Option compress test in Oracle exp

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 import. If extent sizes are large (for example, because of the pctincrease parameter), the allocated space would be larger than the Space required to hold the data.

If you are specify Compress=n, Export uses the current storage parameters, including the values of initial extent size and NEX t extent size. The values of the parameters may are the values specified in the CREATE table or ALTER table statements or the values Modif IED by the database system. For example, the NEXT extent size value may modified if the table grows and if the pctincrease parameter is nonzero.

Note:

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

Note:

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.

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Compress=n very good understanding, table export extent is what kind of when the import or the original look; compress=y looks like Oracle is mainly to deal with pctincrease caused by the growing problem of extent , the following test the LMT under the autoallocate situation is understandable.

When the Oracle Import table is compress=y based on the segment size when the test is tested, extent does not adjust when the extent,compress=n is reassigned.

C:>sqlplus Test/test

Sql*plus:release 11.2.0.1.0 Production on Sunday September 16 21:09:37 2012

Copyright (c) 1982, Oracle. All rights reserved.

Connect to:

Oracle Database 11g Enterprise Edition release 11.2.0.1.0-production

With the partitioning option

Sql> CREATE TABLE TT tablespace users as SELECT * from Dba_objects;

Table has been created.

Sql> INSERT INTO the TT select * from TT;

16963 lines have been created.

Sql> commit;

Submit completed.

This article URL address: http://www.bianceng.cn/database/Oracle/201410/45563.htm

Sql> Select Extent_id,blocks from dba_extents where owner= ' TEST ' and segment_name= ' TT ';

extent_id BLOCKS

---------- ----------

0 8

1 8

2 8

3 8

4 8

5 8

6 8

7 8

8 8

9 8

10 8

extent_id BLOCKS

---------- ----------

11 8

12 8

13 8

14 8

15 8

16 128

17 128

18 128

19 rows have been selected.

--==============================

C:>exp test/test file=c:temptt_compress_y.dmp Tables=tt compress=y

Export:release 11.2.0.1.0-production on Sunday September 16 21:11:35 2012

Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.

Connect to: Oracle Database 11g Enterprise Edition release 11.2.0.1.0-production

With the partitioning option

Exported ZHS16GBK character set and Al16utf16 NCHAR character set

About to export the specified table through the general path ...

. . Exporting table TT exported 33926 rows

The export was successfully terminated and no warning occurred.

C:>exp test/test file=c:temptt_compress_n.dmp Tables=tt compress=n

Export:release 11.2.0.1.0-production on Sunday September 16 21:11:50 2012

Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.