Thanks Dave.
Dave Wotton wrote in message ...
>
>cc wrote in message ...
>>Oracle 7.3.4 on Unix
>>
>>I use "select sum(bytes) from user_segments where owner='JOHN'" and the
>>result is about 3GB.
>>
>>But use export owner=JOHN, the dump file only 800MB. Even full=y the dump
>>file is only about 1.2GB. Why is so different? Is there anyway can tell
>>roughly what the export dump file size will be?
>
>
>sum(bytes) is the total number of bytes used by blocks which have been
>allocated to the table. If your table initialisation parameters have been
>set up generously most of these blocks will be empty.
>
>An export file is effectively an SQL script to rebuild your database,
>containing CREATE TABLESPACE, CREATE TABLE, CREATE INDEX and INSERT INTO
>... VALUES (.....) statements. The number of INSERT INTO statements is
>obviously dependent on the number of actual rows in the table. However,
>there is a lot of textual overhead in an INSERT INTO statement compared
>to the row's compressed format in the database.
>
>It is therefore very difficult to correlate table size with export size.
>The only way to do it is "try it and see". One variation, if you are
>on Unix is to export to a named pipe and run a "wc" command at the
>other end of the pipe rather than create the export file.
>
>This was discussed in a thread here a few months ago. Try searching
>dejanews: (http://www.dejanews.com/home_ps.shtml)
>
>Specify: Subject = "Estimate the Size of an Full Database Export"
> Forum = "comp.databases.oracle.server"
> Date = 27/5/00 (dd/mm/yy)
>
>Dave.
>--
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>address first.
>
>
>
Received on Thu Jul 20 2000 - 00:00:00 CDT
