Oracle Tablespace Read-Only Oracle Tips by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Features for the Data Warehouse
After we have packed the row data and the indexes within their respective tablespace, we can now alter the tablespaces to make them read-only. Once the tablespace has been altered to become read-only, a single backup can be used for all future recovery. Unlike ordinary tablespaces, online backups never need to issue the ALTER TABLESPACE FACT_96 BEGIN BACKUP commands. During startup of an Oracle instance, Oracle verifies that a tablespace is in read-only mode and recognizes that it does not need any media recovery. In short, a recovery of an Oracle data warehouse will only consist of applying the redo logs against those tablespaces that were in update mode. This greatly simplifies database recovery for a very large Oracle warehouse. This technique also allows a tablespace to avoid the time consuming overhead of writing to the online redo logs since roll-forward operations are performed by re-running the nightly update routines. In addition read-only tablespaces will never write to the database file headers, saving system I/O.

With Oracle version 7.1 and above, any Oracle tablespace may be made read-only by issuing the alter tablespace command.

SVRMGRL > shutdown;

SVRMGRL > startup restrict;

SVRMGRL > alter tablespace warehouse_one read only;

SVRMGRL > alter database open;

Note: In order to change the status of a tablespace, the Oracle database must be quiesced. That is, there must be no active transactions running against the tablespace at the time that the alter tablespace command is issued. In the above example, we have shutdown Oracle and started in database in restricted mode.

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