zoukankan html css js c++ java

[bbk3205] 第68集 Chapter 17Monitoring and Detecting Lock Contention(01)

DML Locks

A DML transaction gets at least two blocks:

A shared table lock
An exclusive row lock

A shared table lock主要是阻止DDL语句对当前表进行修改.

An exclusive row lock主要是阻止别的transaction修改同一条记录.

如何查看锁的信息?

有三个重要的动态性能视图:

v$transaction:记录了当前活动的transaction.

desc v$transaction

SQL> desc v$transaction;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ADDR                                               RAW(8)
 XIDUSN                                             NUMBER
 XIDSLOT                                            NUMBER
 XIDSQN                                             NUMBER
 UBAFIL                                             NUMBER
 UBABLK                                             NUMBER
 UBASQN                                             NUMBER
 UBAREC                                             NUMBER
 STATUS                                             VARCHAR2(16)
 START_TIME                                         VARCHAR2(20)
 START_SCNB                                         NUMBER
 START_SCNW                                         NUMBER
 START_UEXT                                         NUMBER
 START_UBAFIL                                       NUMBER
 START_UBABLK                                       NUMBER
 START_UBASQN                                       NUMBER
 START_UBAREC                                       NUMBER
 SES_ADDR                                           RAW(8)
 FLAG                                               NUMBER
 SPACE                                              VARCHAR2(3)
 RECURSIVE                                          VARCHAR2(3)
 NOUNDO                                             VARCHAR2(3)
 PTX                                                VARCHAR2(3)
 NAME                                               VARCHAR2(256)
 PRV_XIDUSN                                         NUMBER
 PRV_XIDSLT                                         NUMBER
 PRV_XIDSQN                                         NUMBER
 PTX_XIDUSN                                         NUMBER
 PTX_XIDSLT                                         NUMBER
 PTX_XIDSQN                                         NUMBER
 DSCN-B                                             NUMBER
 DSCN-W                                             NUMBER
 USED_UBLK                                          NUMBER
 USED_UREC                                          NUMBER
 LOG_IO                                             NUMBER
 PHY_IO                                             NUMBER
 CR_GET                                             NUMBER
 CR_CHANGE                                          NUMBER
 START_DATE                                         DATE
 DSCN_BASE                                          NUMBER
 DSCN_WRAP                                          NUMBER
 START_SCN                                          NUMBER
 DEPENDENT_SCN                                      NUMBER
 XID                                                RAW(8)
 PRV_XID                                            RAW(8)
 PTX_XID                                            RAW(8)

v$lock:

desc v$lock

SQL> desc v$lock;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ADDR                                               RAW(8)
 KADDR                                              RAW(8)
 SID                                                NUMBER
 TYPE                                               VARCHAR2(2)
 ID1                                                NUMBER
 ID2                                                NUMBER
 LMODE                                              NUMBER
 REQUEST                                            NUMBER
 CTIME                                              NUMBER
 BLOCK                                              NUMBER

v$session:

