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MDEV-20519: Query plan regression with optimizer_use_condition_select…
…ivity > 1 The issue here is the wrong estimate of the cardinality of a partial join, the cardinality is too high because the function table_cond_selectivity() returns an absurd number 100 while selectivity cannot be greater than 1. When accessing table t by outer reference t1.a via index we do not perform any range analysis for t. Yet we see TABLE::quick_key_parts[key] and TABLE->quick_rows[key] contain a non-zero value though these should have been remained untouched and equal to 0. Thus real cause of the problem is that TABLE::init does not clean the arrays TABLE::quick_key_parts[] and TABLE::>quick_rows[]. It should have done it because the TABLE structure created for any instance of a table can be reused for many queries.
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Varun Gupta
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Nov 7, 2019
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