Oracle ORA-01555(快照过旧)
ORA-01555 快照过旧,是数据库中很常见的一个错误,比如当我们的事务需要使用undo来构建CR块的时候,而此时对应的undo已经不存在
一、引言:
[Oracle@]$ oerr ora 01555
01555, 00000, "snapshot too old: rollback segment number %s with name \"%s\" too small"
// *Cause: rollback records needed by a reader for consistent read are
// overwritten by other writers
// *Action: If in Automatic Undo Management mode, increase undo_retention
// setting. Otherwise, use larger rollback segments
ORA-01555 快照过旧,是数据库中很常见的一个错误,比如当我们的事务需要使用undo来构建CR块的时候,而此时对应的undo已经不存在了,这个时候就会报ORA-01555的错误。
ORA-01555错误在Oracle 8i及之前的版本最多。从9i开始的undo自动管理,至现在的10g、11g中的undo auto tuning,使得ORA-01555的错误越来越少。但是这个错误,仍然不可避免。
二、出现ORA-01555错误,通常有2中情况:
(1)、SQL语句执行时间太长,或者undo表空间过小,或者事务量过大,或者过于频繁的提交,,导致执行SQL过程中进行一致性读时,SQL执行后修改的前镜像(既UNDO数据)在UNDO表空间中已经被覆盖,不能构造一致性读块(CR blocks)。这种情况最多。
(2)、SQL语句执行过程中,访问到的块,在进行延迟块清除时,不能确定该块的事务提交时间与SQL执行开始时间的先后次序。这种情况很少。
三、模拟ORA-01555场景:
SQL> create table jack (id int,name varchar2(10));
Table created.
SQL> insert into jack values(1,'a');
1 row created.
SQL> insert into jack values(2,'b');
1 row created.
SQL> commit;
Commit complete.
SQL> show parameter undo
NAME TYPE VALUE
-------------------- ----------- --------------
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDO2
SQL> create undo tablespace undo1 datafile '/u01/app/oracle/oradata/yft/undo01.dbf' size 1m;
Tablespace created.
SQL> alter system set undo_retention=1;
System altered.
SQL> var x refcursor
SQL> begin
2 open :x for select * from jack;
3 end;
4 /
PL/SQL procedure successfully completed.
SQL> begin
2 for i in 1 .. 20000 loop
3 update jack set id=id+1;
4 commit;
5 end loop;
6 end;
7 /
PL/SQL procedure successfully completed.
SQL> print :x
ERROR:
ORA-01555: snapshot too old: rollback segment number 17 with name
"_SYSSMU17_2039231318$" too small
no rows selected
四、第1种情况解决的办法:
(1)、增加UNDO表空间大小;
(2)、增加undo_retention时间,默认只有15分钟;
(3)、优化出错的SQL,减少查询的时间,首选方法;
(4)、避免频繁的提交。
Oracle ORA-01555 快照过旧 说明
ORA-01078 和 LRM-00109 报错解决方法
ORA-01555超长的Query Duration时间
ORA-00471 处理方法笔记
ORA-00314,redolog 损坏,或丢失处理方法
ORA-00257 归档日志过大导致无法存储的解决办法
本文永久更新链接地址:

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