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Tablespace compress [message #197589] Wed, 11 October 2006 22:44 Go to next message
Messages: 261
Registered: January 2006
Senior Member

What is the need for setting COMPRESS option at the tablespace level & how it improves performance?

Re: Tablespace compress [message #197591 is a reply to message #197589] Wed, 11 October 2006 23:06 Go to previous messageGo to next message
Mohammad Taj
Messages: 2412
Registered: September 2006
Location: Dubai, UAE
Senior Member

Default: y

Specifies how Export and Import manage the initial extent for table data.

The default, COMPRESS=y, causes Export to flag table data for consolidation into one initial extent upon import. If extent sizes are large (for example, because of the PCTINCREASE parameter), the allocated space will be larger than the space required to hold the data.

If you specify COMPRESS=n, Export uses the current storage parameters, including the values of initial extent size and next extent size. The values of the parameters may be the values specified in the CREATE TABLE or ALTER TABLE statements or the values modified by the database system. For example, the NEXT extent size value may be modified if the table grows and if the PCTINCREASE parameter is nonzero.


Although the actual consolidation is performed upon import, you can specify the COMPRESS parameter only when you export, not when you import. The Export utility, not the Import utility, generates the data definitions, including the storage parameter definitions. Therefore, if you specify COMPRESS=y when you export, you can import the data in consolidated form only.


Neither LOB data nor subpartition data is compressed. Rather, values of initial extent size and next extent size at the time of export are used.
Re: Tablespace compress [message #197596 is a reply to message #197589] Wed, 11 October 2006 23:22 Go to previous message
Messages: 25581
Registered: January 2009
Location: SoCal
Senior Member
> how it improves performance?
The same way a ZIP file shortens file transfer time.
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