unused space in extent and performance

unused space in extent and performance

Post by rob » Sat, 25 Apr 1998 04:00:00



I'am working on a data warahouse. The initial extents of tables and indexes
are sized to contain 5 years of data. For example: the largest table will be
about 2 GIG but now is filled with only 200MB of data.  Does a large ammount
of free space in the initial extents have a negitive effect on performance.

I have the feeling that choosing a more conservative initial extent will
benefit the performance in the first years. Ofcourse this will need
reorganising tables wen they are becomming to fragmented.

All comments are welcome
Rob.

 
 
 

unused space in extent and performance

Post by flang » Sat, 25 Apr 1998 04:00:00


Hi,
    Till your high water mark is set at 200Mega, there isn't any overcosts.
    The only trouble is disk waste.
        Backup and restore slower.
        Disk already bougth at the beginning of the project.
        ...

--
Regards F. Lange Certified DBA.
29A route du vin.
L5450 Stadtbredimus.
Grand Duchy of Luxembourg.

(int) 352 697412
(cel) 352 021193652
Phone numbers are variable length.
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Germany and Belgium.


>I'am working on a data warahouse. The initial extents of tables and indexes
>are sized to contain 5 years of data. For example: the largest table will
be
>about 2 GIG but now is filled with only 200MB of data.  Does a large
ammount
>of free space in the initial extents have a negitive effect on performance.

>I have the feeling that choosing a more conservative initial extent will
>benefit the performance in the first years. Ofcourse this will need
>reorganising tables wen they are becomming to fragmented.

>All comments are welcome
>Rob.


 
 
 

unused space in extent and performance

Post by Nevin and Cynthia Hah » Mon, 27 Apr 1998 04:00:00


Quote:>I'am working on a data warahouse. The initial extents of tables and indexes
>are sized to contain 5 years of data. For example: the largest table will
be
>about 2 GIG but now is filled with only 200MB of data.  Does a large
ammount
>of free space in the initial extents have a negitive effect on performance.

>I have the feeling that choosing a more conservative initial extent will
>benefit the performance in the first years. Ofcourse this will need
>reorganising tables wen they are becomming to fragmented.

>All comments are welcome

Rob,
Not to worry you'll be fine. You have prescribed to the notion that fitting
everything in one extent is the way to go. It does not hurt to have multiple
extents just so long as they don;t get out of contol. Having one extent
makes the object easy to manage, however it also prevents you from striping
the table across multiple disks. If you are using the Parallel Query Option
you may have I/O bottlenecking if the table resides on only one disk.

Cheers,
Nevin Hahn

 
 
 

1. unused extent space

Please see below an SQL by Lester Knutsen we use :-

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


--         Advanced DataTools Corporation
-- Discription: Displays free space in all dbspaces like Unix "df -k "
command
----------------------------------------------------------------------------
-
-- Note:On some versions (e.g 7.3)  need to use the 7.2 version of
--      this script to correctly display the truncated dbspace name.
--      If the dbspace name is blank - use the 72 version.

database sysmaster;

select    name[1,8] dbspace,       -- name truncated to fit on one line
          sum(chksize) Pages_size, -- sum of all chuncks size pages
          sum(chksize) - sum(nfree) Pages_used,
          sum(nfree) Pages_free,   -- sum of all chunks free pages
          round ((sum(nfree)) / (sum(chksize)) * 100, 2) percent_free
from      sysdbspaces d, syschunks c
where     d.dbsnum = c.dbsnum
group by 1
order by 1;

Regards

Glyn Balmer

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