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From: Matthias van de Meent <[email protected]>
To: Kyotaro Horiguchi <[email protected]>
Cc: [email protected]
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: TRAP: FailedAssertion("HaveRegisteredOrActiveSnapshot()", File: "toast_internals.c", Line: 670, PID: 19403)
Date: Tue, 29 Mar 2022 12:50:09 +0200
Message-ID: <CAEze2Wgv4FNYjjtY13HzgC+affAXsSVJYiztrN149B6+O+zq7Q@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>

On Tue, 29 Mar 2022 at 11:10, Kyotaro Horiguchi <[email protected]> wrote:
>
> At Tue, 29 Mar 2022 17:06:21 +0900 (JST), Kyotaro Horiguchi <[email protected]> wrote in
> > At Mon, 28 Mar 2022 18:36:46 +0900 (JST), Kyotaro Horiguchi <[email protected]> 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

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