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The limit on memory consumption for the range optimizer. A value of 0 means “no limit.”  If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Limiting Memory Use for Range Optimization. 

• rbr_exec_mode 

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For internal use by mysqlbinlog . This variable switches the server between IDEMPOTENT  mode and STRICT  mode. IDEMPOTENT  mode causes suppression of duplicate-key and no-key-found errors in BINLOG  statements generated by mysqlbinlog . This mode is useful when replaying a row-based binary log on a server that causes conflicts with existing data. mysqlbinlog  sets this mode when you specify the --idempotent  option by writing the following to the output: 

As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation. 

• read_buffer_size 

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Each thread that does a sequential scan for a MyISAM  table allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which 

