8.2 System Variables Controlling the Trace

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

--optimizer-trace=name 
                     Controls tracing of the Optimizer:
 --optimizer-trace-features=name 
                     Enables/disables tracing of selected features of the
                     Optimizer:
                     optimizer_trace_features=option=val[,option=val...],
                     where option is one of {greedy_search, range_optimizer,
                     dynamic_range, repeated_subselect} and val is one of {on,
                     off, default}
 --optimizer-trace-limit=# 
                     Maximum number of shown optimizer traces
 --optimizer-trace-max-mem-size=# 
                     Maximum allowed cumulated size of stored optimizer traces
 --optimizer-trace-offset=# 
                     Offset of first optimizer trace to show; see manual
 --end-markers-in-json=#
                     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.