Function optimizeDupKeyCheckForNormalInsert

pkg/executor/insert.go:330–341

optimizeDupKeyCheckForNormalInsert trys to optimize the DupKeyCheckMode for an insert statement according to the transaction and system variables. If the DupKeyCheckMode of the current statement can be optimized, it will return `DupKeyCheckLazy` to avoid the redundant requests to TiKV, otherwise, `D

(vars *variable.SessionVars, txn kv.Transaction)

// This method only works for "normal" insert statements, that means the options like "IGNORE" and "ON DUPLICATE KEY"
// in a statement are not considerate, and callers should handle the above cases by themselves.
func optimizeDupKeyCheckForNormalInsert(vars *variable.SessionVars, txn kv.Transaction) table.DupKeyCheckMode {
	if !vars.ConstraintCheckInPlace || txn.IsPessimistic() || txn.IsPipelined() {
		// We can just check duplicated key lazily without keys in storage for the below cases:
		// - `txn.Pipelined()` is true.
		//    It means the user is using `@@tidb_dml_type="bulk"` to insert rows in bulk mode.
		//    DupKeyCheckLazy should be used to improve the performance.
		// - The current transaction is pessimistic. The duplicate key check can be postponed to the lock stage.
		// - The current transaction is optimistic but `tidb_constraint_check_in_place` is set to false.
		return table.DupKeyCheckLazy
	}
	return table.DupKeyCheckInPlace
}

// getPessimisticLazyCheckMode returns the lazy check mode for pessimistic txn.
// The returned `PessimisticLazyDupKeyCheckMode` only takes effect for pessimistic txn with `DupKeyCheckLazy`;