RE: Old Chestnut: Tablespace Fragmentation

From: <hemantchitale_at_charteredsemi.com>
Date: Mon, 04 Mar 2002 22:49:31 -0800
Message-ID: <F001.0041F28C.20020304224931@fatcity.com>

Darren,

To check if extents are contiguous query DBA_EXTENTS.

select file_id, block_id, blocks, block_id+blocks-1 from dba_Extents where segment_name = '&which_table'
and owner='&which_schema'
order by extent_id

Hemant K Chitale
Principal DBA
Chartered Semiconductor Manufacturing Ltd

"Browett, Darren" <dbrowett_at_city.coquitlam.bc.ca> 02/03/2002 12:48 AM Sent by: root_at_fatcity.com

Please respond to ORACLE-L

                                                                                                               
             To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>                                   
             cc: (bcc: CHITALE Hemant Krishnarao/IT/CHRT/ST Group)                                             
             Subject: RE: Old Chestnut:  Tablespace Fragmentation                                              
                                                                                                               
                                                                                                               
                                                                                                               

Is there anyway to check that the extents are contiguous ?

-----Original Message-----

[mailto:hemantchitale_at_charteredsemi.com] Sent: February 28, 2002 2:48 AM
To: Multiple recipients of list ORACLE-L

If you have only 1 Table in that Tablespace and only 1 File on that disk, even if you had multiple extents, you might expect them to be contiguous. Then, the only issue would be that the extent size should be a proper multiple
of db_block_size*db_file_multiblock_read_count (or max_io_size).

Hemant K Chitale
Principal DBA
Chartered Semiconductor Manufacturing Ltd

Bill Buchan <wbuchan_at_uk.intasys.com> 27/02/2002 08:43 PM Sent by: root_at_fatcity.com

Please respond to ORACLE-L

             To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>

             cc: (bcc: CHITALE Hemant Krishnarao/IT/CHRT/ST Group)

             Subject: Old Chestnut: Tablespace Fragmentation

I know this one has been done to death: use uniform extents to avoid fragmentation; multiple extents don't hurt (within limits).

But what if:

Data Warehouse, one big table on a single disk, full table (batch) scan, no

concurrent transactions on the database (so no contention for the disk), no

fragmentation at the file system level, initially empty buffer cache (startup), read-only operation so DBWR isn't doing anything on this disk. Basically I want to read one data file from end to end. Surely it would make sense to have the disk read moving smoothly from one end of the disk to the other rather than bouncing about all over the place as it may do with multiple extents "randomly" allocated.

Any thoughts?

Thanks
- Bill.

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Author: Bill Buchan
  INET: wbuchan_at_uk.intasys.com

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Author: Browett, Darren
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Author:
  INET: hemantchitale_at_charteredsemi.com

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