Re: Throttling WAL inserts when the standby falls behind more than the configured replica_lag_in_bytes

On Thu, Dec 30, 2021 at 1:09 AM Andres Freund <andres(at)anarazel(dot)de> wrote:

> Hi,
>
> On 2021-12-29 11:34:53 -0800, SATYANARAYANA NARLAPURAM wrote:
> > On Wed, Dec 29, 2021 at 11:31 AM Andres Freund <andres(at)anarazel(dot)de>
> wrote:
> > Andres, thanks for the comments. Agreed on this based on the previous
> > discussions on this thread. Could you please share your thoughts on
> adding
> > it after SyncRepWaitForLSN()?
>
> I don't think that's good either - you're delaying transaction commit
> (i.e. xact becoming visible / locks being released).

Agree with that.

> That also has the danger
> of increasing lock contention (albeit more likely to be heavyweight locks /
> serializable state). It'd have to be after the transaction actually
> committed.
>

Yeah, I think that would make sense, even though we will be allowing a new
backend to get connected insert WAL, and get committed but after that, it
will be throttled. However, if the number of max connections will be very
high then even after we detected a lag there a significant amount WAL could
be generated, even if we keep long-running transactions aside. But I think
still it will serve the purpose of what Satya is trying to achieve.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com