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long长事务回滚的模拟与定位

发表于：2024-12-03 作者：千家信息网编辑

千家信息网最后更新 2024年12月03日，大型事务的回滚大型事务的回滚产生非常大的代价，不仅锁定需要的资源，并且消耗的CPU和IO，尤其是IO将极为密集。尤其在KILL大型事务之前检查事务究竟有多大可能是必要的，同时我们也需要知道回滚已经进

千家信息网最后更新 2024年12月03日long长事务回滚的模拟与定位大型事务的回滚大型事务的回滚产生非常大的代价，不仅锁定需要的资源，并且消耗的CPU和IO，尤其是IO将极为密集。尤其在KILL大型事务之前检查事务究竟有多大可能是必要的，同时我们也需要知道回滚已经进行了多少程度。
一、模拟：

1.删除500多万的数据。

SQL> conn hr/hr;
Connected.
SQL> create table test as select * from dba_objects;

Table created.

SQL> insert into test select * from test;

87055 rows created.

SQL> insert into test select * from test;

174110 rows created.

SQL> insert into test select * from test;

348220 rows created.

SQL> insert into test select * from test;

696440 rows created.

SQL> insert into test select * from test;

1392880 rows created.

SQL> select count(*) from test;

COUNT(*)
----------
2785760

SQL> insert into test select * from test;

2785760 rows created.

SQL> commit;

Commit complete.

SQL> select count(*) from test;

COUNT(*)
----------
5571520

SQL> analyze table test compute statistics;

Table analyzed.

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

SID
----------
30

SQL>

--模拟删除，不commit
SQL> delete test;

5571520 rows deleted.

--另开窗口，查询kill掉会话

SQL> select sid,serial#,sql_id,event,blocking_session from v$session where sid=30;

SID SERIAL# SQL_ID EVENT BLOCKING_SESSION
---------- ---------- ------------- ---------------------------------------------------------------- ----------------
30 165 7qqwcq9td6akt log buffer space 11

SQL> select sql_text from v$sql where sql_id='7qqwcq9td6akt';

SQL_TEXT
----------------------------------------------------------------------
delete test

SQL> alter system kill session '30,165' immediate;

System altered.

--回到原来窗口验证：
SQL> select count(*) from test;
select count(*) from test
*
ERROR at line 1:
ORA-03135: connection lost contact
Process ID: 28346
Session ID: 30 Serial number: 165

二、定位：
查看回滚进度：
可以通过以下两个视图查看回滚的进度，通过单位时间内恢复的undo block来估算恢复时间：
1. 通过x$ktuxe
alter session set nls_date_format='yyyy-mm-dd hh34:mi:ss';
select ADDR,KTUXEUSN,KTUXESLT,KTUXESQN,KTUXESIZ,sysdate from x$ktuxe where KTUXECFL='DEAD' and KTUXESIZ >0;

SQL> alter session set nls_date_format='yyyy-mm-dd hh34:mi:ss';

Session altered.

SQL> select ADDR,KTUXEUSN,KTUXESLT,KTUXESQN,KTUXESIZ,sysdate from x$ktuxe where KTUXECFL='DEAD' and KTUXESIZ >0;

ADDR KTUXEUSN KTUXESLT KTUXESQN KTUXESIZ SYSDATE
---------------- ---------- ---------- ---------- ---------- -------------------
00007F170E8AAC20 5 11 7784 84438 2017-12-09 14:19:22

SQL>

可以通过KTUXESLT ,KTUXESQN这两个字段，然后用以下脚本回滚得出大概需要的时间：
set serveroutput on
declare
l_start number;
l_end number;
begin
select ktuxesiz
into l_start
from x$ktuxe
where KTUXEUSN = 5
and KTUXESLT = 11;
dbms_lock.sleep(60);
select ktuxesiz
into l_end
from x$ktuxe
where KTUXEUSN = 5
and KTUXESLT = 11;
dbms_output.put_line('time est Day:' ||
round(l_end / (l_start - l_end) / 60 / 24, 2));
end;
/

time est Day:.01

PL/SQL procedure successfully completed.

