最近一段时间，发现不少pub上不少新手都因为一时大意，添加数据文件名称不规范，然后想重命名该数据文件（或者想删除该数据文件然后重建），处理思路有些不妥，导致一些悲剧的发现，我这里通过实验提供一个自认为比较合理的处理思路：处理思路是数据文件离线重命名

SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /opt/oracle/oradata/test/archivelog
Oldest online log sequence     210
Next log sequence to archive   212
Current log sequence           212
--确认数据库是归档模式，使得数据库离线后，可以有归档日志恢复到在线状态
SQL> col name for a50
SQL> select name,file# from v$datafile;
NAME                                                    FILE#
-------------------------------------------------- ----------
/opt/oracle/oradata/test/system01.dbf                       1
/opt/oracle/oradata/test/undotbs01.dbf                      2
/opt/oracle/oradata/test/sysaux01.dbf                       3
/opt/oracle/oradata/test/users01.dbf                        4
/opt/oracle/oradata/test/user32g.dbf                        5
/opt/oracle/oradata/test/xifenfei01.dbf                     6
/opt/oracle/oradata/test/user02.dbf                         7
/opt/oracle/oradata/test/odu02.dbf                          8
/opt/oracle/oradata/test/odu01.dbf                          9
/opt/oracle/oradata/test/odu03.dbf                         10
10 rows selected.
SQL> alter tablespace xff add datafile '/opt/oracle/oradata/test/xifenfei02.chf'
   2    size 10m autoextend off;
Tablespace altered.
SQL>  select name,file# from v$datafile;
NAME                                                    FILE#
-------------------------------------------------- ----------
/opt/oracle/oradata/test/system01.dbf                       1
/opt/oracle/oradata/test/undotbs01.dbf                      2
/opt/oracle/oradata/test/sysaux01.dbf                       3
/opt/oracle/oradata/test/users01.dbf                        4
/opt/oracle/oradata/test/user32g.dbf                        5
/opt/oracle/oradata/test/xifenfei01.dbf                     6
/opt/oracle/oradata/test/user02.dbf                         7
/opt/oracle/oradata/test/odu02.dbf                          8
/opt/oracle/oradata/test/odu01.dbf                          9
/opt/oracle/oradata/test/odu03.dbf                         10
/opt/oracle/oradata/test/xifenfei02.chf                    11
11 rows selected.
SQL> create table chf.xff_test tablespace xff
  2  as
  3  select * from dba_objects;
select * from dba_objects
              *
ERROR at line 3:
ORA-01536: space quota exceeded for tablespace 'XFF'
SQL> alter user chf quota 100m on xff;
User altered.
SQL> create table chf.xff_test tablespace xff
  2  as
  3  select * from dba_objects;
Table created.
--需要重命名的数据文件内有数据，模拟数据库在生产环境中工作
SQL> alter database datafile 11 offline drop ;
Database altered.
--数据文件离线处理
SQL> !mv /opt/oracle/oradata/test/xifenfei02.chf /opt/oracle/oradata/test/xifenfei02.dbf
--系统级别把数据文件修改为正确名称
SQL> alter database rename file '/opt/oracle/oradata/test/xifenfei02.chf'
     2  to '/opt/oracle/oradata/test/xifenfei02.dbf';
Database altered.
--修改控制文件中数据文件名称
SQL> recover datafile 11;
Media recovery complete.
SQL> alter database datafile 11 online;
Database altered.
--恢复数据文件，并使其online
SQL>  select name,file# from v$datafile;
NAME                                                    FILE#
-------------------------------------------------- ----------
/opt/oracle/oradata/test/system01.dbf                       1
/opt/oracle/oradata/test/undotbs01.dbf                      2
/opt/oracle/oradata/test/sysaux01.dbf                       3
/opt/oracle/oradata/test/users01.dbf                        4
/opt/oracle/oradata/test/user32g.dbf                        5
/opt/oracle/oradata/test/xifenfei01.dbf                     6
/opt/oracle/oradata/test/user02.dbf                         7
/opt/oracle/oradata/test/odu02.dbf                          8
/opt/oracle/oradata/test/odu01.dbf                          9
/opt/oracle/oradata/test/odu03.dbf                         10
/opt/oracle/oradata/test/xifenfei02.dbf                    11
11 rows selected.

