I was just about to post a message asking the same thing. Many of us have seen
databases produce dumps which at first were much smaller than 2 GB, then we had to
pipe them through the native compress utility on UNIX to keep them that way, then we
used gzip which does a better job of compression, finally when this wasn't enough we
combined gzip with split. For the above, assume the backup system cannot handle files
over 2GB.
But why export routinely in the first place. They are not a good recovery mechanism.
Using an export almost always means loss of data. If a table is lost we can recover,
that tablespace, the system tablespace, and the rollback tablespace, to a
point-in-time just before the table was lost from our hot backups, and then export the
"lost" table fom this "mini" database and import it into
the one from which it was dropped. If an overzealous user ran some incorrect DML, we
can run the undo statement from log miner.
One can argue that if for some reason the physical backups are damaged, restoring
from an export with some loss of data is better than no recovery at all. It also
protects against errors in the physical backup script which may result in incomplete
backups. Export can aid in identifying bad table blocks as it selects every row from
every non "sys" table.
However, as your database grows larger selecting every row becomes more and more
expensive. Even if your exports are "inconsistent" they have an impact on rollback
segments. No, they do not produce any undo, however they do expect that the schemas
being exported stay the same. Schema changes while an export is underway can produce
snapshot too old errors and stop the export. Although now schema changes usally,
always? result in a failure to export just the table involved.
The problem with setting "optimal" for rollback segments is very likely to be exposed
by an export.
I am curious about the number of people who have stopped using them as part of their
daily backup strategy, and if you have. what are you doing to check for block
corruption. Assume the database is 24 X 7.
Ian MacGregor
Stanford Linear Acclerator Center
[EMAIL PROTECTED]
-----Original Message-----
Sent: Thursday, May 16, 2002 10:28 AM
To: Multiple recipients of list ORACLE-L
Simon,
I'm curious as to why you're creating exports that large.
Are you doing this as a backup method?
Have you ever restored an export that large?
The largest export I've ever restored is about 10 gig, and
it took far too long.
Jared
"Simon Waibale" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
05/16/2002 02:38 AM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
cc:
Subject: Compressing Export Dumps
Hi all,
My export dumps are too big (80 GB) for my filesystem and I'm looking for
a
way
to compress them on the fly -ie without taking *.dmp to disk first but
straight *.dmp.gz
Anybody with an idea on how to archive this ?
Thanking you,
---
CSW
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