| From: | "Zeugswetter Andreas ADI SD" <ZeugswetterA(at)spardat(dot)at> |
|---|---|
| To: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Larry McGhaw" <lmcghaw(at)connx(dot)com> |
| Cc: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, "Dann Corbit" <DCorbit(at)connx(dot)com>, "Gregory Stark" <stark(at)enterprisedb(dot)com>, "Martijn van Oosterhout" <kleptog(at)svana(dot)org>, <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Selecting a constant question |
| Date: | 2007-06-12 09:37:56 |
| Message-ID: | E1539E0ED7043848906A8FF995BDA57902240F93@m0143.s-mxs.net |
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| Lists: | pgsql-hackers |
> > Again, *all* other major relational databases do this ...
> even blob fields have a maximum length reported from the database.
>
> So what are you doing with the max length? Not all data types
> and values have a meaningful max length, so you have to be
> able to deal with variable length data anyway.
Imho it has a lot to do with optimizing the interface.
If you know, that the max length is e.g. 16 bytes in UTF-8 for the 3
chars, you will probably not want any on the fly allocation smarts and
preallocate and bind those 16 bytes. When the max length value gets
larger, and it is a variable lenght type, the overhead of varlen
allocation smarts starts to pay off.
A generic interface should keep the sql parsing smarts at a minimum,
thus it cannot know that a returned column is actually a text constant.
Imho the request for a max length is very reasonable, but has no value
once it exceeds a certain size e.g. 64k.
Andreas
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