如果数据库满足以下条件，可以删除数据文件，重新添加：
1、The database must be open.
2、If a datafile is not empty, it cannot be dropped. If you must remove a datafile that is not empty and that cannot be made empty by dropping schema objects, you must drop the tablespace that contains the datafile.
3、You cannot drop the first or only datafile in a tablespace. This means that DROP DATAFILE cannot be used with a bigfile tablespace.
4、You cannot drop datafiles in a read-only tablespace.
5、You cannot drop datafiles in the SYSTEM tablespace.
6、If a datafile in a locally managed tablespace is offline, it cannot be dropped.
7、db version >= 10g R2

SQL> alter tablespace xff drop datafile 11;
alter tablespace xff drop datafile 11
*
ERROR at line 1:
ORA-03262: the file is non-empty
SQL> alter tablespace xff add datafile '/opt/oracle/oradata/test/xifenfei03.chf' size 10m autoextend off;
Tablespace altered.
SQL> alter tablespace xff drop datafile '/opt/oracle/oradata/test/xifenfei03.chf';
Tablespace altered.

oracle 修改设置密码复杂度渐增方法：
1、修改为常见密码（无特殊字符）
SQL> alter user chf identified by xifenfei;
User altered.
2、修改含一般特殊字符（如：$, %等）
SQL>
SQL> alter user chf identified by “xi%,fenfei”;
User altered.
SQL> conn chf/xi%,fenfei
Connected.
3、修改含”的特殊字符
3.1）修改制定用户密码（sys用户操作）
SQL> password chf
Changing password for chf
New password:
Retype new password:
Password changed
SQL> conn chf/aa””bb
Connected.
3.2）修改当前用户密码（需要有修改密码权限）
SQL> password
Changing password for CHF
Old password:
New password:
Retype new password:
Password changed
SQL>
注：因为一般特殊字符可以使用双引号处理，但是如果密码中含有双引号，就不能用双引号处理，可以直接使用password修改密码

[oracle@ECP-UC-DB1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Oct 17 23:37:51 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> alter user sys identified by "ab$";
User altered.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@ECP-UC-DB1 ~]$ sqlplus sys/ab$ as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Oct 17 23:38:53 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> show parameter name;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_file_name_convert                 string
db_name                              string      test
db_unique_name                       string      test
global_names                         boolean     FALSE
instance_name                        string      test
lock_name_space                      string
log_file_name_convert                string
service_names                        string      test
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@ECP-UC-DB1 ~]$ sqlplus sys/ab$abc as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Oct 17 23:39:05 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@ECP-UC-DB1 ~]$ sqlplus sys/ab$@abc as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Oct 17 23:40:06 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> show parameter name;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_file_name_convert                 string
db_name                              string      test
db_unique_name                       string      test
global_names                         boolean     FALSE
instance_name                        string      test
lock_name_space                      string
log_file_name_convert                string
service_names                        string      test
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@ECP-UC-DB1 ~]$ sqlplus sys/ab$@abc11 as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Oct 17 23:44:11 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> show parameter name;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_file_name_convert                 string
db_name                              string      test
db_unique_name                       string      test
global_names                         boolean     FALSE
instance_name                        string      test
lock_name_space                      string
log_file_name_convert                string
service_names                        string      test
SQL>  

通过以上sql发现，把sys的密码改为ab$后，无论是什么tns都可以登录数据库，而且都是本地数据库，是不是感觉很诡异，其实你仔细观察发现，密码中有了$，使得$@的操作都变成了无效的，其实就是sqlplus sys/123(随意) as sysdba方式登录本地数据库

[oracle@ECP-UC-DB1 ~]$ sqlplus sys/123 as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Mon Oct 17 23:48:23 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL>

今天参照oracle官方文档和metalink文档，对Oracle常见后台进程及其功能汇总进行了一次汇总
Oracle常见后台进程及其功能汇总
http://www.xifenfei.com/wp-content/uploads/2011/10/Oracle_Process.pdf

