Re: UPDATE STATISTICS
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I wanted to ask about updating statistics for stored procedures. Do you
need to
do that before they are created? Or after? We are installing store
procedures
for new tables, that will eventually have 150,000 rows in them.
We use HP 10.10 and Informix 5.03.
(Embedded
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Please respond to jparker@informix.com
To: informix-list @ rmy.emory.edu
cc: (bcc: Kate Tomchik/IS/SSC/THD)
Subject: Re: UPDATE STATISTICS
>
> Hi,
>
> I guess it does not write outputfile. It
> is a good idea to run after a bulk load of
> data,also you can incorporate it with your daily
> archiving script that is before archiving you can
> run an Update Statistics.
>
> Hope this helps !!
>
> Cheers
>
> Patrick Stacey wrote:
> >
> > 1. Can someone tell me if the UPDATE STATISTICS command generates an
> > output file for the DBA to read?
> >
> > 2. How often should you run this procedure?
> >
> > TIA,
> >
1 - In current versions of Online update statistics can generate
distribution
info on the data in each table (RTFM for more info). This is kept in
the sysmaster:sysdistributions table or some such. I believe it is
reportable using dbschema - but won't swear to it.
2 - How often? Depends on your application. If the table in question
is static then there is no need to continuallly update statistics for it.
If the table is dynamic then fresh statistics are vital for performance.
For example, if you create a table statistics indicate that the table is
empty - then you load it with 2000 rows - according to statistics the
table is still empty. Now try doing a read on the table - the optimizer
sees that the table is empty and hence it would be faster to read the
table sequentially than to do the extra read required to get an index.
Ouch. Granted that is a severe case.
At the same time doing an UPDATE STATISTICS HIGH can be expensive. UPDATE
STATISTICS itself is generally fairly cheap. With the current syntax you
can control exactly what level of update statistics you wish to do for each
table.
While you're at it don't forget to update stats for SPLs.
cheers
j.
________________________________________________________________________
jparker@informix.com Burlington, MA, USA (x1619)
"If anything can go wrong, fix it - to hell with Murphy."
________________________________________________________________________
Any opinions expressed herein are my own and not those of my employers.
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