optimizer_trace: Enables or disables optimizer tracing. See Section 8.15.8, “The optimizer_trace System Variable”.

optimizer_trace_features: Enables or disables selected features of the MySQL Optimizer, using the syntax shown here:

SET optimizer_trace_features=option=value[,option=value][,...]

option: 
  {greedy_search | range_optimizer | dynamic_range | repeated_subselect}

value:
  {on | off | default}

See Section 8.15.10, “Selecting Optimizer Features to Trace”, for more information on the effects of these.

optimizer_trace_max_mem_size: Maximum amount of memory that can be used for storing all traces.

optimizer_trace_limit: The maximum number of optimizer traces to be shown. See Section 8.15.4, “Tuning Trace Purging”, for more information.

optimizer_trace_offset: Offset of the first trace shown. See Section 8.15.4, “Tuning Trace Purging”.

end_markers_in_json: If set to 1, causes the trace to repeat the key (if present) near the closing bracket. This also affects the output of EXPLAIN FORMAT=JSON in those versions of MySQL which support this statement. See Section 8.15.9, “The end_markers_in_json System Variable”.