From: Kartyshov Ivan <i.kartyshov@postgrespro.ru>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] make async slave to wait for lsn to be replayed
Date: Fri, 06 Mar 2020 15:21:49 +0300
Message-ID: <195e2d07ead315b1620f1a053313f490@postgrespro.ru> (raw)
On 2020-03-06 08:54, Kyotaro Horiguchi wrote:
> The syntax seems getting confused. What happens if we typed in the
> command "WAIT FOR TIMESTAMP '...' UNTIL TIMESTAMP '....'"? It seems
> to me the options is useles. Couldn't the TIMEOUT option be a part of
> event? I know gram.y doesn't accept that syntax but it is not
> apparent from the description above.
I`ll fix the doc file.
Synopsis
==========
WAIT FOR [ANY | SOME | ALL] event [, event ...]
and event is:
LSN value [options]
TIMESTAMP value
and options is:
TIMEOUT delay
UNTIL TIMESTAMP timestamp
> As I read through the previous thread, one of the reason for this
> feature implemented as a syntax is it was inteded to be combined into
> BEGIN statement. If there is not any use case for the feature midst
> of a transaction, why don't you turn it into a part of BEGIN command?
It`s seem to have some limitations on hot standbys. I`ll take few days
to make a prototype.
>> Description
>> ==========
>> WAIT FOR - make to wait statements (that are beneath) on sleep until
>> event happens (Don’t process new queries until an event happens).
> ...
>> Notice: WAIT FOR will release on PostmasterDeath or Interruption
>> events
>> if they come earlier then LSN or timeout.
>
> I think interrupts ought to result in ERROR.
>
> wait.c adds a fair amount of code and uses proc-array based
> approach. But Thomas suggested queue-based approach and I also think
> it is better. We already have a queue-based mechanism that behaves
> almost the same with this feature in the comit code on master-side. It
> avoids spurious backend wakeups. Couldn't we extend SyncRepWaitForLSN
> or share a part of the code/infrastructures so that this feature can
> share the code?
I`ll take a look on.
Thank you for your review.
Rebased patch is attached.
--
Ivan Kartyshov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
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To: pgsql-hackers@postgresql.org
Cc: i.kartyshov@postgrespro.ru, horikyota.ntt@gmail.com
Subject: Re: [HACKERS] make async slave to wait for lsn to be replayed
In-Reply-To: <195e2d07ead315b1620f1a053313f490@postgrespro.ru>
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