1、为什么要使用Startup Migrate
STARTUP MIGRATE was introduced in 9.2 as a mechanism to be sure that most everything that needs to be done to run an upgrade script or a patch script is done automatically. In the past, customers were expected to adjust certain initialization parameters prior to beginning an upgrade or applying a a patch, but most of this is now done automatically by STARTUP MIGRATE. When a customer starts a database in MIGRATE mode, the following ALTER SYSTEM commands will be set automatically:
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER SYSTEM SET “_SYSTEM_TRIG_ENABLED”=FALSE SCOPE=MEMORY;
ALTER SYSTEM SET _undo_autotune=FALSE SCOPE=MEMORY;
ALTER SYSTEM SET undo_retention=900 SCOPE=MEMORY;
ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0 SCOPE=MEMORY;
ALTER SYSTEM SET AQ_TM_PROCESSES=0 SCOPE=MEMORY;
这些我们可以从数据库的Startup Migrate命令启动数据库的日志中可以看出来

Sun Oct  9 21:53:04 2011
ALTER SYSTEM enable restricted session;
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET _system_trig_enabled=FALSE SCOPE=MEMORY;
Autotune of undo retention is turned off.
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET _undo_autotune=FALSE SCOPE=MEMORY;
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET undo_retention=900 SCOPE=MEMORY;
MMNL started with pid=12, OS id=8452
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET aq_tm_processes=0 SCOPE=MEMORY;
Sun Oct  9 21:53:04 2011
Resource Manager disabled during database migration: plan '' not set
Sun Oct  9 21:53:04 2011
ALTER SYSTEM SET resource_manager_plan='' SCOPE=MEMORY;
replication_dependency_tracking turned off (no async multimaster replication found)
Completed: ALTER DATABASE OPEN MIGRATE

2、Startup Migrate主用作用
在9i，无论升级/降级 数据库都是startup migrate
10g后增加了upgrade参数，升级可直接用startup upgrade，降级仍是startup migrate
3、Startup Migrate辅助作用（解决部分ORA-00701）

SQL> alter index I_H_OBJ#_COL# rebuild;
alter index I_H_OBJ#_COL# rebuild
*
ERROR at line 1:
ORA-00701: object necessary for warmstarting database cannot be altered
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup migrate;
ORACLE instance started.
Total System Global Area 139531744 bytes
Fixed Size 452064 bytes
Variable Size 121634816 bytes
Database Buffers 16777216 bytes
Redo Buffers 667648 bytes
Database mounted.
Database opened.
SQL> alter index I_H_OBJ#_COL# rebuild;
Index altered.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 139531744 bytes
Fixed Size 452064 bytes
Variable Size 121634816 bytes
Database Buffers 16777216 bytes
Redo Buffers 667648 bytes
Database mounted.
Database opened.

1、sqlplus显示语言设置
export NLS_LANG=”AMERICAN_AMERICA.ZHS16GBK”
export NLS_LANG=”SIMPLIFIED CHINESE_CHINA.ZHS16GBK”
注意数据库编码：ZHS16GBK/UTF8
2、dbms_output.put_line显示最前面空格
SQL> set serveroutput on
SQL> exec dbms_output.put_line(‘     abc’);
abc
PL/SQL procedure successfully completed.
SQL> set serveroutput on format wrapped
SQL> exec dbms_output.put_line(‘   abc’);
   abc
PL/SQL procedure successfully completed.
3、sqlplus 语句中间查询对象结构
SQL> select owner
2 # desc input
Name Null? Type
—————————————– ——– —————————-
OWNER VARCHAR2(30)
OBJECT_NAME VARCHAR2(30)
SUBOBJECT_NAME VARCHAR2(30)
OBJECT_ID NUMBER
DATA_OBJECT_ID NUMBER
OBJECT_TYPE VARCHAR2(19)
CREATED DATE
LAST_DDL_TIME DATE
TIMESTAMP VARCHAR2(19)
STATUS VARCHAR2(7)
TEMPORARY VARCHAR2(1)
GENERATED VARCHAR2(1)
SECONDARY VARCHAR2(1)
2 ,status from input where rownum<10;
no rows selected
下一行以#开头, 就可以执行一条sql*plus命令, 执行完后, 刚才的语句可以继续输入
4、Sql*plus中sql语句中间有空行
SQL> select owner
2
SQL> ,status from input where rownum<10; SP2-0734: unknown command beginning “,status fr…” – rest of line ignored. 原因是sqlplus遇到空行就认为是语句结束了. 其实要改变这种现象, 只要使用SQLBLANKLINES参数就可以了 SQL> SET SQLBLANKLINES ON
SQL> select owner
2
3 ,status from input where rownum<10;
no rows selected

