10.XC10 - Extent size modification

10.XC10 - Extent size modification

Post by Fernando N » Fri, 20 Mar 2009 21:13:34



Thanks... for the feature and for the explanation.
This has also some other implications:

- in truncate table
- In the table definition. Good for doing migrations. You can change it in the
original system and obtain a clean dbschema. I believe Art's tools could take
care of that currently, but it's always nice to have the features in the engine
- in features to appear in the near future. Keep and open eye on it... If
you're in the EVP you know what I'm talking about.

Regards.

--
Fernando Nunes
Portugal

http://www.yqcomputer.com/
My email works... but I don't check it frequently...
 
 
 

10.XC10 - Extent size modification

Post by Zach » Fri, 20 Mar 2009 21:47:09

n Mar 19, 8:13m, Fernando Nunes < XXXX@XXXXX.COM > wrote:

Two features I asked for was trim/drop LAST extent and better control
of extent size doubling. This is useful when you need to save the data
in a partition that will never be written to again and you do not want
to waste the space there - for example, you keep monthly partitions
and your average daily use is around 1GB, so you define first extent
of 25GB and next size 1GB. But different months carry different
amounts of data, because of number of days and variability in data. So
the system will allocate more extents (and larger ones, as it doubles
the extent size), and the last extent will retain unused space, which
might grow to be 4GB. This space currently cannot be returned to the
system. Were these features also implemented in this release (or in
11.1 or 11.5)?

 
 
 

10.XC10 - Extent size modification

Post by Jack Parke » Fri, 20 Mar 2009 22:02:09


A feature request I made shows up in this release of IDS. Going through the
documentation yesterday, the reasons for the feature are mentioned in
passing but not really explained. I thought I'd take the opportunity to do
so here.

As you may (or may not) know (or care). A pet project of mine has been the
use of partitioning to age off old data. On a daily basis you create a new
partition/fragment for tomorrows data. When that data ages off, instead of
deleting it, you just drop the old partition/fragment. Works great and very
quickly.

The issue comes in sizing tomorrows extent. Based on recent history, we
know about how much data it should house, and to ensure that the dbspace
does not get overly fragmented, we allocate size in multiples of some figure
so that we don't waste space with overly large extents, nor require too many
extra extents for that data. The problem is that the size of new partition
is controlled by FIRST EXTENT, not NEXT EXTENT. Historically you could not
change the first extent size. Which means that we could only work with NEXT
EXTENT size. So if we wanted 20MB for tomorrow, the partition would have a
512K default starting size + 19.5MB next size. Even worse, if the data size
prediction shrank to 100K, we would still allocate 512K and then attempt to
set NEXT SIZE to -400K (which drops a shared memory dump and af file for
some strange reason).

As of XC10, you can now modify the first extent size with ALTER TABLE foo
MODIFY EXTENT SIZE nnn. Which means we now have control over the size of
tomorrows data fragment. It does not change the size of existing extents,
just new partitions/fragments.

cheers
j.

Sane ego te vocavi. Forsitan capedictum tuum desit.
 
 
 

10.XC10 - Extent size modification

Post by Fernando N » Fri, 20 Mar 2009 22:37:45

achi wrote:

The feature Jack wrote about was introduced in 10.00.FC10, 11.10.FC3 and 11.50.FC3.
As far as I know nothing was changed in the extent doubling.
Further features related to this may be delivered soon. Keep an open eye for
next releases.

Regards.

--
Fernando Nunes
Portugal

http://informix-technology.blogspot.com
My email works... but I don't check it frequently...
 
 
 

10.XC10 - Extent size modification

Post by Jack Parke » Sat, 21 Mar 2009 11:46:54

f you partition on a monthly basis (add one partition per month), then your
problem would appear to go away?

cheers
j.


-----Original Message-----
From: XXXX@XXXXX.COM
[mailto: XXXX@XXXXX.COM ]On Behalf Of Zachi
Sent: Thursday, March 19, 2009 7:47 AM
To: XXXX@XXXXX.COM
Subject: Re: 10.XC10 - Extent size modification


On Mar 19, 8:13m, Fernando Nunes < XXXX@XXXXX.COM > wrote:
the
do
the
new
of
very
figure
many
partition
not
NEXT
have a
size
to
foo
extents,
the
take
engine

Two features I asked for was trim/drop LAST extent and better control
of extent size doubling. This is useful when you need to save the data
in a partition that will never be written to again and you do not want
to waste the space there - for example, you keep monthly partitions
and your average daily use is around 1GB, so you define first extent
of 25GB and next size 1GB. But different months carry different
amounts of data, because of number of days and variability in data. So
the system will allocate more extents (and larger ones, as it doubles
the extent size), and the last extent will retain unused space, which
might grow to be 4GB. This space currently cannot be returned to the
system. Were these features also implemented in this release (or in
11.1 or 11.5)?
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