Subject: Re: [HACKERS] make async slave to wait for lsn to be replayed
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, tgl@sss.pgh.pa.us
Cc: a.akenteva@postgrespro.ru, a.korotkov@postgrespro.ru,
 i.kartyshov@postgrespro.ru, amit.kapila16@gmail.com,
 pgsql-hackers@lists.postgresql.org
References: <20200408.100945.375702947246835193.horikyota.ntt@gmail.com>
 <d3ff2e363af60b345f82396992595a03@postgrespro.ru>
 <13716.1586378146@sss.pgh.pa.us>
 <20200409.161107.580344062273684114.horikyota.ntt@gmail.com>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <880834ee-4b18-6d5d-9dae-6520c5eb2bef@oss.nttdata.com>
Date: Thu, 9 Apr 2020 16:35:22 +0900
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On 2020/04/09 16:11, Kyotaro Horiguchi wrote:
> At Wed, 08 Apr 2020 16:35:46 -0400, Tom Lane <tgl@sss.pgh.pa.us> wrote in
>> Anna Akenteva <a.akenteva@postgrespro.ru> writes:
>>> I'd like to hear others' opinions on the syntax as well.
>>
>> Pardon me for coming very late to the party, but it seems like there are
>> other questions that ought to be answered before we worry about any of
>> this.  Why is this getting grafted onto BEGIN/START TRANSACTION in the
>> first place?  It seems like it would be just as useful as a separate
>> command, if not more so.  You could always start a transaction just
>> after waiting.  Conversely, there might be reasons to want to wait
>> within an already-started transaction.
>>
>> If it could survive as a separate command, then I'd humbly suggest
>> that it requires no grammar work at all.  You could just invent one
>> or more functions that take suitable parameters.
> 
> The rationale for not being a fmgr function is stated in the following
> comments.

This issue happens because the function is executed after BEGIN? If yes,
what about executing the function (i.e., as separate transaction) before BEGIN?
If so, the snapshot taken in the function doesn't affect the subsequent
transaction whatever its isolation level is.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION