Right after I posted as user2, I reload the page for user1 then I instantly receive an alert.
I did it multiple times and it works that way always.
Alerts are sent instantly.
If you open up your browser debugger tools, you'll see a deferred.php call occur right after you post. This kicks off the notifications.
You can look at the tables; xf_thread_watch_pending and xf_forum_watch_pending to see estimated maximum possible recipients and people number of users actually sent to.
For example;
SQL:
select xf_thread_watch_pending.post_id, thread_id, sent, estimated_count, from_unixtime(start_time) as start_time, (end_time- start_time) as duration
from xf_thread_watch_pending
where from_unixtime(start_time) > '2017-08-01'
order by sent desc
limit 4;
select xf_thread_watch_pending.post_id, thread_id, sent, estimated_count, from_unixtime(start_time) as start_time, (end_time- start_time) as duration
from xf_thread_watch_pending
where from_unixtime(start_time) > '2017-08-01'
order by duration desc
limit 4;
In the last ~25 days;
# post_id, thread_id, sent, estimated_count, start_time, duration
'38156997', '512524', '4224', '4356', '2017-08-13 01:14:11', '35'
'38068269', '512524', '4206', '4310', '2017-08-10 16:11:30', '36'
'38377777', '517894', '4006', '4047', '2017-08-19 12:20:57', '80'
'38219838', '517894', '3999', '4044', '2017-08-14 20:44:55', '31'
# post_id, thread_id, sent, estimated_count, start_time, duration
'38215068', '395276', '6', '141', '2017-08-14 18:18:46', '94'
'38377777', '517894', '4006', '4047', '2017-08-19 12:20:57', '80'
'37994409', '420746', '24', '153', '2017-08-08 13:00:43', '68'
'38494306', '517894', '3767', '4057', '2017-08-22 22:13:17', '67'
And yes, that really is several threads with over 4000 watchers that take between 30 seconds to over a minute to notify
The important thing is the duration column; sure it is spread over multiple deferred.php requests, but you need roughly the same order of magnitude when someone posts a reply which triggers huge numbers of notifications.
No, it means they'll be processed in the background. It's more aimed for threads that have a significant number of watchers to be alerted.
And when you have
Persistent Alerts and
Thread Starter Alerts setup and have thousands of people being alerted at once.
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