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Overview
Comment:Fix an error in the comments from the previous check-in.
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SHA1: 9660ce541837ccd8df415641a922274e093056aa
User & Date: drh 2014-11-22 19:52:10.008
Context
2014-11-22
21:37
Always reinitialized the Index.bUnordered and Index.noSkipscan flags before rereading the sqlite_stat1 table, even if SQLITE_ENABLE_STAT4 is defined. (check-in: 1e1221fc48 user: drh tags: trunk)
19:52
Fix an error in the comments from the previous check-in. (check-in: 9660ce5418 user: drh tags: trunk)
18:50
Deploy heuristics (well-commented) to better estimate how much unindexed terms in the WHERE clause filter the number of output rows from a single table. (check-in: 221659945c user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/where.c.
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**
** TUNING:  For every WHERE clause term that is not used by the index
** and which does not have an assigned truth probability, heuristics
** described below are used to try to estimate the truth probability.
** TODO --> Perhaps this is something that could be improved by better
** table statistics.
**
** Heuristic 1:  Estimate the truth probability as 6.25%.  The 6.25%
** value corresponds to 1 in LogEst notation, so this means decrement
** the WhereLoop.nOut field for every such WHERE clause term.
**
** Heuristic 2:  If there exists one or more WHERE clause terms of the
** form "x==EXPR" and EXPR is not a constant 0 or 1, then make sure the
** final output row estimate is no greater than 1/4 of the total number
** of rows in the table.  In other words, assume that x==EXPR will filter
** out at least 3 out of 4 rows.  If EXPR is -1 or 0 or 1, then maybe the








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4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314

**
** TUNING:  For every WHERE clause term that is not used by the index
** and which does not have an assigned truth probability, heuristics
** described below are used to try to estimate the truth probability.
** TODO --> Perhaps this is something that could be improved by better
** table statistics.
**
** Heuristic 1:  Estimate the truth probability as 93.75%.  The 93.75%
** value corresponds to -1 in LogEst notation, so this means decrement
** the WhereLoop.nOut field for every such WHERE clause term.
**
** Heuristic 2:  If there exists one or more WHERE clause terms of the
** form "x==EXPR" and EXPR is not a constant 0 or 1, then make sure the
** final output row estimate is no greater than 1/4 of the total number
** of rows in the table.  In other words, assume that x==EXPR will filter
** out at least 3 out of 4 rows.  If EXPR is -1 or 0 or 1, then maybe the
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