Re: Parallel scan with SubTransGetTopmostTransaction assert coredump

From: Andres Freund <andres(at)anarazel(dot)de>
To: Pengchengliu <pengchengliu(at)tju(dot)edu(dot)cn>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Parallel scan with SubTransGetTopmostTransaction assert coredump
Date: 2021-05-07 03:55:10
Message-ID: 20210507035510.he7e5hiu6dsi4rug@alap3.anarazel.de
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Hi,

On 2021-05-07 11:32:57 +0800, Pengchengliu wrote:
> Hi Hackers，
>
> Last email, format error, missing some information, so I resend this email.
>
> With PG 13.2(3fb4c75e857adee3da4386e947ba58a75f3e74b7), I tested subtransaction with parallel scan, I got a subtransaction coredump as below:

> So the root cause is the Parallel Workers process set the TransactionXmin with later transcation snapshot. When parallel scan, Parallel Workers process use the older active snapshot.
>
> It leads to subtrans assert coredump. I don't know how to fix it. Is there any ideas?

Do you have steps to reliably reproduce this?

Greetings,

Andres Freund

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