概述
假如，2个会话，并发写入数据：
BEGIN;
INSERT INTO t1 VALUES(1, 'data1');
COMMIT;
BEGIN;
INSERT INTO t1 VALUES(1, 'data2');
COMMIT;
加锁逻辑：
exec_simple_query
pg_parse_query
pg_analyze_and_rewrite
pg_plan_queries
PortalStart
PortalRun
PortalRunMulti
ProcessQuery
ExecutorStart
standard_ExecutorStart
InitPlan
ExecInitNode
ExecInitModifyTable
ExecInitResultRelation
ExecGetRangeTableRelation
table_open(relation, 'RowExclusiveLock') # 8级锁，行级排他锁
relation_open
LockRelationOid
LockAcquire
ExecutorRun
standard_ExecutorRun
ExecutePlan
...
ExecInsert
table_tuple_insert
heapam_tuple_insert
heap_insert
RelationGetBufferForTuple
LockBuffer
LWLockAcquire(buffer, 'LW_EXCLUSIVE') # 读写锁
RelationPutHeapTuple
log_heap_insert
锁
HWLock
- 8级
- relation, index, buffer
- 死锁检测
LWLocks
- buffer
SpinLock
PresicateLock
HWLock
| 锁 | 取值 | 操作 |
|---|---|---|
| AccessShareLock | 1 | SELECT |
| RowShareLock | 2 | SELECT FOR UPDATE/SHARE |
| RowExclusiveLock | 3 | INSERT/UPDATE/DELETE |
| ShareUpdateExclusiveLock | 4 | VACUUM/ANALYZE/CRATE INDEX CONCURRENTLY |
| ShareLock | 5 | CREATE INDEX |
| ShareRowExclusiveLock | 6 | row share |
| ExclusiveLock | 7 | block ROW SHARE/SELECT FOR UPDATE |
| AccessExclusiveLock | 8 | ALTER TABLE/DROP TABLE/VACUUM FULL |
LockRelationOid
LockAcquireExtended
hash_search
所有进程共享
LWLocks
类似信号量
- LW_SHARED
- LW_EXCLUSIVE
LWLockAcquire
| 目标 | 工具/方法 |
|---|---|
| 查看当前所有 heavyweight locks | SELECT * FROM pg_locks; |
| 查看 LWLock 等待统计 | SELECT * FROM pg_stat_activity WHERE wait_event_type = 'LWLock'; |
| 查看 LWLock 累计统计 | SELECT * FROM pg_stat_lwlocks; (PG16 新增) |
| 跟踪锁获取/释放 | GDB 断点 LockAcquireExtended, LWLockAcquire |
| 分析死锁 | 日志 deadlock detected + pg_locks 快照 |
| 观察 SSI 谓词锁 | debug_parallel_query = off + GDB PredicateLockTuple |