plan, stats: fix inconsistent row count estimation #7233
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alivxxx
changed the title
alivxxx
commented
Aug 1, 2018
statistics/selectivity.go
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| // (1): The stats type, always prefer the primary key or index. | ||
| // (2): The number of expression that it covers, the more the better. | ||
| // (3): The number of columns that it contains, the less the better. | ||
| if (bestTp == colType && set.tp < colType) || bestCount < bits || (bestCount == bits && bestNumCols > set.numCols) { |
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It is required by this PR, because after the change in logical_plans.go, it would cause failure in TestIndexRead, it would sometimes choose index (b,c).
ngaut
reviewed
Aug 1, 2018
executor/analyze.go
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| @@ -41,11 +41,13 @@ type AnalyzeExec struct { | |||
| tasks []*analyzeTask | |||
| } | |||
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| // MaxBucketSize is the maximum number of bucket that a histogram could contain. | |||
| var MaxBucketSize = int64(256) | |||
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This is not a good design. Do not export a variable.
winoros
reviewed
Aug 2, 2018
executor/analyze.go
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| @@ -357,3 +358,13 @@ func (e *AnalyzeColumnsExec) buildStats() (hists []*statistics.Histogram, cms [] | |||
| } | |||
| return hists, cms, nil | |||
| } | |||
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| // SetMaxBucketSize sets the `maxBucketSize`. | |||
| func SetMaxBucketSize(size int64) { | |||
coocood
reviewed
Aug 6, 2018
statistics/selectivity.go
Outdated
| // (1): The stats type, always prefer the primary key or index. | ||
| // (2): The number of expression that it covers, the more the better. | ||
| // (3): The number of columns that it contains, the less the better. | ||
| if (bestTp == colType && set.tp < colType) || bestCount < bits || (bestCount == bits && bestNumCols > set.numCols) { |
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I think set.tp != colType is better, because the type is not a scalar.
winoros
approved these changes
Aug 6, 2018
zhexuany
reviewed
Aug 6, 2018
| @@ -35,6 +35,8 @@ type exprSet struct { | |||
| mask int64 | |||
| // ranges contains all the ranges we got. | |||
| ranges []*ranger.Range | |||
| // numCols is the number of columns contained in the index or column(which is always 1). | |||
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If it is always 1, why don't use a const?
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It is always 1 for the column, while it could also greater than 1 for the index.
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/run-all-tests |
alivxxx
added
status/LGT2
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What have you changed? (mandatory)
Sometimes, the estimated count of a smaller set of expression could be smaller than that of a superset, and it is not consistent. This PR fixes it by preferring the estimation of the superset because it could use more stats info.
What is the type of the changes? (mandatory)
How has this PR been tested? (mandatory)
Unit test.
Does this PR affect documentation (docs/docs-cn) update? (mandatory)
No.
Does this PR affect tidb-ansible update? (mandatory)
No.
Does this PR need to be added to the release notes? (mandatory)
No.
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Add a few positive/negative examples (optional)
PTAL @coocood @zz-jason @winoros