Re: Minor point about contrib/xml2 functions "IMMUTABLE" marking - Mailing list pgsql-hackers

From Bruce Momjian
Subject Re: Minor point about contrib/xml2 functions "IMMUTABLE" marking
Date
Msg-id 200510131557.j9DFvun03738@candle.pha.pa.us
Whole thread Raw
In response to Re: Minor point about contrib/xml2 functions "IMMUTABLE" marking  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Neil Conway wrote:
> >> If a function's return value for a particular set of arguments could
> >> change within a single table scan, the function is volatile -- ISTM
> >> xslt_process() clearly falls within that definition.
> 
> > My thought was that a web page lookup is going to be a very expensive
> > operation, so you would not want it to requery inside a transaction.
> 
> > It is not like random() where you want it to be re-called and it is
> > inexpensive.
> 
> "It's too expensive" is not a valid rationale for claiming that
> something is stable when it is not.  In any case, you have fallen into
> the all too common trap of supposing that these labels have something
> to do with caching function results.  Calling it stable is not going
> to improve performance, only create a risk of wrong answers.

Well, should be marked as VOLATILE?  A web lookup?

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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