OMF管理的文件会自动删除
有一点经验的DBA都会记得，drop tablespace的时候，如果没有带including contents and datafiles的字句，数据文件是不会被删除的，上周周日演示，drop tablespace时，数据文件被自动删除了，当时我给的解释是，文件是空的，没有使用过，才会出现这种情况，翻回文档才发现，其实是因为，该文件是OMF的。
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[oracle@nobody admin]$ rlwrap sqlplus / as sysdba
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SQL*Plus: Release 11.2.0.1.0 Production on Mon Jun 24 05:44:20 2013
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Copyright (c) 1982, 2009, Oracle. All rights reserved.
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Connected to:
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Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
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With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
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Data Mining and Real Application Testing options
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nobody@TESTDB>show parameter create;
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NAME TYPE VALUE
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------------------------------------ ----------- ------------------------------
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create_bitmap_area_size integer 8388608
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create_stored_outlines string
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db_create_file_dest string +DATA
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db_create_online_log_dest_1 string
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db_create_online_log_dest_2 string
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db_create_online_log_dest_3 string
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db_create_online_log_dest_4 string
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db_create_online_log_dest_5 string
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nobody@TESTDB>alter system set db_create_file_dest='/u01/app/oracle/oradata/testdb';
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System altered.
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nobody@TESTDB>create tablespace omf_tbs datafile size 10m;
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Tablespace created.
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nobody@TESTDB>create tablespace no_omf_tbs datafile '/u01/app/oracle/oradata/testdb/no_omf_tbs01.dbf' size 10m;
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Tablespace created.
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nobody@TESTDB>select d.name from v$datafile d, v$tablespace t where d.ts# = t.ts# and t.name in ('OMF_TBS','NO_OMF_TBS');
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NAME
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--------------------------------------------------------------------------------------------------------------------------------------------
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/u01/app/oracle/oradata/testdb/HUA01/datafile/o1_mf_omf_tbs_8wgv3shj_.dbf
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/u01/app/oracle/oradata/testdb/no_omf_tbs01.dbf
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nobody@TESTDB>host ls -l /u01/app/oracle/oradata/testdb/HUA01/datafile/o1_mf_omf_tbs_8wgv3shj_.dbf
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-rw-r----- 1 oracle asmadmin 10493952 Jun 24 05:45 /u01/app/oracle/oradata/testdb/HUA01/datafile/o1_mf_omf_tbs_8wgv3shj_.dbf
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nobody@TESTDB>host ls -l /u01/app/oracle/oradata/testdb/no_omf_tbs01.dbf
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-rw-r----- 1 oracle asmadmin 10493952 Jun 24 05:45 /u01/app/oracle/oradata/testdb/no_omf_tbs01.dbf
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nobody@TESTDB>drop tablespace omf_tbs;
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Tablespace dropped.
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nobody@TESTDB>host ls -l /u01/app/oracle/oradata/testdb/HUA01/datafile/o1_mf_omf_tbs_8wgv3shj_.dbf
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ls: /u01/app/oracle/oradata/testdb/HUA01/datafile/o1_mf_omf_tbs_8wgv3shj_.dbf: No such file or directory
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nobody@TESTDB>drop tablespace no_omf_tbs;
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Tablespace dropped.
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nobody@TESTDB>host ls -l /u01/app/oracle/oradata/testdb/no_omf_tbs01.dbf
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-rw-r----- 1 oracle asmadmin 10493952 Jun 24 06:14 /u01/app/oracle/oradata/testdb/no_omf_tbs01.dbf
Performance Tuning Guide 中对于 OMF 的描述中对此有解析。
When file systems can contain all Oracle Database data, database administration is simplified by using Oracle Managed Files. Oracle Database internally uses standard file system interfaces to create and delete files as needed for tablespaces, temp files, online logs, and control files. Administrators only specify the file system directory to be used for a particular type of file. You can specify one default location for data files and up to five multiplexed locations for the control and online redo log files. Oracle Database ensures that a unique file is created and then deleted when it is no longer needed. This reduces corruption caused by administrators specifying the wrong file, reduces wasted disk space consumed by obsolete files, and simplifies creation of test and development databases.
