| hot backup [message #149393] |
Thu, 01 December 2005 08:02  |
risy_s
Messages: 44
Registered: September 2005
Location: Mumbai
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Member |
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hi all
i need some tips on hot backup...as i know when v put a TS in hot backup mode scn marker is frozen and whole image of block is written to the redolog instade or writing only changes....
so in the case of recovery oracle recover data from redo log file....
but in normal case.. i mean if u didnt take a hot backup of some TS in that case redo log also contain changes....
so from there v can recover it
so why v need a hot backup...??? so plz tell me what happens exectly during hot backu..? wher it is backedup n how ???
Thank you
risy....
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| Re: hot backup [message #149622 is a reply to message #149393] |
Fri, 02 December 2005 08:49  |
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Mahesh Rajendran
Messages: 10707
Registered: March 2002
Location: oracleDocoVille
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Senior Member
Account Moderator |
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>> so why v need a hot backup...???
USE RMAN.
Say no to ALTER TABLESPACE xxx BEGIN BACKUP.
>> ? so plz tell me what happens exectly during hot backu..?
Quoting Tim Gorman
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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: hot backup [message #168182 is a reply to message #149622] |
Wed, 19 April 2006 03:55 |
hexmanju
Messages: 78
Registered: September 2005
Location: MUMBAI
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Member |
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Yes Mahesh Please Throw light on it...As to what happens when you copy the files to a sperate location during Hot Backup and then issue the end Backup Command....
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