| smon and instance recovery [message #331719] |
Fri, 04 July 2008 23:43  |
varu123
Messages: 754
Registered: October 2007
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Senior Member |
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During startup,SMON performs instance recovery.
It applies the redo. My question is does it apply the redo directly to datafiles or in the buffer cache thus generating the dirty blocks that are written by DBWR?
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| Re: smon and instance recovery [message #331849 is a reply to message #331719] |
Sun, 06 July 2008 01:01  |
varu123
Messages: 754
Registered: October 2007
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Senior Member |
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Upon every instance startup SMON checks the SCN in the datafiles headers and in the control file headers for any inconsistency.
In the case of instance/crash recovery,it applies redo.
But Does it applies the redo directly in the datafiles bypassing buffer cache or first in buffer cache and from there DBWR finishes the job?
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| Re: smon and instance recovery [message #337721 is a reply to message #333734] |
Thu, 31 July 2008 18:54 |
sunil_v_mishra
Messages: 506
Registered: March 2005
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Senior Member |
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Instance and crash recovery are the automatic application of redo log to records Oracle data blocks after a crash or system failure. During normal operation, if an instance is shut down cleanly (as when using a SHUTDOWN IMMEDIATE statement), rather than terminated abnormally, then the in-memory changes that have not already been written to the datafiles on disk are written to disk as part of the checkpoint performed during shutdown.
However, if a single instance database crashes or if all instances of an Oracle Real Application Cluster configuration crash, then Oracle performs crash recovery at the next startup. If one or more instances of an Oracle Real Application Cluster configuration crash, then a surviving instance performs instance recovery automatically. Instance and crash recovery occur in two steps: cache recovery followed by transaction recovery.
The database can be opened as soon as cache recovery completes, so improving the performance of cache recovery is important for increasing availability.
1. What is cache recovery?
Cache Recovery (Rolling Forward)
During the cache recovery step, Oracle applies all committed and uncommitted changes in the redo log files to the affected data blocks. The work required for cache recovery processing is proportional to the rate of change to the database (update transactions each second) and the time between checkpoints.
3. What is transaction recovery?
Transaction Recovery (Rolling Back)
To make the database consistent, the changes that were not committed at the time of the crash must be undone (in other words, rolled back). During the transaction recovery step, Oracle applies the rollback segments to undo the uncommitted changes.
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| Re: smon and instance recovery [message #338100 is a reply to message #338068] |
Sun, 03 August 2008 10:08 |
sunil_v_mishra
Messages: 506
Registered: March 2005
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Senior Member |
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Michel I feel Its your assumption that original poster wants to read more, because if he wants to read more he would not ask specific question on orafaq...  ..
When people ask any question on orafaq they are interested just answer to there question nothing more than that, they all know there is documentation and metalink, they need answer to the point of
their question
And personally i don't want OP to read more. If he/she want to read more than read documentation and if they do have right then can see metalink ...why do they come on orafaq  ?
Can you tell me who had written oracle documentation ?
For Most of question asked on orafaq you can give some link of oracle documentation or metalink
[Updated on: Sun, 03 August 2008 10:12] Report message to a moderator |
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