Re: TRAP: FailedAssertion("HaveRegisteredOrActiveSnapshot()", File: "toast_internals.c", Line: 670, PID: 19403)

On Tue, 29 Mar 2022 at 11:10, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Tue, 29 Mar 2022 17:06:21 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> > At Mon, 28 Mar 2022 18:36:46 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> > Then, I found that portal->holdSnapshot is that. I came up with the
> > attached. It does the follows:
> >
> > 1. Teach PlannedStmtRequiresSnapshot() to return true for FetchStmt.
> >
> > 2. Use holdSnapshot in RunFromStore if any.
> >
> >
> > The rerpducer is reduced to as small as the following.
> >
> > CREATE TABLE t (a text);
> > INSERT INTO t VALUES('some random text');
> > BEGIN;
> > DECLARE c CURSOR FOR SELECT * FROM t;
> > FETCH ALL IN c;
> >
> > But I haven't come up with a reasonable way to generate the 'some
> > random text' yet.
>
> I gave up and took a straightforward way to generate one.
>
> I don't like that it uses a fixed length for the random text, but
> anyway it works for now...

An shorter (?) reproducer might be the following, which forces any
value for 'a' to be toasted and thus triggering the check in
init_toast_snapshot regardless of value length:

CREATE TABLE t (a text);
ALTER TABLE t ALTER COLUMN a SET STORAGE EXTERNAL;
INSERT INTO t VALUES ('toast');
BEGIN;
DECLARE c CURSOR FOR SELECT * FROM t;
FETCH ALL IN c;

Enjoy,

-Matthias