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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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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | experimental-costs |
| Files: | files | file ages | folders |
| SHA1: |
05e6e16cb28c9ffb4596bd2ef81f687c |
| User & Date: | dan 2014-04-30 15:00:16 |
Context
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2014-04-30
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| 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
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 */ |