Server System Variables 864 might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations. The  rand_seed1  and  rand_seed2  variables exist as session variables only, and can be set but not read. The variables—but not their values—are shown in the output of  SHOW VARIABLES . The purpose of these variables is to support replication of the  RAND()  function. For statements that invoke  RAND() , the source passes two values to the replica, where they are used to seed the random number generator. The replica uses these values to set the session variables  rand_seed1  and rand_seed2  so that  RAND()  on the replica generates the same value as on the source. See the description for  rand_seed1 . The size in bytes of blocks that are allocated when doing range optimization. • rand_seed1 • rand_seed2 • range_alloc_block_size • range_optimizer_max_mem_size Command-Line Format --range-optimizer-max-mem-size=# System Variable range_optimizer_max_mem_size Scope Global, Session Dynamic Yes SET_VAR  Hint Applies No Type Integer Command-Line Format --range-alloc-block-size=# System Variable range_alloc_block_size Scope Global, Session Dynamic Yes SET_VAR  Hint Applies Yes Type Integer Default Value 4096 Minimum Value 4096 Maximum Value (64-bit platforms) 18446744073709547520 Maximum Value 4294967295 Block Size 1024 System Variable rand_seed1 Scope Session Dynamic Yes SET_VAR  Hint Applies No Type Integer