| From: | "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de>, Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
| Subject: | Re: walsender performance regression due to logical decoding on standby changes |
| Date: | 2023-05-10 06:39:08 |
| Message-ID: | d211aa1b-eff8-6c76-18c8-6aa5ad5726b0@gmail.com |
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| Lists: | pgsql-hackers |
Hi,
On 5/9/23 11:00 PM, Andres Freund wrote:
> Hi,
>
> On 2023-05-09 13:38:24 -0700, Jeff Davis wrote:
>> On Tue, 2023-05-09 at 12:02 -0700, Andres Freund wrote:
>>> I don't think the approach of not having any sort of "registry" of
>>> whether
>>> anybody is waiting for the replay position to be updated is
>>> feasible. Iterating over all walsenders slots is just too expensive -
>>
>> Would it work to use a shared counter for the waiters (or, two
>> counters, one for physical and one for logical), and just early exit if
>> the count is zero?
>
> That doesn't really fix the problem - once you have a single walsender
> connected, performance is bad again.
>
Just to clarify, do you mean that if there is only one remaining active walsender that, say,
has been located at slot n, then we’d still have to loop from 0 to n in WalSndWakeup()?
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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