The Redo Log Buffer
The redo log buffer is a RAM area (defined by the
initialization parameter log_buffer) that works to save changes to data, in case
something fails and Oracle has to put it back into its original state (a
“rollback”). When Oracle SQL updates a table (a process called Data
Manipulation Language, or DML), redo images are created and stored in the redo
log buffer. Since RAM is faster than disk, this makes the storage of redo very
fast.
Also see my notes on
sizing the redo log buffer.
The Oracle redo log buffer provides the following functions
within the Oracle SGA:
- Serves for assistance with database recovery tasks
- Records all changes made to database blocks
- Places changes recorded to redo entries for redo logs
The database initialization parameter log_buffer defines the
default size of the redo log buffer within Oracle 11g.
Oracle will eventually flush the redo log buffer to
disk. This can happen in a number of special cases, but what’s really important
is that Oracle guarantees that the redo log buffer will be flushed to disk after
a commit operation occurs. When you make changes in the database you must commit
them to make them permanent and visible to other users.
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