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| Re: hotbackup taking tablespace offline [message #118187 is a reply to message #118180] |
Tue, 03 May 2005 09:46   |
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Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille
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Senior Member
Account Moderator |
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Most frequently asked question.
The tablespace doesnt get offline.
Records are still being inserted into tablespace.
There are some concerns here.
----------- from an article by Tim Gorman -------
When the ALTER TABLESPACE ... BEGIN BACKUP command is issued, a global
database checkpoint occurs. This means that the current system change number (SCN) is
logged to the redo log stream in a checkpoint record, and all buffers in the Buffer Cache
modified prior to that SCN must be flushed down to the datafiles. Once the checkpoint
completes, then the header block of each datafile in the tablespace is frozen, meaning that the
header will not be updated to record the SCN of future checkpoints.
However, the writing of database blocks to the body of the datafiles is
not changed in any way. During future checkpoints, while the tablespace remains in
backup mode, blocks continue to be written to the datafiles, just like normal. When
the DBWR process flushes blocks to the datafiles outside of checkpoint processing, this
continues in the datafiles belonging to the tablespace being backed up, just like
normal. Meanwhile, while this normal I/O occurs to and from the tablespace in
backup mode, some type of operating-system utility is copying the datafiles, backing
them up. This utility, which on UNIX might be the dd, cp, tar, cpio, or dump
commands, is actually backing up datafiles that are in flux. The files are being changed, as
they are being saved to backup media. To put it another way, the datafiles that are being
backed up are not consistent, and in one sense of the word, are corrupted.
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| Re: hotbackup taking tablespace offline [message #118459 is a reply to message #118452] |
Thu, 05 May 2005 07:28 |
sunil_v_mishra
Messages: 506
Registered: March 2005
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Senior Member |
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Hi,
Check out below written thinks you will better understand this.... author of this answer is frank naude i m just posting it on forum so that other can see it and can get knowledge releated to it
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Does Oracle write to data files in begin/hot backup mode?
Oracle will stop updating file headers, but will continue to write data to the database files even if a tablespace is in backup mode.
In backup mode, Oracle will write out complete changed blocks to the redo log files. Normally only deltas (changes) are logged to the redo logs. This is done to enable reconstruction of a block if only half of it was backed up (split blocks). Because of this, one should notice increased log activity and archiving during on-line backups.
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friend
sunil
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