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Re: proof concept - access to session variables on client side

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: David Fetter <david(at)fetter(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: proof concept - access to session variables on client side
Date: 2012-06-26 21:17:12
Message-ID: 13361.1340745432@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> it is not security issue - just I dislike sending complete stack, when
> just only one variable should be used.

That's a pretty darn weak argument.  If I read the patch correctly, what
you're proposing involves a dynamic fetch from the client at runtime,
which is going to be disastrous for performance.  Quite aside from the
network round trip involved, the fetch function would have to be marked
volatile (since it has client-visible side-effects, not to mention that
we don't know when the client might change the variable value); which
would really hurt any query involving it, and probably lead to yet more
round trips.

Pushing over the known values once at session start (and individual
values after updates) is likely to be vastly better-performant than
this.  Matters could be improved further by requiring variables to be
sent to the server to be explicitly marked, which seems like a good
idea anyway in case anybody has security concerns that they're not
going to let you airily dismiss.

Another thing I don't care for is the unannounced protocol extension.
This feature is just not interesting enough to justify breaking
client compatibility, but that's what it would do as proposed.
Clients that haven't heard of this 'v' message would probably
think they'd lost sync and drop the connection.

(BTW, the patch doesn't seem to include the added backend source file?)

			regards, tom lane

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