-tree loops are estimated.
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SHA1: 05e6e16cb28c9ffb4596bd2ef81f687c5403ecbb
User & Date: dan 2014-04-30 15:00:16
Context
2014-04-30
15:22
Modify the way the costs of various query plans are estimated. If the user supplies a likelihood() value (or equivalent) on an indexed WHERE constraint, use it to estimate the number of index rows visited. check-in: 90e36676 user: dan tags: trunk
15:00
Add text to the header comment of whereLoopAddBtree() describing how the costs of various b-tree loops are estimated. Closed-Leaf check-in: 05e6e16c user: dan tags: experimental-costs
14:53
Update a couple of test cases to account for the fact that this branch prefers an index scan and partial sort over a full-table scan and full external sort. check-in: 9b975bf3 user: dan tags: experimental-costs
Changes
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Changes to src/where.c.

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  return 0;
}

/*
** Add all WhereLoop objects for a single table of the join where the table
** is idenfied by pBuilder->pNew->iTab.  That table is guaranteed to be
** a b-tree table, not a virtual table.























*/
static int whereLoopAddBtree(
  WhereLoopBuilder *pBuilder, /* WHERE clause information */
  Bitmask mExtra              /* Extra prerequesites for using this table */
){
  WhereInfo *pWInfo;          /* WHERE analysis context */
  Index *pProbe;              /* An index we are evaluating */







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  return 0;
}

/*
** Add all WhereLoop objects for a single table of the join where the table
** is idenfied by pBuilder->pNew->iTab.  That table is guaranteed to be
** a b-tree table, not a virtual table.
**
** The costs (WhereLoop.rRun) of the b-tree loops added by this function
** are calculated as follows:
**
** For a full scan, assuming the table (or index) contains nRow rows:
**
**     cost = nRow * 3.0                    // full-table scan
**     cost = nRow * K                      // scan of covering index
**     cost = nRow * (K+3.0)                // scan of non-covering index
**
** where K is a value between 1.1 and 3.0 set based on the relative 
** estimated average size of the index and table records.
**
** For an index scan, where nVisit is the number of index rows visited
** by the scan, and nSeek is the number of seek operations required on 
** the index b-tree:
**
**     cost = nSeek * (log(nRow) + K * nVisit)          // covering index
**     cost = nSeek * (log(nRow) + (K+3.0) * nVisit)    // non-covering index
**
** Normally, nSeek is 1. nSeek values greater than 1 come about if the 
** WHERE clause includes "x IN (....)" terms used in place of "x=?". Or when 
** implicit "x IN (SELECT x FROM tbl)" terms are added for skip-scans.
*/
static int whereLoopAddBtree(
  WhereLoopBuilder *pBuilder, /* WHERE clause information */
  Bitmask mExtra              /* Extra prerequesites for using this table */
){
  WhereInfo *pWInfo;          /* WHERE analysis context */
  Index *pProbe;              /* An index we are evaluating */