planner: improve row count estimation for index range containing correlated columns #9738
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/run-all-tests |
Codecov Report
@@ Coverage Diff @@
## master #9738 +/- ##
===============================================
- Coverage 67.2181% 67.2101% -0.008%
===============================================
Files 381 381
Lines 79846 79851 +5
===============================================
- Hits 53671 53668 -3
- Misses 21389 21393 +4
- Partials 4786 4790 +4 |
alivxxx
reviewed
Mar 15, 2019
planner/core/logical_plans.go
Outdated
| hist, ok := ds.statisticTable.Columns[col.ID] | ||
| var ndv float64 | ||
| if ok && hist.Count > 0 { | ||
| factor := float64(ds.statisticTable.Count) / float64(hist.Count) |
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Why ds.statisticTable.Count? This factor does not consider the selectivity of previous index conditions.
zz-jason
reviewed
Mar 18, 2019
zz-jason
reviewed
Mar 19, 2019
| } else { | ||
| profile.Cardinality[i] = profile.RowCount * distinctFactor | ||
| } | ||
| profile.Cardinality[i] = ds.getColumnNDV(col.ID) |
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this seems incorrect, should it be:
hist, ok := ds.statisticTable.Columns[colID]
if ok && hist.Count > 0 {
profile.Cardinality[i] = float64(hist.Count)
} else {
profile.Cardinality[i] = ds.statisticTable.Count
}
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No, cardinality stores NDV not the total row count.
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it's better to s/Cardinality/NDV/ to eliminate ambiguity
alivxxx
added
status/LGT2
kolbe
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to kolbe/tidb
that referenced
this pull request
Mar 20, 2019
eurekaka
added a commit
to eurekaka/tidb
that referenced
this pull request
Mar 28, 2019
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What problem does this PR solve?
Fix #9722
What is changed and how it works?
After appending
col = correlation_colinto access conditions, adjust the estimated row count by multiplying a factor for each condition appended, and the factor is computed as1 / NDV.Check List
Tests
Code changes
N/A
Side effects
N/A
Related changes