The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion.
Redo logs records all the changes to the database whether commited or uncommited. How does it know whether you are committing or rolling back till you commit it. Oracle always thinks positively that everything is going to be commited and writes to the log and when it is rolled back, it rolls back from the rollback segment otherwise those segments will be used for another transactions. Please correct me if iam wrong.
The online redolog is a set of minimum two filegroups which has minimum one member and oracle uses it to record all the changes made to the database whether it is commited or not commited.oracle uses it to perform recovery after database crash.
Online Redo Log files are those which contain the information that changed the datafile it contains both the commited and uncommited data aswell. These files are needed for recovery.
Redo logs records all the changes to the database whether commited or uncommited. How does it know whether you are committing or rolling back till you commit it. Oracle always thinks positively that everything is going to be commited and writes to the log and when it is rolled back it rolls back from the rollback segment otherwise those segments will be used for another transactions. Please correct me if iam wrong.
Online redologs name is used since archivelogs are called offline redologs. Online redologs can be in three states current to which lWr is currently writing transaction changes then this current becomes active after it gets filled and logswitch/ckpt happens then active becomes inactive only after its contents are syncronized with corresponding datafiles and undo files after this step it becomes inactive and it can go to current state only from inactive mode since this is a cycle its called cyclic buffer.
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