do we loss any transactions that are still resided in the log buffer? what is the actual role for log buffer?
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do we loss any transactions that are still resided in the log buffer? what is the actual role for log buffer?
At what/which stage?
Sam
say... shutdown abort or system power down without notice
Yes. All uncommitted transactions will be lost.
Any transaction is not a complete untill the value from buffer goes into the redo log files, Once it is there into the redo log files it can'nt be lost. So there is no question of loss of data in a transaction which is still under log buffer.
Not quite precise enough! Even when a change is written into a redo log file it will be lost in case of instance crash, if it has not been commited yet. In the process of instance recovery such a change will be rolled back.Quote:
Originally posted by anujdutt
Any transaction is not a complete untill the value from buffer goes into the redo log files, Once it is there into the redo log files it can'nt be lost. So there is no question of loss of data in a transaction which is still under log buffer.
Raminder's answer was totaly exact - all uncomitted transactions will be loss in a case of instance failure, no matter if they have been written in a redo log file or not.
then... would it be a chance that committed transactions are still left in the buffer and got an instance crash?
No, before the transaction is commited all its changes must be written to redolog files on disk, so there is no chance of loosing any commited transaction (that is, if nothing is preventing the crash or media recovery to succeed, but that is another story).