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Date: Thu, 10 Sep 2020 17:22:27 +0300
From: Alexey Kondratov <a.kondratov@postgrespro.ru>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>,
 tsunakawa.takay@fujitsu.com, movead.li@highgo.ca, 'Amit Kapila'
 <amit.kapila16@gmail.com>, Masahiko Sawada
 <masahiko.sawada@2ndquadrant.com>, PostgreSQL-Dev
 <pgsql-hackers@postgresql.org>
Subject: Re: Global snapshots
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On 2020-09-09 20:29, Fujii Masao wrote:
> On 2020/09/09 2:00, Alexey Kondratov wrote:
>> 
>> According to the Sawada-san's v25 0002 the logic is pretty much the 
>> same there:
>> 
>> +2. Pre-Commit phase (1st phase of two-phase commit)
>> 
>> +3. Commit locally
>> +Once we've prepared all of them, commit the transaction locally.
>> 
>> +4. Post-Commit Phase (2nd phase of two-phase commit)
>> 
>> Brief look at the code confirms this scheme. IIUC, AtEOXact_FdwXact / 
>> FdwXactParticipantEndTransaction happens after 
>> ProcArrayEndTransaction() in the CommitTransaction(). Thus, I don't 
>> see many difference between these approach and CallXactCallbacks() 
>> usage regarding this point.
> 
> IIUC the commit logic in Sawada-san's patch looks like
> 
> 1. PreCommit_FdwXact()
>     PREPARE TRANSACTION command is issued
> 
> 2. RecordTransactionCommit()
>     2-1. WAL-log the commit record
>     2-2. Update CLOG
>     2-3. Wait for sync rep
>     2-4. FdwXactWaitForResolution()
>             Wait until COMMIT PREPARED commands are issued to the
> remote servers and completed.
> 
> 3. ProcArrayEndTransaction()
> 4. AtEOXact_FdwXact(true)
> 
> So ISTM that the timing of when COMMIT PREPARED is issued
> to the remote server is different between the patches.
> Am I missing something?
> 

No, you are right, sorry. At a first glance I thought that 
AtEOXact_FdwXact is responsible for COMMIT PREPARED as well, but it is 
only calling FdwXactParticipantEndTransaction in the abort case.


Regards
-- 
Alexey Kondratov

Postgres Professional https://www.postgrespro.com
Russian Postgres Company