MySQL Internals Manual  /  Tracing the Optimizer  /  System Variables Controlling the Trace

8.2 System Variables Controlling the Trace

A brief overview from "mysqld --verbose --help":

                     Controls tracing of the Optimizer:
                     Enables/disables tracing of selected features of the
                     where option is one of {greedy_search, range_optimizer,
                     dynamic_range, repeated_subselect} and val is one of {on,
                     off, default}
                     Maximum number of shown optimizer traces
                     Maximum allowed cumulated size of stored optimizer traces
                     Offset of first optimizer trace to show; see manual
                     In JSON output ("EXPLAIN FORMAT=JSON" and optimizer
                     trace), if set to 1, repeats the structure's key (if it
                     has one) near the closing bracket

Those options are described in more detail later in this section.