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MySQL 9.4 Reference Manual

The following system variables affect optimizer tracing:

optimizer_trace: Enables or disables optimizer tracing. SeeSection 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}
```
SeeSection 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. SeeSection 10.15.4, “Tuning Trace Purging”, for more information.
optimizer_trace_offset: Offset of the first trace shown. SeeSection 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. SeeSection 10.15.9, “The end_markers_in_json System Variable”.