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Set primary extent size?

Posted on 2007-11-17
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Last Modified: 2013-12-24
Hi Experts,

I'm working on an ooooold INFORMIX 5.10 database, and want to change the "primary" extent (if that's what it's called) to say 1.5 times the current size of the loaded data, to maximise performance and allow for 50% growth without going into "secondary" extents (or is it "next"? extents).  The current data is badly fragmented, and the extent sizes are too small, so I plan to export, delete, and import the database.

Questions:

1. What is the correct term for this "primary" extent?

2. Does trying to avoid using next extents sound like a good way to maximise performance?  (Yes, I know there are many other ways - I'm just talking about this one).

3. I know how to set the next extent sizes ("ALTER TABLE...MODIFY NEXT SIZE..."), but how can I go about making the "primary"? extent 50% larger than the current data requirement?

4. Could I achieve item 3 by increasing the row counts in the dbexport file (after the export) by 50%, and then import?

5. Do those row counts in the dbexport file have to match the numbers of rows in the table unload files, for the dbimport to work?

6. Can the primary extent span chunks?  (I understand that next extents can't).

Thanks.
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Question by:tel2
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Expert Comment

by:gheist
ID: 20369104
It is set when initializing server based on config file
General recommendation is 128MB
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Author Comment

by:tel2
ID: 20439024
Hi gheist,

Sorry for the delay in responding.

What variable are you referring to?
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gheist earned 125 total points
ID: 20450103
confuded with root dbspace.
it is specified when one does create table.
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Author Comment

by:tel2
ID: 20453442
Hi gheist,

What do you mean by "confuded" (is it "confused"?).

Are you saying I should do this:
  CREATE TABLE abc ... EXTENT SIZE ...
?

TRS
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Expert Comment

by:gheist
ID: 20456928
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Author Comment

by:tel2
ID: 20461947
Awesome!

I'll take that as a double "yes".

Thanks gheist!
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Expert Comment

by:gheist
ID: 20462410
Informix Unleashed is best book on subject - it deals with some internals covered by Informix courses, not everything, but reasonalbly well.
First extent is allocated when table is created, next are allocated later many times and new ones can be set different size by ALTER TABLE
First extent should be data size when you import data, next is expected growth between UPDATE STATISTICS
They should be rounded up to page size (as taken from onstat) - 2k or 4k (8k page systems like old SunOS are long gone)
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Author Comment

by:tel2
ID: 20462424
OK - thanks again, gheist.
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