Re: Undocumented Instance/Media Recover Feature?
- From: Tim Johnston <tjohnston@xxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 26 May 2004 14:06:24 -0400
Oracle didn't create that segment in the datafile... The segment that
used to exist in the old datafile is still referenced in the data
dictionary... However, the actually physical segment does not exist in
the "MISSING" file... Here's another example...
First I create the tablespace and put a table in it...
$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.3.0 - Production on Wed May 26 13:50:34 2004
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.3.0 - Production
With the Partitioning option
JServer Release 9.2.0.3.0 - Production
SQL> create tablespace tim datafile '/export/home/oradata/PV429/tim.dbf'
size 10M;
Tablespace created.
SQL>
SQL> create table tim_table ( col1 number ) tablespace tim;
Table created.
SQL> insert into tim_table values (1);
1 row created.
SQL> commit;
Commit complete.
SQL> alter database backup controlfile to trace;
Database altered.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.3.0 - Production
With the Partitioning option
JServer Release 9.2.0.3.0 - Production
$
Then I edit the control file create and recreate the controlfiles...
$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.3.0 - Production on Wed May 26 13:58:03 2004
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to an idle instance.
SQL> startup nomount
ORACLE instance started.
Total System Global Area 252793548 bytes
Fixed Size 455372 bytes
Variable Size 167772160 bytes
Database Buffers 83886080 bytes
Redo Buffers 679936 bytes
SQL> @cre_control
Control file created.
SQL> alter database open;
Database altered.
SQL> set pagesize 1000
SQL> select * from dba_data_files where tablespace_name = 'TIM';
FILE_NAME
--------------------------------------------------------------------------------
FILE_ID TABLESPACE_NAME BYTES BLOCKS STATUS
---------- ------------------------------ ---------- ---------- ---------
RELATIVE_FNO AUT MAXBYTES MAXBLOCKS INCREMENT_BY USER_BYTES USER_BLOCKS
------------ --- ---------- ---------- ------------ ---------- -----------
/opt/oracle/product/9.2.0/dbs/MISSING00035
35 TIM AVAILABLE
35
Now you notice that dba_segments shows this table exists in the
tablespace with the "MISSING" datafile...
SQL> select * from dba_segments where tablespace_name = 'TIM';
OWNER
------------------------------
SEGMENT_NAME
--------------------------------------------------------------------------------
PARTITION_NAME SEGMENT_TYPE TABLESPACE_NAME
------------------------------ ------------------
------------------------------
HEADER_FILE HEADER_BLOCK BYTES BLOCKS EXTENTS INITIAL_EXTENT
----------- ------------ ---------- ---------- ---------- --------------
NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS PCT_INCREASE FREELISTS FREELIST_GROUPS
----------- ----------- ----------- ------------ ---------- ---------------
RELATIVE_FNO BUFFER_
------------ -------
SYS
TIM_TABLE
TABLE TIM
35 5 65536
1 2147483645 1 1
35 DEFAULT
However, if you try to access the segment, you get an error...
SQL> select * from tim_table;
select * from tim_table
*
ERROR at line 1:
ORA-00376: file 35 cannot be read at this time
ORA-01111: name for data file 35 is unknown - rename to correct file
ORA-01110: data file 35: '/opt/oracle/product/9.2.0/dbs/MISSING00035'
And if you look in v$datafile you notice the status is "RECOVER"... The
segment doesn't really exist in your database...
SQL> select * from v$datafile where file# = 35;
FILE# CREATION_CHANGE# CREATION_ TS# RFILE# STATUS ENABLED
---------- ---------------- --------- ---------- ---------- -------
----------
CHECKPOINT_CHANGE# CHECKPOIN UNRECOVERABLE_CHANGE# UNRECOVER LAST_CHANGE#
------------------ --------- --------------------- --------- ------------
LAST_TIME OFFLINE_CHANGE# ONLINE_CHANGE# ONLINE_TI BYTES BLOCKS
--------- --------------- -------------- --------- ---------- ----------
CREATE_BYTES BLOCK_SIZE
------------ ----------
NAME
--------------------------------------------------------------------------------
PLUGGED_IN BLOCK1_OFFSET
---------- -------------
AUX_NAME
--------------------------------------------------------------------------------
35 1421140 45 35 *RECOVER*
READ WRITE
0 0 1421349
26-MAY-04 0 0 0 0
0 16384
/opt/oracle/product/9.2.0/dbs/MISSING00035
0 4294967295
UNKNOWN
SQL>
As far as how it gets out of sync, I have seen this a couple times...
In my case, it was when I encountered an ORA-600 during a DDL
operation... i.e. During a drop tablespace...
Tim
Orr, Steve wrote:
>The curiousity is that the file didn't exist in the O/S, Oracle created
>it without telling me, and it created and placed a database object into
>that file, again, without telling me. I just stumbled across this but
>I'd like to KNOW when this happens.
>
>V$DATAFILE and V$TABLESPACE get information from the control file so how
>could they be out of sync?=20
>
>
>
>
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