Re: PL/pgSQL bug?

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, JanWieck(at)Yahoo(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: PL/pgSQL bug?
Date: 2001-09-07 16:16:10
Message-ID: 200109071616.f87GGBr07790@candle.pha.pa.us
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I am not sure if there is a TODO item here, but if there is, please let
me know. Thanks.

> > -----Original Message-----
> > From: Tom Lane
> >
> > I believe the reason for this is that in Read Committed mode,
> > each separate query from the client computes a new snapshot (see
> > SetQuerySnapshot calls in postgres.c). So, when your
> > "select ctid, i from t1" query executes, it computes a snapshot
> > that says T1 is committed, and then it doesn't see the row left
> > over from T1. On the other hand, your plpgsql function operates
> > inside a single client query and so it's using just one QuerySnaphot.
> >
> > One way to make the results equivalent is to compute a new QuerySnapshot
> > for each SPI query. Quite aside from the cost of doing so, I do not
> > think it makes sense, considering that the previous QuerySnapshot must
> > be restored when we return from the function. Do we really want
> > functions to see transaction status different from what's seen outside
> > the function call?
>
> Yes I do.
>
> > I doubt it.
> >
> > The other way to make the results the same is to omit the
> > SetQuerySnapshot calls for successive client-issued queries in one
> > transaction.
>
> What's different from SERIALIZABLE mode ?
>
> regards,
> Hiroshi Inoue
>
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