desc v$session

SQL> desc v$session;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 SADDR                                              RAW(8)
 SID                                                NUMBER
 SERIAL#                                            NUMBER
 AUDSID                                             NUMBER
 PADDR                                              RAW(8)
 USER#                                              NUMBER
 USERNAME                                           VARCHAR2(30)
 COMMAND                                            NUMBER
 OWNERID                                            NUMBER
 TADDR                                              VARCHAR2(16)
 LOCKWAIT                                           VARCHAR2(16)
 STATUS                                             VARCHAR2(8)
 SERVER                                             VARCHAR2(9)
 SCHEMA#                                            NUMBER
 SCHEMANAME                                         VARCHAR2(30)
 OSUSER                                             VARCHAR2(30)
 PROCESS                                            VARCHAR2(24)
 MACHINE                                            VARCHAR2(64)
 PORT                                               NUMBER
 TERMINAL                                           VARCHAR2(30)
 PROGRAM                                            VARCHAR2(48)
 TYPE                                               VARCHAR2(10)
 SQL_ADDRESS                                        RAW(8)
 SQL_HASH_VALUE                                     NUMBER
 SQL_ID                                             VARCHAR2(13)
 SQL_CHILD_NUMBER                                   NUMBER
 SQL_EXEC_START                                     DATE
 SQL_EXEC_ID                                        NUMBER
 PREV_SQL_ADDR                                      RAW(8)
 PREV_HASH_VALUE                                    NUMBER
 PREV_SQL_ID                                        VARCHAR2(13)
 PREV_CHILD_NUMBER                                  NUMBER
 PREV_EXEC_START                                    DATE
 PREV_EXEC_ID                                       NUMBER
 PLSQL_ENTRY_OBJECT_ID                              NUMBER
 PLSQL_ENTRY_SUBPROGRAM_ID                          NUMBER
 PLSQL_OBJECT_ID                                    NUMBER
 PLSQL_SUBPROGRAM_ID                                NUMBER
 MODULE                                             VARCHAR2(48)
 MODULE_HASH                                        NUMBER
 ACTION                                             VARCHAR2(32)
 ACTION_HASH                                        NUMBER
 CLIENT_INFO                                        VARCHAR2(64)
 FIXED_TABLE_SEQUENCE                               NUMBER
 ROW_WAIT_OBJ#                                      NUMBER
 ROW_WAIT_FILE#                                     NUMBER
 ROW_WAIT_BLOCK#                                    NUMBER
 ROW_WAIT_ROW#                                      NUMBER
 TOP_LEVEL_CALL#                                    NUMBER
 LOGON_TIME                                         DATE
 LAST_CALL_ET                                       NUMBER
 PDML_ENABLED                                       VARCHAR2(3)
 FAILOVER_TYPE                                      VARCHAR2(13)
 FAILOVER_METHOD                                    VARCHAR2(10)
 FAILED_OVER                                        VARCHAR2(3)
 RESOURCE_CONSUMER_GROUP                            VARCHAR2(32)
 PDML_STATUS                                        VARCHAR2(8)
 PDDL_STATUS                                        VARCHAR2(8)
 PQ_STATUS                                          VARCHAR2(8)
 CURRENT_QUEUE_DURATION                             NUMBER
 CLIENT_IDENTIFIER                                  VARCHAR2(64)
 BLOCKING_SESSION_STATUS                            VARCHAR2(11)
 BLOCKING_INSTANCE                                  NUMBER
 BLOCKING_SESSION                                   NUMBER
 FINAL_BLOCKING_SESSION_STATUS                      VARCHAR2(11)
 FINAL_BLOCKING_INSTANCE                            NUMBER
 FINAL_BLOCKING_SESSION                             NUMBER
 SEQ#                                               NUMBER
 EVENT#                                             NUMBER
 EVENT                                              VARCHAR2(64)
 P1TEXT                                             VARCHAR2(64)
 P1                                                 NUMBER
 P1RAW                                              RAW(8)
 P2TEXT                                             VARCHAR2(64)
 P2                                                 NUMBER
 P2RAW                                              RAW(8)
 P3TEXT                                             VARCHAR2(64)
 P3                                                 NUMBER
 P3RAW                                              RAW(8)
 WAIT_CLASS_ID                                      NUMBER
 WAIT_CLASS#                                        NUMBER
 WAIT_CLASS                                         VARCHAR2(64)
 WAIT_TIME                                          NUMBER
 SECONDS_IN_WAIT                                    NUMBER
 STATE                                              VARCHAR2(19)
 WAIT_TIME_MICRO                                    NUMBER
 TIME_REMAINING_MICRO                               NUMBER
 TIME_SINCE_LAST_WAIT_MICRO                         NUMBER
 SERVICE_NAME                                       VARCHAR2(64)
 SQL_TRACE                                          VARCHAR2(8)
 SQL_TRACE_WAITS                                    VARCHAR2(5)
 SQL_TRACE_BINDS                                    VARCHAR2(5)
 SQL_TRACE_PLAN_STATS                               VARCHAR2(10)
 SESSION_EDITION_ID                                 NUMBER
 CREATOR_ADDR                                       RAW(8)
 CREATOR_SERIAL#                                    NUMBER
 ECID                                               VARCHAR2(64)

查看自己的session id;根据sesion id确定是哪一个session

SQL> select sid from v$mystat where rownum=1;

       SID
----------
        70

Oracle 不会随着锁住的资源越多，占用的资源越多；因为Oracle将锁信息存放在Blokc header里面的.

INITRANS=2,MAXTRANS=255，这两个参数的含义：默认情况下有2个Transaction同时对同一张表进行加锁事务处理，最大255个Transaction对同一张表进行加锁事务处理.自oracle 10g以后，已经废弃MAXTRANS参数，直接默认就是255.

共享锁的目的是阻止别人获得排他性锁，不阻止别人使用共享锁.

图一（连贯看下面图2）

备注:当用户感觉很慢的时候，就可以查看此数据字典中的数据信息，就可以分析出是否是因为锁的原因导致.(REQUEST=6，表示有存在处于等待的事务.)

图二（紧接着看图三）

图三

another demo

首先执行SQL,暂时不要提交.

其次，执行脚本lock_sys.sql

lock_sys.sql

SELECT addr,xidusn FROM V$TRANSACTION;
SELECT sid,type,id1,id2,lmode,request FROM V$LOCK ORDER BY 1,5;

SELECT sid,type,trunc(id1/power(2,16)) rbs,
        bitand(id1,to_number('ffff','xxxx'))+0 slot,id2 req,lmode,request
FROM v$lock
WHERE sid=137;


SELECT xidusn,xidslot,xidsqn FROM V$TRANSACTION;