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Overview
| Comment: | Enhance the comment on whereLoopAddBtree(). No changes to code. |
|---|---|
| Downloads: | Tarball | ZIP archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
b22dd165da227a52d88b17a91e80a170 |
| User & Date: | drh 2014-07-22 12:05:32.008 |
Context
|
2014-07-22
| ||
| 14:42 | Expire prepared statements after running ANALYZE. (check-in: b083a961f8 user: drh tags: trunk) | |
| 12:05 | Enhance the comment on whereLoopAddBtree(). No changes to code. (check-in: b22dd165da user: drh tags: trunk) | |
| 00:40 | For the OR-optimization, avoid generating OP_OpenRead opcodes that reopen exactly the same index. (check-in: b67a6e33f2 user: drh tags: trunk) | |
Changes
Changes to src/where.c.
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**
** 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 */
| > > > > > > > > | 4573 4574 4575 4576 4577 4578 4579 4580 4581 4582 4583 4584 4585 4586 4587 4588 4589 4590 4591 4592 4593 4594 |
**
** 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.
**
** The estimated values (nRow, nVisit, nSeek) often contain a large amount
** of uncertainty. For this reason, scoring is designed to pick plans that
** "do the least harm" if the estimates are inaccurate. For example, a
** log(nRow) factor is omitted from a non-covering index scan in order to
** bias the scoring in favor of using an index, since the worst-case
** performance of using an index is far better than the worst-case performance
** of a full table scan.
*/
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 */
|
| ︙ | ︙ |