一、为什么需要System checkpoint SCN号与Datafile Checkpoint SCN号
1.对只读表空间，其数据文件的Datafile Checkpoint SCN、Start SCN和END SCN号均相同。这三个SCN在表空间处于只读期间都将被冻结。
2.如果控制文件不是当前的控制文件，则System checkpoint会小于Start SCN或END SCN号。记录这些SCN号，可以区分控制文件是否是当前的控制文件。
Recovery database using backup controlfile
当有一个Start SCN号超过了System Checkpoit SCN号时，则说明控制文件不是当前的控制文件，因此在做recovery时需要采用using backup controlfile。这是为什么需要记录SystemCheckpoint SCN的原因之一。
二、重建控制文件，重建方式分两种（resetlogs和noresetlogs）
1.使用resetlogs选项时，System Checkpoint SCN为被归为0，而其中记录的各个数据文件的Datafile Checkpoint SCN则来自于Start SCN（也就是说可能会从冷备份的数据文件的数据文件头中获取）。根据上述的描述，此时需要采用using backup controlfile做recovery.因此情况是System Checkpoint SCN=0 < Start SCN = Datafile Checkpoint SCN。 2.使用noresetlogs选项时，有一个前提就是：一定要有online redo log的存在。否则就要使用resetlogs选项。这个时候控制文件重建好时，其system checkpoint SCN=Datafile Checkpoint SCN=Lastest Checkpoint SCN in online redo log,我们可以看到Datafile Checkpoint SCN并没有从Start SCN中读取。而是读取了最新的日志文件中的SCN作为自己的数据。此时重建的控制文件在恢复中的作用跟最新的控制文件类似，System Checkpoint SCN(已经读取最新的redo log的checkpoint SCN信息)可能会>Start SCN（因为数据文件可能会从冷备份中恢复），恢复时就不需要加using backup controlfile子句了。
3.关于backup controlfile的补充：backup controlfile只有备份时刻的archive log信息，并没有DB crash时刻的archive log信息，所以并不会自动应用online redo log,而是提示找不到序号为Lastest Archive log sequence + 1的archive log,尽管你可以手动指定online redo log来实现完全恢复，但因为一旦使用了using backup controlfile子句，Oracle就视为不完全恢复，必须open resetlogs!实际上，假如你有旧的控制文件又不想resetlogs，那很简单，使用旧的控制文件mount然后backup to trace，然后手工创建控制文件，使用reuse database … noresetlogs .这样就可以recover database自动恢复并open database而不用resetlogs了(记住：必须有所有的online redo logs才可以这样！)。
三、Low SCN与Next SCN
1.在一个事务提交后，会在redo log中存在一条redo记录，同时，系统为其提供一个最新的SCN（通过函数dbms_flashback.get_system_change_number可以知道当前的最新SCN），记录在该条记录中。如果该条记录是在redo log被清空（日志满做切换时或发生checkpoint时，所有变化日志已经被写入数据文件中）前，则其SCN被记录为redo log的low SCN。以后在日志再次被清空前写入的redo记录中SCN则成为Next SCN。
2.当日志切换或发生checkpoint时，从Low SCN到Next SCN之间的所有redo记录的数据就被DBWn进程写入数据文件中，而CKPT进程则将所有数据文件（无论redo log中的数据是否影响到该数据文件）的文件头上记录的Start SCN(通过视图v$datafile_header的字段checkpoint_change#可以查询)更新为Next SCN，同时将控制文件中的System Checkpoint SCN（通过视图v$database的字段checkpoint_change#可以查询）、每个数据文件对应的Datafile Checkpoint（通过视图v$datafile的字段checkpoint_change#可以查询）也更新为Next SCN。但是，如果该数据文件所在的表空间被设置为read-only时，数据文件的Start SCN和控制文件中Datafile Checkpoint SCN都不会被更新。
其他请见：SCN与Oracle数据库恢复的关系

