31 May
2017
31 May
'17
2:45 p.m.
On Wed, May 31, 2017 at 12:15 PM, Guillaume Delhumeau
<guillaume.delhumeau(a)xwiki.com> wrote:
Help me to decide!
TL;DR:
* I need to know if performing a query on the database for each user who
want to receive an email with all the notifications, is a scalability issue
(in a job context).
* If it's not an issue, I can implement the "naïve" solution which
requires
less development.
Full message:
Status:
* notifications are displayed on the top menu when you browse the wiki.
* notifications are displayed differently for each individual user
according to their preferences (filters on event type, on locations,
etc...).
* similar notifications are grouped together into "composite notifications".
* there is only a few notifications displayed (5 by default).
Objective:
* send an email periodically (every hour, every day, every week) according
to the user preferences with ALL events that happened during the last
period of time, but still according to the user preferences.
Inspiration:
* the watchlist gets ALL events that happened during the last period of time
* then, for each user, remove the events which the user is not interested in
* Benefit: only one query to get the events from the database for all users
Problems:
* in the notifications, I have introduced a NotificationFilter role the
make possible to inject some SQL in the query to get the events according
to the user preferences. I call this "pre-filters".
** it means we generate a unique request for each individual user, so if we
send a mail to 1000 users, we will have 1000 requests to the database.
I wonder if it's a non-problem or a big scability issue. Because even if
the whole job that send emails take ~10 minutes, it does not matter. It's
not a realtime thing.
Not sure what is the best yet but note that what the Watchlist is
currently doing is a big scalability issue as soon as you do a lot of
things between two watchlist schedules even when no user enabled
anything. See http://jira.xwiki.org/browse/XWIKI-10594. So I would
really not recommend keep doing the same behavior.
In other words whatever design you choose make sure it does not
involve putting in memory all the events you need to manipulate
because you have no idea how many you will end up with.
For the records, NotificationFilter have "post-filters" too, that perform
check on the event itself (for example checking the permissions, etc...).
Alternatives:
* just like the watchlist, perform a very generic query on the database to
get all the events that happened during the last period of time
* then for each user, use only the "post-filters" to remove events the user
don't care of
Problem:
* it means the pre-filters that make sense in the notification use-case
cannot be used for emails. Developers must be aware of this.
* it requires some refactoring of the code that group similar notifications.
Question:
Should I go with the "naive" solution, ie for each user get all
notifications and send a mail, or should I go with the "only 1 query to the
database for all users" version?
Thanks,
--
Guillaume Delhumeau (guillaume.delhumeau(a)xwiki.com)
Research & Development Engineer at XWiki SAS
Committer on the XWiki.org project
--
Thomas Mortagne