PG 锁类型、级别、死锁解决

文章目录

锁类型
- ACCESS SHARE
- ROW SHARE
- ROW EXCLUSIVE
- SHARE UPDATE EXCLUSIVE
- SHARE
- SHARE ROW EXCLUSIVE
- EXCLUSIVE
- ACCESS EXCLUSIVE
死锁查询
死锁处理
- 死锁测试
- - Session A
  - Session B
  - Session C
  - Session D
  - Session E
  - 原因
结论

锁类型

ACCESS SHARE

1、SELECT产生的锁
2、与ACCESS EXCLUSIVE冲突

ROW SHARE

1、SELECT FOR UPDATE 、SELECT FOR SHARE 产生的锁
2、与EXCLUSIVE 、ACCESS EXCLUSIVE冲突

ROW EXCLUSIVE

1、UPDATE, DELETE、与INSERT产生的锁
2、与SHARE、SHARE ROW EXCLUSIVE,、EXCLUSIVE、ACCESS EXCLUSIVE冲突

SHARE UPDATE EXCLUSIVE

1、VACUUM (without FULL)、ANALYZE、CREATE INDEX CONCURRENTLY、CREATE STATISTICS、COMMENT ON、 ALTER TABLE VALIDATE 、 other ALTER TABLE variants 产生的锁
2、与SHARE UPDATE EXCLUSIVE、SHARE、SHARE ROW EXCLUSIVE、EXCLUSIVE、ACCESS EXCLUSIVE冲突

1、CREATE INDEX产生的锁
2、与ROW EXCLUSIVE、SHARE UPDATE EXCLUSIVE、SHARE ROW EXCLUSIVE、EXCLUSIVE、ACCESS EXCLUSIVE冲突

SHARE ROW EXCLUSIVE

1、CREATE COLLATION、CREATE TRIGGER、and many forms of ALTER TABLE产生的锁
2、与ROW EXCLUSIVE、SHARE UPDATE EXCLUSIVE、SHARE、SHARE ROW EXCLUSIVE、EXCLUSIVE、and ACCESS EXCLUSIVE 冲突

EXCLUSIVE

1、刷新物化视图REFRESH MATERIALIZED VIEW CONCURRENTLY产生的锁
2、与ROW SHARE、ROW EXCLUSIVE、SHARE UPDATE EXCLUSIVE、SHARE、SHARE ROW EXCLUSIVE、EXCLUSIVE、ACCESS EXCLUSIVE冲突

ACCESS EXCLUSIVE

1、DROP TABLE、TRUNCATE、REINDEX、CLUSTER、VACUUM FULL、REFRESH MATERIALIZED VIEW (without CONCURRENTLY)产生的锁
2、与ACCESS SHARE、ROW SHARE、ROW EXCLUSIVE、SHARE UPDATE EXCLUSIVE、SHARE、SHARE ROW EXCLUSIVE、EXCLUSIVE、ACCESS EXCLUSIVE冲突

死锁查询

with
t_wait as
(    select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.granted,   a.objid,a.objsubid,a.pid,a.virtualtransaction,a.virtualxid,a.transactionid,a.fastpath,    b.state,b.query,b.xact_start,b.query_start,b.usename,b.datname,b.client_addr,b.client_port,b.application_name   from pg_locks a,pg_stat_activity b where a.pid=b.pid and not a.granted
),
t_run as
(   select a.mode,a.locktype,a.database,a.relation,a.page,a.tuple,a.classid,a.granted,   a.objid,a.objsubid,a.pid,a.virtualtransaction,a.virtualxid,a.transactionid,a.fastpath,   b.state,b.query,b.xact_start,b.query_start,b.usename,b.datname,b.client_addr,b.client_port,b.application_name   from pg_locks a,pg_stat_activity b where a.pid=b.pid and a.granted
),
t_overlap as
(   select r.* from t_wait w join t_run r on   (   r.locktype is not distinct from w.locktype and   r.database is not distinct from w.database and   r.relation is not distinct from w.relation and   r.page is not distinct from w.page and   r.tuple is not distinct from w.tuple and   r.virtualxid is not distinct from w.virtualxid and   r.transactionid is not distinct from w.transactionid and   r.classid is not distinct from w.classid and   r.objid is not distinct from w.objid and   r.objsubid is not distinct from w.objsubid and   r.pid <> w.pid   )
),
t_unionall as
(    select r.* from t_overlap r    union all    select w.* from t_wait w
)
select locktype,datname,relation::regclass,page,tuple,virtualxid,transactionid::text,classid::regclass,objid,objsubid,
string_agg(
'Pid: '||case when pid is null then 'NULL' else pid::text end||chr(10)||
'Lock_Granted: '||case when granted is null then 'NULL' else granted::text end||' , Mode: '||case when mode is null then 'NULL' else mode::text end||' , FastPath: '||case when fastpath is null then 'NULL' else fastpath::text end||' , VirtualTransaction: '||case when virtualtransaction is null then 'NULL' else virtualtransaction::text end||' , Session_State: '||case when state is null then 'NULL' else state::text end||chr(10)||
'Username: '||case when usename is null then 'NULL' else usename::text end||' , Database: '||case when datname is null then 'NULL' else datname::text end||' , Client_Addr: '||case when client_addr is null then 'NULL' else client_addr::text end||' , Client_Port: '||case when client_port is null then 'NULL' else client_port::text end||' , Application_Name: '||case when application_name is null then 'NULL' else application_name::text end||chr(10)||
'Xact_Start: '||case when xact_start is null then 'NULL' else xact_start::text end||' , Query_Start: '||case when query_start is null then 'NULL' else query_start::text end||' , Xact_Elapse: '||case when (now()-xact_start) is null then 'NULL' else (now()-xact_start)::text end||' , Query_Elapse: '||case when (now()-query_start) is null then 'NULL' else (now()-query_start)::text end||chr(10)||
'SQL (Current SQL in Transaction): '||chr(10)||
case when query is null then 'NULL' else query::text end,
chr(10)||'--------'||chr(10)
order by    (  case mode    when 'INVALID' then 0   when 'AccessShareLock' then 1   when 'RowShareLock' then 2   when 'RowExclusiveLock' then 3   when 'ShareUpdateExclusiveLock' then 4   when 'ShareLock' then 5   when 'ShareRowExclusiveLock' then 6   when 'ExclusiveLock' then 7   when 'AccessExclusiveLock' then 8   else 0   end  ) desc,   (case when granted then 0 else 1 end)
) as lock_conflict
from t_unionall
group by
locktype,datname,relation,page,tuple,virtualxid,transactionid::text,classid,objid,objsubid ;

死锁处理

死锁测试

Session A

Session B

Session C

Session D

Session E

查询死锁情况

原因

truncate操作触发ACCESS EXCLUSIVE，导致不能查询，所以遇到死锁，可以按锁的级别从高往低释放

查询正常

结论

发生死锁，可以按锁的级别从高往低释放