Thread: SI messages sent when excuting ROLLBACK PREPARED command

Hi

When reading the code FinishPreparedTransaction, I found that SI messages are sent 
when executing ROLLBACK PREPARED command.

But according to AtEOXact_Inval function, we send the SI messages only when committing the transaction .

So, I think we needn't send SI messags when rollbacking the two-phase transaction.
Or Does it has something special because of two-phase transaction?


Regards

"liuhuailing@fujitsu.com" <liuhuailing@fujitsu.com> writes:
> So, I think we needn't send SI messags when rollbacking the two-phase transaction.
> Or Does it has something special because of two-phase transaction?

Hmmm, yeah, I think you're right.  It probably doesn't make a big
difference in the real world --- anyone who's dependent on the
performance of 2PC rollbaxks is Doing It Wrong.  But we'd have
already done LocalExecuteInvalidationMessage when getting out of
the prepared transaction, so no other SI invals should be needed.

            regards, tom lane

Hi, tom

Thanks for your reply.

>Hmmm, yeah, I think you're right.  It probably doesn't make a big difference in the real world --- anyone who's
dependenton the performance of 2PC rollbaxks is Doing It Wrong. 
 
> But we'd have already done LocalExecuteInvalidationMessage when getting out of the prepared transaction, so no other
SIinvals should be needed.
 
Yes, it does not make any error.

But for the beginner,  when understanding the code,  it may make confused.
And for the developer, when developing based on this code, it may make unnecessary handling added. 

So, I think it is better to optimize the code.

Here is the patch.

Regards, liuhl

-----Original Message-----
From: Tom Lane <tgl@sss.pgh.pa.us> 
Sent: Thursday, July 15, 2021 1:36 AM
To: Liu, Huailing/刘 怀玲 <liuhuailing@fujitsu.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: SI messages sent when excuting ROLLBACK PREPARED command

"liuhuailing@fujitsu.com" <liuhuailing@fujitsu.com> writes:
> So, I think we needn't send SI messags when rollbacking the two-phase transaction.
> Or Does it has something special because of two-phase transaction?

Hmmm, yeah, I think you're right.  It probably doesn't make a big difference in the real world --- anyone who's
dependenton the performance of 2PC rollbaxks is Doing It Wrong.  But we'd have already done
LocalExecuteInvalidationMessagewhen getting out of the prepared transaction, so no other SI invals should be needed.
 

            regards, tom lane

 Hi, tom

> >Hmmm, yeah, I think you're right.  It probably doesn't make a big difference in
> the real world --- anyone who's dependent on the performance of 2PC rollbaxks
> is Doing It Wrong.
> > But we'd have already done LocalExecuteInvalidationMessage when getting
> out of the prepared transaction, so no other SI invals should be needed.
> Yes, it does not make any error.
> 
> But for the beginner,  when understanding the code,  it may make confused.
> And for the developer, when developing based on this code, it may make
> unnecessary handling added.
> 
> So, I think it is better to optimize the code.
> 
> Here is the patch.
There was a problem with the before patch when testing.  
So resubmit it.

Regards, Liu Huailing

On Tue, Aug 03, 2021 at 09:29:48AM +0000, liuhuailing@fujitsu.com wrote:
> There was a problem with the before patch when testing.
> So resubmit it.

FWIW, I see no problems with patch version 1 or 2, as long as you
apply patch version 1 with a command like patch -p2.  One thing of
patch 2 is that git diff --check complains because of a whitespace.

Anyway, I also think that you are right here and that there is no need
to run this code path with ROLLBACK PREPARED.  It is worth noting that
the point of Tom about local invalidation messages in PREPARE comes
from PostPrepare_Inval().

I would just tweak the comment block at the top of what's being
changed, as per the attached.  Please let me know if there are any
objections.
--
Michael

On Wed, Aug 11, 2021 at 03:14:11PM +0900, Michael Paquier wrote:
> I would just tweak the comment block at the top of what's being
> changed, as per the attached.  Please let me know if there are any
> objections.

And applied as of 710796f.
--
Michael

> On Wed, Aug 11, 2021 at 03:14:11PM +0900, Michael Paquier wrote:
> > I would just tweak the comment block at the top of what's being
> > changed, as per the attached.  Please let me know if there are any
> > objections.
> 
> And applied as of 710796f.
Thanks for your comment and commit.
I've changed the patch's commit fest status to 'committed'.
https://commitfest.postgresql.org/34/3257/

Regards,
Liu