What is the different between incremental and cumulative export ?
ye...@rnd.celcom.com.my
cumulative backup ?
Thank you
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Before you buy.
Alex Hudghton
Incremental - saves all files changed since the last backup
Cumulative - saves all files changed since the last FULL backup
Alex
Pete Sharman
answer both:
1. The export utility allows you to perform three levels of export -
complete (everything), cumulative (all tables that have changed since
the last cumulative or complete export) and incremental (all tables
changed since the last export, regardless of what the level was).
Theoretically, what this meant was you could set up an export regime
where you could do complete exports once a month, cumulative exports
once a week, and incremental exports each night, thus allowing smaller
and faster exports.
The problem was (and still is by the way) that the way export determined
whether a table had changed was by looking at some exp views created by
catexp.sql. These views are populated with information when a table
changes, so you might find that EMP had changed but not DEPT. What is
counted as a change is ANY data change. So for example, you could have
a 50 million row table with one row changed. The exp views would be
populated to say the table had changed, and the next export would export
the ENTIRE table, not just the row that was changed.
The result is that incremental and cumulative exports were virtually
useless. I believe they are not being enhanced at all, and they may go
away in a later release, but I haven't seen that officially confirmed
(personal opinion, yadda yadda yadda).
2. There is since Oracle8 with the RMAN utility the ability to do
backups of the data files that allow you to say I only want the blocks
that have changed. From memory, you can have 10 levels of backup with
RMAN, so it's really what allows the functionality you're after without
the overhead.
HTH.
Pete
Jeremiah Wilton
>
> >Can anyone tell me what is the different between incremental and
> >cumulative backup ?
Alex Hudghton wrote:
>
> I'd guess at :
>
> Incremental - saves all files changed since the last backup
>
> Cumulative - saves all files changed since the last FULL backup
Files?
Instead of guessing at answers, how about looking at the documentation?
Note that exports are a very bad way to perform backup. Oracle
encourages the use of physical backups for purposes of recovery. See the
Oracle8 Backup and Recovery Guide. A system restored from an export
cannot be recovered to a point in time using redologs. Also, restoring
from an export takes more time and is more complex than restoring a
physical backup.
--
Jeremiah
From Oracle8 Utilities Guide Release 8.0
------------
Base Exports
If you use cumulative and incremental Exports, you should periodically
perform a complete Export to create a base backup. Following the
complete Export, perform frequent incremental Exports and occasional
cumulative Exports. After a given period of time, you should begin the
cycle again with another complete Export.
Incremental Exports
An incremental Export backs up only tables that have changed since the
last incremental, cumulative, or complete Export. An incremental Export
exports the table definition and all its data, not just the changed
rows. Typically, you perform incremental Exports more often than
cumulative or complete Exports.
Cumulative Exports
A cumulative Export backs up tables that have changed since the last
cumulative or complete Export. A cumulative Export compresses a number
of incremental Exports into a single cumulative export file. It is not
necessary to save incremental export files taken before a cumulative
export because the cumulative export file replaces them.
Complete Exports
A complete Export establishes a base for incremental and cumulative
Exports. It is equivalent to a full database Export, except that it also
updates the tables that track incremental and cumulative Exports.
Alex Hudghton
and I'm not the only one who could have read the documentation!
Alex