SQL> SQL>

2. 通过v$fast_start_trancsations 状态为recovering表示恢复中;
select USN,SLT,SEQ,STATE,UNDOBLOCKSDONE,UNDOBLOCKSTOTAL,CPUTIME,XID,sysdate from V$FAST_START_TRANSACTIONS;

SQL> select USN,SLT,SEQ,STATE,UNDOBLOCKSDONE,UNDOBLOCKSTOTAL,CPUTIME,XID,sysdate from V$FAST_START_TRANSACTIONS;

USN SLT SEQ STATE UNDOBLOCKSDONE UNDOBLOCKSTOTAL CPUTIME XID SYSDATE
---------- ---------- ---------- ---------------- -------------- --------------- ---------- ---------------- -------------------
5 11 7784 RECOVERING 123491 179829 120 05000B00681E0000 2017-12-09 14:20:25

通过如下视图观察回滚是串行还是并行回滚的，如下图应是并行恢复的，
V$FAST_START_SERVERS provides information about all the recovery slaves performing parallel transaction recovery.

通过xid字段与v$fast_start_trancsations关联。
select * from v$fast_start_servers where xid in (select XID from V$FAST_START_TRANSACTIONS);

SQL> select * from v$fast_start_servers where xid in (select XID from V$FAST_START_TRANSACTIONS);

STATE UNDOBLOCKSDONE PID XID
----------- -------------- ---------- ----------------
RECOVERING 133950 20 05000B00681E0000

3.查看回滚对象
通过dump undo block方式查看回滚的对象：

首先通过v$fast_start_trancsations的usn字段查询到使用的回滚段。

SQL> select * from v$rollname where usn=5;

USN NAME
---------- ------------------------------
5 _SYSSMU5_898567397$

dump这个undo block，因为dump的文件很大，在查询出对象的object_id后，kill掉这个dump会话。
alter system dump undo block "" XID ;

SQL> alter system dump undo block "_SYSSMU5_898567397$" xid 5 11 7784;

。。。。。。。。。

[oracle@wang trace]$ ls -lrt
total 635992
-rw-r----- 1 oracle oinstall 81 Apr 27 2017 DBdb_ora_9045.trm
-rw-r----- 1 oracle oinstall 59 Apr 27 2017 DBdb_mman_9065.trm
-rw-r----- 1 oracle oinstall 60 Apr 27 2017 DBdb_ora_9084.trm
-rw-r----- 1 oracle oinstall 111 Apr 27 2017 DBdb_ora_9099.trm
.......................................
-rw-r----- 1 oracle oinstall 12306 Dec 9 14:23 DBdb_ora_28113.trm
-rw-r----- 1 oracle oinstall 536798705 Dec 9 14:23 DBdb_ora_28113.trc
[oracle@wang trace]$
[oracle@wang trace]$
[oracle@wang trace]$
[oracle@wang trace]$ grep objn DBdb_ora_28113.trc | head -5
* Rec #0x11 slt: 0x0b objn: 90373(0x00016105) objd: 90373 tblspc: 4(0x00000004)
* Rec #0x10 slt: 0x0b objn: 90373(0x00016105) objd: 90373 tblspc: 4(0x00000004)
* Rec #0xf slt: 0x0b objn: 90373(0x00016105) objd: 90373 tblspc: 4(0x00000004)
* Rec #0xe slt: 0x0b objn: 90373(0x00016105) objd: 90373 tblspc: 4(0x00000004)
* Rec #0xd slt: 0x0b objn: 90373(0x00016105) objd: 90373 tblspc: 4(0x00000004)
[oracle@wang trace]$
[oracle@wang trace]$

可以查询到objn为121192,对应的就是dba_objects的object_id，即mosongtao.rollback_test，正是前边测试的对象。再查询v$session_longops配合username,last_update_time,target，可以大概定位到执行sql_id。

注意：在查询到object_id后手工停掉dump undo block 动作

SQL> alter system dump undo block "_SYSSMU5_898567397$" xid 5 11 7784;

^C^C^C^C^C^C
alter system dump undo block "_SYSSMU5_898567397$" xid 5 11 7784
*
ERROR at line 1:
ORA-01013: user requested cancel of current operation

SQL> SQL> SQL> SQL>

4.查询sql
SQL> select SID,TARGET,SQL_ID,START_TIME,LAST_UPDATE_TIME from v$session_longops where target like '%TEST%' order by LAST_UPDATE_TIME desc;

SID TARGET SQL_ID START_TIME LAST_UPDATE_
---------- ---------------------------------------------------------------- ------------- ------------ ------------
30 HR.TEST 7qqwcq9td6akt 09-DEC-17 09-DEC-17

SQL> select sql_text from v$sql where sql_id='7qqwcq9td6akt';

SQL_TEXT
-------------------------------------------------------------------------
delete test

SQL>

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