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The function test_quick_select by mistake did not update the value of table->quick_condition_rows for index intersection scans though the specification explicitly required to do so from any table access plan once the plan provided a better upper bound for the number of rows selected from the table. It resulted in a bogus, usually very big number saved as the cost of the table access. This, in its turn, in many cases forced the optimizer to make a bad choice of the execution plan for join queries.
12 KiB
12 KiB