Re: StandbyRecoverPreparedTransactions recovers subtrans links incorrectly

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: StandbyRecoverPreparedTransactions recovers subtrans links incorrectly
Date: 2017-04-25 19:53:58
Message-ID: CANP8+j+1bQKWiBQyT7H4Hpoe_Cj0em7DN91sbgX1UapTdk2K2g@mail.gmail.com
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On 25 April 2017 at 16:28, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
>> I can't see any reason now why overwriteOK should exist at all. I'm
>> guessing that the whole "overwriteOK" idea was an incorrect response
>> to xids appearing where they shouldn't have done because of the
>> mistake you just corrected. So I will now remove the parameter from
>> the call.
>
> Seems reasonable, but I don't like the logic change you made in
> SubTransSetParent; you broke the former invariant, for non-Assert
> builds, that the target pg_subtrans entry is guaranteed to have
> the correct value on exit. I do like fixing it to not dirty the
> page unnecessarily, but I'd suggest that we write it like
>
> if (*ptr != parent)
> {
> Assert(*ptr == InvalidTransactionId);
> *ptr = parent;
> SubTransCtl->shared->page_dirty[slotno] = true;
> }

OK, thanks. I'll commit that tomorrow.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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