在9i和以前的版本，索引提示的格式为/*+ index(table_alias) */或/*+ index(table_alias index_name) */，但是在10g中不仅可以通过索引名称来确定HINT的索引，还可以通过指定列名的方式，格式为/*+ index(table_alias (column_names)) */

SQL> create table test_hint
  2  as
  3  select * from dba_objects;
Table created.
SQL> create index ind_hint on test_hint(owner,object_type);
Index created.
SQL>  exec dbms_stats.gather_table_stats(user, 'TEST_HINT',
  2   method_opt => 'for all indexed columns size 100',cascade=>true);
PL/SQL procedure successfully completed.
SQL> set autot trace exp
SQL> select * from test_hint where owner = 'SYS';
Execution Plan
----------------------------------------------------------
Plan hash value: 11101196
-------------------------------------------------------------------------------
| Id  | Operation         | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |           | 23272 |  2113K|   161   (1)| 00:00:02 |
|*  1 |  TABLE ACCESS FULL| TEST_HINT | 23272 |  2113K|   161   (1)| 00:00:02 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("OWNER"='SYS')
SQL> select /*+index(a)*/ * from test_hint  a where owner = 'SYS';
Execution Plan
----------------------------------------------------------
Plan hash value: 890897193
-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           | 23272 |  2113K|  1122   (1)| 00:00:14 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HINT | 23272 |  2113K|  1122   (1)| 00:00:14 |
|*  2 |   INDEX RANGE SCAN          | IND_HINT  | 23272 |       |    84   (0)| 00:00:02 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OWNER"='SYS')
SQL> select /*+index(a ind_hint)*/ * from test_hint  a where owner = 'SYS';
Execution Plan
----------------------------------------------------------
Plan hash value: 890897193
-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           | 23272 |  2113K|  1122   (1)| 00:00:14 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HINT | 23272 |  2113K|  1122   (1)| 00:00:14 |
|*  2 |   INDEX RANGE SCAN          | IND_HINT  | 23272 |       |    84   (0)| 00:00:02 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OWNER"='SYS')
SQL> select /*+index(a (owner,object_type))*/ * from test_hint  a where owner = 'SYS';
Execution Plan
----------------------------------------------------------
Plan hash value: 890897193
-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           | 23272 |  2113K|  1122   (1)| 00:00:14 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HINT | 23272 |  2113K|  1122   (1)| 00:00:14 |
|*  2 |   INDEX RANGE SCAN          | IND_HINT  | 23272 |       |    84   (0)| 00:00:02 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OWNER"='SYS')
--指定和index完全一致的列，走index
SQL> select /*+index(a (owner))*/ * from test_hint  a where owner = 'SYS';
Execution Plan
----------------------------------------------------------
Plan hash value: 890897193
-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           | 23272 |  2113K|  1122   (1)| 00:00:14 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HINT | 23272 |  2113K|  1122   (1)| 00:00:14 |
|*  2 |   INDEX RANGE SCAN          | IND_HINT  | 23272 |       |    84   (0)| 00:00:02 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OWNER"='SYS')
--指定列和where条件一致，也可以使用该index
SQL> select /*+index(a (object_id))*/ * from test_hint  a where owner = 'SYS';
Execution Plan
----------------------------------------------------------
Plan hash value: 11101196
-------------------------------------------------------------------------------
| Id  | Operation         | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |           | 23272 |  2113K|   161   (1)| 00:00:02 |
|*  1 |  TABLE ACCESS FULL| TEST_HINT | 23272 |  2113K|   161   (1)| 00:00:02 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("OWNER"='SYS')
--虽然是index中的一个列，但是由于不是where条件中，所以不能被使用
SQL> select /*+index(a (owner))*/ * from test_hint  a where object_type = 'TABLE';
Execution Plan
----------------------------------------------------------
Plan hash value: 1755360976
-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |  1752 |   159K|   104   (0)| 00:00:02 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_HINT |  1752 |   159K|   104   (0)| 00:00:02 |
|*  2 |   INDEX SKIP SCAN           | IND_HINT  |  1752 |       |    25   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_TYPE"='TABLE')
       filter("OBJECT_TYPE"='TABLE')
--指定index的第一列，虽然不在where中，但是还是会使用index
--说明：使用/*+ index(table_alias (column_names)) */方式的hint，需要先测试，有可能不能达到预期效果

