metrics,planner: add 'pseudo estimation' reason in the metrics #21911
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The reason could be 'outdate' or 'nodata'
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The reason could be 'outdate' or 'nodata'
What problem does this PR solve?
As the title says: add 'pseudo estimation' reason in the metrics.
Problem Summary:
From an ONCALL issue, I find the query plan changes periodically and sometimes uses pseudo statistics and the bad plan makes the whole cluster overload.
The statistics data is healthy and not seems to be outdated. So why TiDB use pseudo estimation?
What is changed and how it works?
What's Changed:
Add a 'type' field to the metrics, the value can be 'outdate' or 'nodata'
How it Works:
Modify metrics
Related changes
Check List
Tests
Release note