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From: llojd@earth.rivm.nl (Jan Diesel)
Newsgroups: comp.databases
Subject: Re: Informix SQL select time optimization
Keywords: Informix SQL
Message-ID: <1991Apr22.121930.5277@rivm.nl>
Date: 22 Apr 91 12:19:30 GMT
References: <1356@appli.se>
Sender: news@rivm.nl
Organization: Rijksinstituut voor Volksgezondheid en Milieuhygiene,Bilthoven,NL
Lines: 31

In article <1356@appli.se> niklas@appli.se (Niklas Hallqvist) writes:
>
>	Hello!
>
>I'm using Informix ESQL and have problems understanding how this
>product does it's queries.  Very often when I've typed down a complex
>select statement I find that it gets real slooooow, in spite of the
>possibility of getting a fast keyed search.  It seems that ISQL's
>heuristics fails to find the best search path throw the joins.  Is
>there some way to find out these heuristics?  If I knew them, I could
>always rearrange my select statements to reflect the search strategy
>ISQL imposes on them.  The only thing I've discovered myself so far
>is that the order of the tables specified in the from clause is very
>important if there are several ways to go about the search.
> [ examples deleted ]

Since it is virtually impossible to retrieve information concerning
the Informix optimizer I have the nasty feeling there may not be
anything like it in our Informix (version 2.1) product. Salespeople
assured me version 4 *does* have such a feature.
Nevertheless I found some hints regarding Informix performance in
the Informix 'Tech Notes' publication of Spring 1989, and some useful
information regarding Query Optimization in 'Tech Notes' of Spring 1987.

Good luck,
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Jan Diesel            llojd@rivm.nl
National Institute for Public Health and Environmental Protection
Laboratory for Air Research
P.O.Box 1, 3720 BA  BILTHOVEN, The Netherlands.
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