TOM写了个好工具SHOW_SPACE,这个工具对于Oracle来讲其实就是个存储过程，这个存储过程可以用来分析空间使用情况，有了此工具，就不用再通过写SQL语句来看每条记录或表占用表空间的大小了，使用起来很方便。

create or replace procedure show_space
( p_segname_1 in varchar2,
p_owner_1 in varchar2 default user,
p_type_1 in varchar2 default 'TABLE',
p_space in varchar2 default 'AUTO',
p_analyzed in varchar2 default 'Y'
)
as
p_segname varchar2(100);
p_type varchar2(10);
p_owner varchar2(30);
l_unformatted_blocks number;
l_unformatted_bytes number;
l_fs1_blocks number;
l_fs1_bytes number;
l_fs2_blocks number;
l_fs2_bytes number;
l_fs3_blocks number;
l_fs3_bytes number;
l_fs4_blocks number;
l_fs4_bytes number;
l_full_blocks number;
l_full_bytes number;
l_free_blks number;
l_total_blocks number;
l_total_bytes number;
l_unused_blocks number;
l_unused_bytes number;
l_LastUsedExtFileId number;
l_LastUsedExtBlockId number;
l_LAST_USED_BLOCK number;
procedure p( p_label in varchar2, p_num in number )
is
begin
dbms_output.put_line( rpad(p_label,40,'.') ||
p_num );
end;
begin
p_segname := upper(p_segname_1); -- rainy changed
p_owner := upper(p_owner_1);
p_type := p_type_1;
if (p_type_1 = 'i' or p_type_1 = 'I') then --rainy changed
p_type := 'INDEX';
end if;
if (p_type_1 = 't' or p_type_1 = 'T') then --rainy changed
p_type := 'TABLE';
end if;
if (p_type_1 = 'c' or p_type_1 = 'C') then --rainy changed
p_type := 'CLUSTER';
end if;
dbms_space.unused_space
( segment_owner => p_owner,
segment_name => p_segname,
segment_type => p_type,
total_blocks => l_total_blocks,
total_bytes => l_total_bytes,
unused_blocks => l_unused_blocks,
unused_bytes => l_unused_bytes,
LAST_USED_EXTENT_FILE_ID => l_LastUsedExtFileId,
LAST_USED_EXTENT_BLOCK_ID => l_LastUsedExtBlockId,
LAST_USED_BLOCK => l_LAST_USED_BLOCK );
if p_space = 'MANUAL' or (p_space <> 'auto' and p_space <> 'AUTO') then
dbms_space.free_blocks
( segment_owner => p_owner,
segment_name => p_segname,
segment_type => p_type,
freelist_group_id => 0,
free_blks => l_free_blks );
p( 'Free Blocks', l_free_blks );
end if;
p( 'Total Blocks', l_total_blocks );
p( 'Total Bytes', l_total_bytes );
p( 'Unused Blocks', l_unused_blocks );
p( 'Unused Bytes', l_unused_bytes );
p( 'Last Used Ext FileId', l_LastUsedExtFileId );
p( 'Last Used Ext BlockId', l_LastUsedExtBlockId );
p( 'Last Used Block', l_LAST_USED_BLOCK );
/*IF the segment is analyzed */
if p_analyzed = 'Y' then
dbms_space.space_usage(segment_owner => p_owner ,
segment_name => p_segname ,
segment_type => p_type ,
unformatted_blocks => l_unformatted_blocks ,
unformatted_bytes => l_unformatted_bytes,
fs1_blocks => l_fs1_blocks,
fs1_bytes => l_fs1_bytes ,
fs2_blocks => l_fs2_blocks,
fs2_bytes => l_fs2_bytes,
fs3_blocks => l_fs3_blocks ,
fs3_bytes => l_fs3_bytes,
fs4_blocks => l_fs4_blocks,
fs4_bytes => l_fs4_bytes,
full_blocks => l_full_blocks,
full_bytes => l_full_bytes);
dbms_output.put_line(rpad(' ',50,'*'));
dbms_output.put_line('The segment is analyzed');
p( '0% -- 25% free space blocks', l_fs1_blocks);
p( '0% -- 25% free space bytes', l_fs1_bytes);
p( '25% -- 50% free space blocks', l_fs2_blocks);
p( '25% -- 50% free space bytes', l_fs2_bytes);
p( '50% -- 75% free space blocks', l_fs3_blocks);
p( '50% -- 75% free space bytes', l_fs3_bytes);
p( '75% -- 100% free space blocks', l_fs4_blocks);
p( '75% -- 100% free space bytes', l_fs4_bytes);
p( 'Unused Blocks', l_unformatted_blocks );
p( 'Unused Bytes', l_unformatted_bytes );
p( 'Total Blocks', l_full_blocks);
p( 'Total bytes', l_full_bytes);
end if;
end;
/

