The following system variables affect optimizer tracing:
optimizer_trace
: Enables or disables optimizer tracing. See Section 10.15.8, “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 10.15.10, “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 10.15.4, “Tuning Trace Purging”, for more information.optimizer_trace_offset
: Offset of the first trace shown. See Section 10.15.4, “Tuning Trace Purging”.end_markers_in_json
: If set to1
, causes the trace to repeat the key (if present) near the closing bracket. This also affects the output ofEXPLAIN FORMAT=JSON
in those versions of MySQL which support this statement. See Section 10.15.9, “The end_markers_in_json System Variable”.