Lock

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LockMethodLockHash：存储LOCK
LockMethodProcLockHash：存储PROCLOCK
LockMethodLocalHash：存储LOCALLOCK

同一个LOCK资源对象可以被多个不同的 PROCLOCK 持有，而这些 PROCLOCK 又分别属于不同的进程。

LOCKTAG

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typedef struct LOCKTAG
{
	uint32		locktag_field1; /* a 32-bit ID field */
	uint32		locktag_field2; /* a 32-bit ID field */
	uint32		locktag_field3; /* a 32-bit ID field */
	uint16		locktag_field4; /* a 16-bit ID field */
	uint8		locktag_type;	/* see enum LockTagType */
	uint8		locktag_lockmethodid;	/* lockmethod indicator */
} LOCKTAG;
  • locktag_type
    标识这个锁是针对哪类资源的。每种 LockTagType 决定了 LOCKTAG 里后面几个字段（locktag_field1 ~ locktag_field4）是怎么解释的，比如：
    LOCKTAG_TRANSACTION：xid
    LOCKTAG_RELATION：dbOid + relOid
    LOCKTAG_TUPLE：dbOid + relOid + blockNum + offNum
  • locktag_lockmethodid
    • DEFAULT_LOCKMETHOD（id = DEFAULT_LOCKMETHOD)
      绝大多数用户可见的锁（relation, tuple, transactionid 等）都走它。
    • USER_LOCKMETHOD（id = USER_LOCKMETHOD)
      提供给 pg_advisory_lock() 一类的 advisory lock，用于用户自定义锁。

LOCK

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typedef struct LOCK
{
	LOCKTAG		tag;			
	LOCKMASK	grantMask;		
	LOCKMASK	waitMask;		
	dlist_head	procLocks;		
	dclist_head     waitProcs;		
	int		requested[MAX_LOCKMODES];	
	int		nRequested;		
	int		granted[MAX_LOCKMODES]; 
	int		nGranted;		
} LOCK;
  • waitProcs
    等待本LOCK的PGPROC链表
  • procLocks
    等待本LOCK的PROCLOCK链表
  • waitMask
    该资源上等待的锁类型
  • grantMask
    该资源上已经授予的锁类型

LOCKMODE

每种资源支持8种锁

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#define NoLock					0
#define AccessShareLock			1	/* SELECT */
#define RowShareLock			2	/* SELECT FOR UPDATE/FOR SHARE */
#define RowExclusiveLock		3	/* INSERT, UPDATE, DELETE */
#define ShareUpdateExclusiveLock 4	/* VACUUM (non-FULL), ANALYZE, CREATE
									 * INDEX CONCURRENTLY */
#define ShareLock				5	/* CREATE INDEX (WITHOUT CONCURRENTLY) */
#define ShareRowExclusiveLock	6	/* like EXCLUSIVE MODE, but allows ROW
									 * SHARE */
#define ExclusiveLock			7	/* blocks ROW SHARE/SELECT...FOR UPDATE */
#define AccessExclusiveLock		8	/* ALTER TABLE, DROP TABLE, VACUUM FULL,
									 * and unqualified LOCK TABLE */

#define MaxLockMode				8	/* highest standard lock mode */

冲突矩阵

Requested Lock Mode ACCESS SHARE ROW SHARE ROW EXCL. SHARE UPDATE EXCL. SHARE SHARE ROW EXCL. EXCL. ACCESS EXCL.
ACCESS SHARE X
ROW SHARE X X
ROW EXCL. X X X X
SHARE UPDATE EXCL. X X X X X
SHARE X X X X X
SHARE ROW EXCL. X X X X X X
EXCL. X X X X X X X
ACCESS EXCL. X X X X X X X X

参考链接

postgres官方文档