用法

SQL> create table t
  2  as
  3  select * from dba_objects;
Table created.
SQL> set serverout on
SQL>  exec show_space('T','TEST');
Total Blocks............................768
Total Bytes.............................6291456
Unused Blocks...........................52
Unused Bytes............................425984
Last Used Ext FileId....................4
Last Used Ext BlockId...................1033
Last Used Block.........................76
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............0
25% -- 50% free space bytes.............0
50% -- 75% free space blocks............0
50% -- 75% free space bytes.............0
75% -- 100% free space blocks...........0
75% -- 100% free space bytes............0
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................696
Total bytes.............................5701632
PL/SQL procedure successfully completed.
SQL> delete from t;
50602 rows deleted.
SQL> exec show_space('T','TEST');
Total Blocks............................768
Total Bytes.............................6291456
Unused Blocks...........................52
Unused Bytes............................425984
Last Used Ext FileId....................4
Last Used Ext BlockId...................1033
Last Used Block.........................76
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............0
25% -- 50% free space bytes.............0
50% -- 75% free space blocks............0
50% -- 75% free space bytes.............0
75% -- 100% free space blocks...........696
75% -- 100% free space bytes............5701632
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................0
Total bytes.............................0
PL/SQL procedure successfully completed.
SQL> alter table t move;
Table altered.
SQL> exec show_space('T','TEST');
Total Blocks............................8
Total Bytes.............................65536
Unused Blocks...........................5
Unused Bytes............................40960
Last Used Ext FileId....................4
Last Used Ext BlockId...................401
Last Used Block.........................3
*************************************************
The segment is analyzed
0% -- 25% free space blocks.............0
0% -- 25% free space bytes..............0
25% -- 50% free space blocks............0
25% -- 50% free space bytes.............0
50% -- 75% free space blocks............0
50% -- 75% free space bytes.............0
75% -- 100% free space blocks...........0
75% -- 100% free space bytes............0
Unused Blocks...........................0
Unused Bytes............................0
Total Blocks............................0
Total bytes.............................0
PL/SQL procedure successfully completed.

今天遇到一个比较特殊的死锁现象，记录下来

DEADLOCK DETECTED ( ORA-00060 )
[Transaction Deadlock]
The following deadlock is not an ORACLE error. It is a
deadlock due to user error in the design of an application
or from issuing incorrect ad-hoc SQL. The following
information may aid in determining the deadlock:
Deadlock graph:
                       ---------Blocker(s)--------  ---------Waiter(s)---------
Resource Name          process session holds waits  process session holds waits
TX-00090022-000002ba        15     145     X             15     145           X
session 145: DID 0001-000F-00000019     session 145: DID 0001-000F-00000019
Rows waited on:
Session 145: obj - rowid = 0000E0A3 - AAAOCjAAFAAAAA8AAA
  (dictionary objn - 57507, file - 5, block - 60, slot - 0)
Information on the OTHER waiting sessions:
End of information on OTHER waiting sessions.
Current SQL statement for this session:
UPDATE T SET Y = Y WHERE X = :B1
----- PL/SQL Call Stack -----
  object      line  object
  handle    number  name
0x67987910         4  CHF.T
===================================================

问题原因：自治事件导致(重现)

drop table t;
create table t ( x int, y int );
create or replace trigger t before update on t
for each row
declare
    pragma autonomous_transaction;
begin
    update t set y = y where x = :new.x;
    commit;
end;
/
insert into t values ( 1, 1 );
commit;
update t set y = y where x = 1;