Prepare range instructions and do init work for each operator's argument by calling its prepare function.

String range instructions and call each operator's string function to show a query plan.

LastInstructionOp is not a true operator and must set at last.

LockOp is used to add locks to lockservice for pessimistic transactions.

MergeBlock is used to recieve S3 block metLoc Info, and write them to S3.

MergeDelete is used to recieve S3 Blcok Delete Info from remote Cn.

Instruction contains relational algebra.