Re: Does max_standby_streaming_delay delay all WAL commits?

On Thu, Mar 3, 2016 at 8:15 PM, Venkata Balaji N <nag1010(at)gmail(dot)com> wrote:

>
> On Fri, Mar 4, 2016 at 2:43 AM, Dave Johansen <davejohansen(at)gmail(dot)com>
> wrote:
>
>> We're running into issues with canceled queries on a standby server and
>> have be debating between enabling hot_standby_feedback and setting
>> max_standby_streaming_delay to something large.
>>
>> Using max_standby_streaming_delay seems to have the advantage of keeping
>> the master independent of the standby, but will a long running query mean
>> that all WAL commits are delayed? Or just those that affected by the long
>> running query?
>>
>
> If you set max_standby_streaming_delay to a large value, WAL commits are
> going to continue until there is a conflict with the running queries on
> standby. If a WAL commit encounters a conflict, then the WAL update on
> standby will wait for "max_standby_streaming_delay" amount of time and
> until then all the subsequent WAL commits will be paused. In otherwords -
> entire standby recovery will be paused.
>

That's very helpful and based on that, I think we'll go with
hot_standby_feedback.

> Another alternative would be use "pg_xlog_replay_pause()" and
> "pg_xlog_replay_resume()" functions if that is possible with your
> application. Execute the "pg_xlog_replay_pause()" - then the query/job -
> then "pg_xlog_replay_resume()" function.
>

Unfortunately, that's not an option for our application.

Thanks,
Dave