Database Reference
In-Depth Information
USERS
This tablespace is used to store users' data permanently. Like
TEMP tablespace, every database should have this tablespace
otherwise users' data will be saved in SYSTEM tablespace and
this does not fall under Oracle best practices guidelines.
Redo Log Files
Just a slight revision, we said the database is comprised of five
different types of files and we have learnt the purpose of each.
Among those five different types of files one is Redo log file.
We have learnt earlier in this chapter that a database should have
two or more redo log groups.
Each redo log group should have at
least two or more redo log files called members.
Within one Redo log group, all redo log files are mirror copies of
each other and its recommend that they all should reside on
different physical hard drives or tape drives to increase the fault
tolerance factor. Having mirror copies of the original Redo Log
file within a group is called Multiplexing of Redo Log files. Its
DBA's job to select how many Redo Log files mirroring is
required and where to place each mirrored copy.
Whatever data changes are happening in the database, all gets
written to the Redo Log files. In other words you can say it's the
“Undo” copy of the original database. Keeping in focus Figure
3-8, Oracle Instance (or more precisely, the Log Writer process)
writes these changes in data in Redo Log group 1, once it gets
filled up, Oracle instance will move to group 2 and finally group
3. Once group 3 finishes up, Oracle instance will start all over
gain from group 1. That's the reason we say that Redo Log files
get utilized in a circular fashion.
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