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Re: xpath processing brain dead

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Eisentraut <peter_e(at)gmx(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Nikolay Samokhvalov <samokhvalov(at)gmail(dot)com>
Subject: Re: xpath processing brain dead
Date: 2009-02-26 20:54:08
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers

Robert Haas wrote:
> But the change you're proposing seems like
> it could CONCEIVABLY break a working application that counts on
> PostgreSQL's particular flavor of misbehavior, and therefore it seems
> questionable to put that into a stable branch.  The fact that the
> application perhaps should not have been written that way to begin
> with is neither here nor there.  We don't want people to be afraid of
> upgrading to the latest point release when we fix, say, a backend
> crash or a data corruption bug.

Let me reiterate the changes that I propose, and again challenge you to 
provide a working counter-example if you believe it will break anything 
not currently broken, even cases involving fragments.

First, I propose that we abandon this mangling, if, and only if, the xml 
is in fact a well formed XML document. Since the whole point of the 
mangling is to handle situations where the XML is not a well formed 
document, that seems fairly straight-forward. If this change were to 
upset any user, it must be because they are relying on undisputably 
incorrect results.

Second, I propose that, in the remaining cases, where we do mangle the 
XML, if the xpath expression does not begin with a '/', instead of 
prepending it with '/x/, which can not possibly be correct under any 
circumstance, we prepend it with '/x//' which has some possibility of 
giving correct results.

IOW, these proposals will expand the number of correct results from the 
code, without contributing any new incorrect cases. These changes are 
*very* conservative, as is usual when we fix things on stable branches.



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Subject: Re: xpath processing brain dead
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