数据字典表Truncate掉将导致数据库不可用

     在实际的工作环境下，如果你在操作时将数据库内的几个数据字典表Truncate掉，将会直接导致数据库不能再继续使用，本文将针对一个相关案例进行详细的讲解。

案例如下：

数据库环境：数据库9.2.0.7 RAC。（注：由于数据库的事务量体别大，所以数据库没有进行备份）。

检查后发现的被截断表：

SQL> select object_name,object_type from dba_objects where object_name like 'IDL%';

OBJECT_NAME            OBJECT_TYPE
------------------- ------------------
IDL_CHAR$                 TABLE
IDL_SB4$                  TABLE
IDL_UB1$                  TABLE
IDL_UB2$                  TABLE

IDL_UB1$表是特别重要的字典表，只要出现故障，数据库就会出现大量的ORA-00600错误，所有事务将不能进行。

ORA-00600: internal error code, arguments: [17069],

[0xC0000000DDDFA690], [], [], [], [], [], []

ORA-600 17069错误是一个特别难解决的问题，问题出现后数据库的某个跟踪日志很快就会出现暴涨的情况，因为IDL系列字典表是记录数据库对象编译信息的，丢失了其中的数据，所有过程、Package等都将无法执行。

字典表作用的说明：

IDL_UB1$ is one of four tables that hold compiled PL/SQL code:

IDL_UB1$
IDL_CHAR$
IDL_UB2$
IDL_SB4$

"PL/SQL is based on the programming language Ada. As a result, PL/SQL uses a
variant of Descriptive Intermediate Attributed Notation for Ada (DIANA), which
is a tree-structured intermediate language. It is defined using a meta-notation
called Interface Definition Language (IDL). DIANA provides for communication
internal to compilers and other tools.

"At compile time, PL/SQL source code is translated into machine-readable
m-code.Both the DIANA and m-code for a procedure or package are stored in the
database.At run time, they are loaded into the shared (memory) pool. The DIANA is
used to compile dependent procedures; the m-code is simply executed."

These four tables hold the DIANA and the so-code m-code. I think "m-code" is
short for machine-dependent byte code but there is a sizable machine-indenpendent part

as well. If you have a look at sql.bsq, you can see
that  documents the "type" column of these tables as follows:
part number not null,
/* part: 0 = diana, 1 = portable pcode, 
2 = machine-dependentpcode */

如果出现更为严重的情况，它将导致大量系统DBMS包失效，其重新编译也将更为复杂。

恢复数据库，消除所有ORA-600错误的方法：

恢复的方法是通过运行相关的脚本，重建和重新编译所有Procedure/Trigger/Package等对象，重新生成这些对象的DIANA和so-code m-code，主要包括catlog.sql,catproc.sql等脚本。

注意：即使以花费大量的时间为代价，一些ORA-00600错误也必须解决。

【责编:Ken】

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