Subject: Re: Incorrect description of xmax and xip in functions docs
From: Simon Riggs <simon@2ndQuadrant.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: pgsql-docs <pgsql-docs@postgresql.org>
In-Reply-To: <200809071231.m87CVmD12043@momjian.us>
References: <200809071231.m87CVmD12043@momjian.us>
Content-Type: text/plain
Date: Mon, 08 Sep 2008 07:56:35 +0100
Message-Id: <1220856995.3913.62.camel@ebony.2ndQuadrant>
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On Sun, 2008-09-07 at 08:31 -0400, Bruce Momjian wrote:
> Simon Riggs wrote:
> > 
> > On Sat, 2008-09-06 at 21:31 -0400, Bruce Momjian wrote:
> > > Applied, and attached.
> > 
> > Thanks.
> > 
> > > > And for txid_visible_in_snapshot() comment added:
> > > > "Function should not be used with subtransaction xids. It is possible
> > > > that this function will return a true result for a subtransaction xid
> > > > that was actually still in progress at the time of the snapshot".
> > > 
> > > I think the cleaner solution is to throw an appropriate error if a
> > > subtransaction xid is used, rather than adding documentation.
> > 
> > Or maybe check subtrans for it, as it really should be doing.
> 
> Yea, that's what I meant.  You can't be sure everyone is going to read
> the documentation but they are sure to see the function results or error
> message.

In fact, neither is possible. We cannot assume subtrans is available on
the system on which the check is made, neither can we identify which
xids are subtransactions and which are not.

The only way is to document it.

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support