ORA-00060的示例与若干场景-mysql教程

对于批量更新，和上面一个事务中多个表操作的原理相同，并发大则也会导致deadlock。要么减少并发，要么不用批量更新。其实出现de

create table eg_60 ( num number, txt varchar2(10) );

insert into eg_60 values ( 1, 'First' );

insert into eg_60 values ( 2, 'Second' );

SQL> select rowid, num, txt from eg_60;

ROWID NUM TXT
------------------ ---------- ----------
AAAQT2AAHAAAEdYAAA 1 First
AAAQT2AAHAAAEdYAAB 2 Second

Session1：

update eg_60 set txt='ses1' where num=1;

Session2：

update eg_60 set txt='ses2' where num=2;

update eg_60 set txt='ses2' where num=1;

Session1：

update eg_60 set txt='ses1' where num=2;

此时Session2报的错：

update eg_60 set txt='ses2' where num=1
*
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource

Session1的update eg_60 set txt='ses1' where num=2;仍处hang状态，此时Session2执行exit正常退出，则

Session1：

update eg_60 set txt='ses1' where num=2;

1 row updated.

原因就是正常退出，Oracle的PMON会自动rollback所做的未Commit操作，释放了num=2的资源，因此Session1可以执行。

出现60错误会产生一个trace文件，查看trace文件位置：

show parameter user_dump
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
user_dump_dest string /opt/app/ora10g/admin/petest/udump

查看trace文件：

Deadlock graph:
---------Blocker(s)-------- ---------Waiter(s)---------
Resource Name process session holds waits process session holds waits
TX-00090004-00019887 25 478 X 24 459 X
TX-000a002d-00032a8d 24 459 X 25 478 X
session 478: DID 0001-0019-00027AEC session 459: DID 0001-0018-000CDDD8
session 459: DID 0001-0018-000CDDD8 session 478: DID 0001-0019-00027AEC
Rows waited on:
Session 459: obj - rowid = 000104F6 - AAAQT2AAHAAAEdYAAB
(dictionary objn - 66806, file - 7, block - 18264, slot - 1)
Session 478: obj - rowid = 000104F6 - AAAQT2AAHAAAEdYAAA
(dictionary objn - 66806, file - 7, block - 18264, slot - 0)
Information on the OTHER waiting sessions:
Session 459:
pid=24 serial=34722 audsid=899246 user: 65/DCSOPEN
O/S info: user: dcsopen, term: pts/0, ospid: 8838, machine: vm-vmw4131-t
program: sqlplus@vm-vmw4131-t (TNS V1-V3)
application name: SQL*Plus, hash value=3669949024
Current SQL Statement:
update eg_60 set txt='ses1' where num=2
End of information on OTHER waiting sessions.
Current SQL statement for this session:
update eg_60 set txt='ses2' where num=1
===================================================

这里66806代表的OBJECT_ID对应object是eg_60。当前执行的SQL是update eg_60 set txt='ses2' where num=1，是这条SQL报的60错误，原因是由于update eg_60 set txt='ses1' where num=2这条SQL。因为这里是在同一台机器开的两个session，如果是不同机器客户端访问数据库做的这个实验，就可以根据machine: vm-vmw4131-t知道是哪个客户端执行的这条SQL。

通过PROCESS STATE节中O/S info: user: dcsopen, term: pts/1, ospid: 13112, machine: vm-vmw4131-t也可以知道是哪个客户端执行SQL报的60错误。

以上是同一张表不同session之间产生的死锁。还有另外一种场景，也是之前这边应用碰到的问题，即不同表之间的死锁，刚刚初步得解的，其实上述两种都属于事务级别的死锁，这里可能说的不准确，，就是因为执行一个SQL后没有commit或rollback，再执行另外一个SQL，这两个SQL形成一个事务，造成可能的死锁。

关于事务，Concept中的解释：

A transaction is a logical unit of work that contains one or more SQL statements. A transaction is an atomic unit. The effects of all the

SQL statements in a transaction can be either all committed (applied to the database) or all rolled back (undone from the database).

A transaction begins with the first executable SQL statement. A transaction ends when it is committed or rolled back, either explicitly

with a COMMIT or ROLLBACK statement or implicitly when a DDL statement is issued.

比如：

Session1：

UPDATE TABLE1，UPDATE TABLE2 ...

Session2：

DELETE TABLE2， DELETE TABLE1 ...

此时碰巧可能出现互相持有对方需要的资源，导致deadlock。

对于这种情况，可能的解决方法就是：将表的顺序改为一致，或者拆分更小的事务，避免较差更新的情况。