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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Compressing Export Dumps / WinZip
It all depends which words you use -- sorry for the ambiguity...
As Cary replied earlier, EXP just queries sys.seg$ (i.e. DBA_SEGMENTS) to find the bytes and uses that for the newly-calculated INITIAL. This can be seen in a SQL Trace initiated on the EXP's server process...
Tim,
I may be wrong but I thought that compress=y just adds up the total space
allocation from SEG$ rather than calculating them from storage parameters. I
know this is a trivial point but I'd appreciate the info if it sets about
things differently.
regards,
Mike Hately
-----Original Message-----
Sent: 16 May 2002 17:14
To: Multiple recipients of list ORACLE-L
The "compress=y" option doesn't have any effect on how data is stored in the export dump file, only some of the metadata.
It directs the EXP program to recalculate the DDL for all of the tables and indexes (instead of just using the settings in the data dictionary) so that all space previously allocated for the object is now contained in a single extent. In other words, if a table being exported had a STORAGE clause like:
storage (initial 1M next 1M pctincrease 0)
and it currently had 500 extents allocated to it, then the EXP program would store the DDL for the table in the export dump file with a new STORAGE clause:
storage (initial 500M next 1M pctincrease 0)
There are several flaws with this mechanism:
Although COMPRESS=Y is the default, I strongly advise that you use COMPRESS=N to disable this functionality, in most cases. Just my $0.02...
Patrice - That would be correct. If you run export interactively, the prompt
that is provided is "compress extents (y/n)".
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
Sent: Thursday, May 16, 2002 10:08 AM
To: Multiple recipients of list ORACLE-L
I don't know whether this is a tangent, but I notice that on the windows platform, "compressed" exports can still get 85% compression when zipping them with WinZip.
Obviously Oracle "compressed=y" doesn't mean "compress the export file", it just means that it places all the segments contiguously in the export file.
Right?
Regards,
Patrice Boivin
Systems Analyst (Oracle Certified DBA)
Systems Admin & Operations | Admin. et Exploit. des systèmes Technology Services | Services technologiques Informatics Branch | Direction de l'informatique Maritimes Region, DFO | Région des Maritimes, MPO
E-Mail: boivinp_at_mar.dfo-mpo.gc.ca
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