RecSys 2019 — sold out at record pace

Alan Said
Alan Said
Aug 28, 2019 · 6 min read

If you are reading this, you are likely aware of the fact that the 13th ACM Conference on Recommender Systems (RecSys 2019) is sold out. It sold out prior to the early bird registration deadline. This is a short description of how that happened, and how unprepared we were for it happening.

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First, a bit of a background.


In late 2015, we started talking about maybe attempting to bring RecSys to Scandinavia. RecSys 2015 had just closed, it had been the largest RecSys conference to date with a whopping 480 attendees. Fast forward to 2016. RecSys 2016 has a record-breaking 560 attendees. During the conference, we get our bid for RecSys 2019 approved by the ACM RecSys Steering Committee.

After this, we slowly start our preparations for the 2019 conferece. While planning a conference like RecSys, you attempt to estimate the number of attendees, and, together with ACM, sketch a budget with a break-even result at a certain number of participants. For RecSys 2019, the break-even number was set to 650. From this point, you plan for a conference the size of the break-even number (plus or minus 10%). This number reflects on quite a lot of things in the planning, the venue being one. In the back of our heads, we knew that we might draw upwards 750 attendees, but this was highly unlikely given the growth of the conference till date.

In 2017, RecSys again grew. This time the conference drew 650 participants. Again record breaking, still within the expected margin.

When scouting for venues for RecSys 2019, we found this great place with a capacity of 800. Perfect! Venue booked. We’re now in January 2018.

Then comes RecSys 2018 in October with 820 attendees. That’s an increase of 170 participants compared to 2017 instead of the expected 50. The conference closed registration at 820, everyone who wanted a ticket got one.


After RecSys 2018, we started planning for a larger conference — 750+ participants. RecSys 2018 had been in North America, we figured that a conference in Europe would have a lower number of attendees (attendees from US/Canada account for~25–30% of the conference).

With the venue prepared for 750–800 people, planning of RecSys 2019 continued as expected. Call for papers, workshops, tutorials, etc. were published, contributions were submitted, notifications sent. Everything seemed to be on track.

What usually happens after the notifications for the various contributions have been sent, is that authors start registering. Then comes the early bird registration deadline, after sufficient time has been given for authors and contributors to register. Just prior to this deadline, there is often a surge in registrations coming in. Somewhere around this point starts the process of cross-checking all contributions to registrations, making sure there is at least one person registered per contribution, i.e. making sure that the person who will be presenting the contribution at the conference has registered.

After this, the pace of registrations drops a little to pick up again just before the conference.

This is the expected scenario.

2019 took a different route.


In late June, registrations for RecSys opens. During the first few weeks, the pace of registrations is somewhat lower than 2018. Great. Things are looking good.

A few weeks after opening, the pace of registrations picks up. Still remaining manageable.

In the one or two days before the early bird registrations, the pace increases again. Realizing that we’ll sell out, we close the registration system at 750. This was to make sure we had enough spots for presenters, sponsors, and others who in some way contribute to the making of the conference (workshop organizers, tutorial speakers, student volunteers, workshop keynote speakers, etc. etc.) who had not registered yet. As you may realize, this is a long list.

The graph below shows the pace of registrations for the 2019 conference (blue) and the 2018 conference (orange). The 2018 timeline has been shifted to align with 2019 (this year, the conference is in mid September, in 2018 it took place in early October).

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RecSys 2018 and 2019 registration pace. 2018 number adjusted to correspond with 2019 timeline (counted as weeks before the conference)

Since we had to close registration a few days before the early bird deadline, many presenters and other contributors were not able to register on time. More than the 50 spots we had saved.

What starts now is the process of making sure that everyone who needs to be at the conference actually gets to be at the conference. We start compiling a long list of all accepted papers at the conference, at the workshops, etc. Plus we start reaching out to our sponsors who have not been able to use their complimentary registrations, (simply to make sure their exhibitions booths will be manned during the conference).

To make it somewhat more complicated, not all workshops had sent their notifications at this point (or even worse, not all had had their deadlines — something we advised against).

Needless to say, this process took a lot of time. After collecting a list of all accepted contributions (a few hundred if you put everything together), we had to figure out who the presenting author of each of these was, and make sure they got a chance to register. Now, doing this during a time when many people are on summer holidays makes this a lengthy process.

After a few weeks of hard work from our registration team, we had made sure all presenters were registered. The total number of registrations was now at quite a bit above 800, although within a margin that would still allow everyone to attend sessions (with no empty seats left — so if you’re going to be attending, make sure to not put your bags/coats etc. on neighboring seats).


This is where we’re at now (last week of August, 3 weeks to conference). We’ve had many, many requests from people wanting to come to RecSys. Many of these from people who had already booked their flights and hotels. Even though we would like to be able to accommodate all requests we’ve received, we can’t. There simply isn’t any more room in our venue. We’ve explored all possible options, we’ve been able to increase the number of spots available for workshops and tutorials. But in terms of the main conference, we are sold out. If you have your flights and hotels booked already, do go ahead and enjoy Copenhagen for a week. But, please be aware that we won’t have on-site registration.

There’s going to be a lot of people at this conference. We expect that space will be tight. To make the main auditorium a bit less cramped, we will have an overflow room to which all presentations from the main auditorium will be streamed live. The overflow room will be able to ask questions during the Q&A part of presentations, just as in the main auditorium.

If you are one of 800+ lucky people that have gotten hold of a ticket for the conference. Congrats! We hope you’ll enjoy the program. If you weren’t able to get a ticket, we will be recording all talks and will be uploading them to the ACM RecSys YouTube channel. While we won’t be streaming the talks, you might want to keep an eye on the #recsys2019 twitter feed as it will likely be very active. Also, remember to keep an eye on the RecSys website for information on RecSys 2020 in Rio. Foreseeing as they are, the General Chairs of RecSys 2020 have gone with a venue that will be able to fit considerably more attendees than ours.

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