#explain
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Digging into MariaDB's Source 8: The Optimizer — JOIN::optimize and Choosing a Plan
We follow, in the source, what the MariaDB optimizer does before a single line of EXPLAIN appears — the stages of JOIN::optimize() (tidying the conditions, estimating row counts, range analysis, searching join orders), the new cost model where 1 means one millisecond, how a histogram flips a plan, and where EXPLAIN and optimizer_trace come from — checking each with examples and gdb.