statistics: improve estimation for index equal condition #17366
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eurekaka
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lzmhhh123
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May 22, 2020
| if i >= usedColsLen { | ||
| break | ||
| } | ||
| ndv = mathutil.MaxInt64(ndv, coll.Columns[colID].NDV) |
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Why not use the col1.ndv * col2.ndv * ... instead of max of them?
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If the 2 rows are like (1,1),(2,2), the NDV is 2 not 4. max is lower bound, ndv * ndv is upper bound, using max is consistent with getCardinality().
Codecov Report
@@ Coverage Diff @@
## master #17366 +/- ##
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Coverage 80.0259% 80.0259%
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Files 521 521
Lines 141614 141614
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Hits 113328 113328
Misses 19266 19266
Partials 9020 9020 |
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cherry pick to release-3.0 in PR #17609 |
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cherry pick to release-3.1 in PR #17610 |
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cherry pick to release-4.0 in PR #17611 |
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What problem does this PR solve?
Issue Number: close #17364
Problem Summary:
Wrong plan is chosen when index equal condition contains value which is out of the range of the histogram.
What is changed and how it works?
What's Changed:
Compute the NDV for the prefix columns of the index which are used for equal condition, and use it for row count guess.
How it Works:
It is more reasonable than hard-coded constant
outOfRangeBetweenRate.Related changes
N/A
Check List
Tests
Side effects
N/A
Release note