| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, a(dot)wicht(at)gmail(dot)com, pgsql-bugs(at)lists(dot)postgresql(dot)org, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> |
| Subject: | Re: BUG #15990: PROCEDURE throws "SQL Error [XX000]: ERROR: no known snapshots" with PostGIS geometries |
| Date: | 2021-05-12 16:13:54 |
| Message-ID: | 20210512161354.6msdekb4chsmpceh@alap3.anarazel.de |
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| Lists: | pgsql-bugs |
Hi,
On 2021-05-12 12:00:10 -0400, Tom Lane wrote:
> Yeah, on further thought, the real question to be asking here is
> "what's protecting that in-flight datum from becoming a dangling
> pointer?". AFAICT, the answer right now is "nothing". Therefore,
> it is *never* okay for plpgsql to be executing without a registered
> transaction snapshot; and it seems quite unlikely that it'd be any
> safer for any other PL.
A bit independently of this concrete issue, I wonder if we could make it
easier to detect such bugs. If we somehow™ associated an xmin horizon
with toasted datums, we could then assert before dereferencing that we
still guarantee that such a reference is still valid. The "somehow" part
obviously isn't entirely trivial, but it seems we could hack it by
encoding it as a different vartag?
Greetings,
Andres Freund
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