Lock Modes
Lock	Row/Table	Prevent	Allows	Acquiring Statements
RS (Row Share)	Row or Table	X, RX on the locked rows	RS, S, SRX, RX on the rows not locked	SELECT … FOR UPDATE LOCK TABLE
RX (Row Exclusive)	Row or Table	X, SRX, S, RX on the locked rows	RS, RX on the rows not locked	INSERT
				UPDATE
				DELETE
				LOCK TABLE
S (Share)	Table	X, SRX, RX	RS, S	LOCK TABLE
SRX (Share Row Exclusive)	Table	X, SRX, S, RX	RS	LOCK TABLE
X (Exclusive)	Table	X, SRX, S, RX, RS		LOCK TABLE

DML Statement	Row Locks?	Mode of Table Lock
SELECT ... FROM table
INSERT INTO table ...	X	RX
UPDATE table ...	X	RX
DELETE FROM table ...	X	RX
SELECT ... FROM table ... FOR UPDATE OF ...	X	RS
LOCK TABLE table IN ...
ROW SHARE MODE		RS
ROW EXCLUSIVE MODE		RX
SHARE MODE		S
SHARE EXCLUSIVE MODE		SRX
EXCLUSIVE MODE		X

TX锁时V$LOCK视图中ID1列和V$TRANSACTION的关系：
XIDUSN = TRUNC(ID1/POWER(2,16))
XIDSLOT = MOD(ID1,POWER(2,16))

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LOCK