englefly opened a new pull request, #55472:
URL: https://github.com/apache/doris/pull/55472
### What problem does this PR solve?
In the current version, we determine whether a value is a hot value based on
its occurrence proportion. However, this method gives rise to two issues:
1. If the number of rows in the table is small, even if a value appears only
once, it will still be identified as a hot value — which increases the overhead
of statistical information derivation.
2. If the number of rows in the table is large (e.g., 10 million) and the
ndv (Number of Distinct Values) is also large (e.g., 10,000), the average
number of occurrences per value is 1000. In this case, if a value accounts for
10% of the total, its actual occurrences will reach 1 million — 1000 times the
average. If such a value is not estimated as a hot value, it will result in a
1000-fold error.
Therefore, we revise the criteria for identifying hot values to:
Actual number of occurrences > Average number of occurrences ×
hot_value_threshold
where hot_value_threshold is a session variable with a default value of 10.
Issue Number: close #xxx
Related PR: #xxx
Problem Summary:
### Release note
None
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [ ] Regression test
- [ ] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason <!-- Add your reason? -->
- Behavior changed:
- [ ] No.
- [ ] Yes. <!-- Explain the behavior change -->
- Does this need documentation?
- [ ] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR should
merge into -->
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