@hoo @Lucie so I just took a quick look at the webrequest data and getting the numbers via that means will be fine and would provide us with daily data. An example entry can be seen below..

{"http_method":"GET","uri_host":"cy.wikipedia.org","uri_path":"/wiki/Arbennig:AboutTopic/Q432087","uri_query":"""referer":"https://cy.wikipedia.org/w/index.php?search=chris+ryan&title=Arbennig:Search&go=Go&searchToken=eo5w649tpumdso7dk6y9l06o5","x_analytics":"ns=-1;special=AboutTopic;loggedIn=1;WMF-Last-Access=15-Aug-2016;https=1"}

As we already do we can identify when the AboutTopic special page has been hit by using the 'special' element of the x_analytics header which would be 'AboutTopic' for the page in all languages (alongside a ns of -1)

Matching Special:Search from the referrer will be slightly harder, as we can not use the namespace to match the string as it is different in different languages (and there is no sort of normalisation done (we could of course come up with some crazy normalisation)
The parameters in the URL however will always be there, so we could match referers that include a search= param and maybe a searchToken? and also make sure that the referer hostname is the same as the uri hostname?

Thoughts?

Referrer has same host name and contains [?&]search and maybe a title with a colon sounds fine with me and would probably be robust against changes in Special:Search.

So something like this looks pretty solid.

SELECT * from wmf.webrequest
WHERE year = 2016
    AND month = 08
    AND day = 20
    AND webrequest_source = 'text'
    AND x_analytics_map["ns"] = '-1'
    AND x_analytics_map["special"] = 'AboutTopic'
    AND normalized_host.project_class = 'wikipedia'
    AND referer rlike '^.*search=.*$'
    AND referer rlike '^.*wikipedia\.org.*$'

Change 305989 had a related patch set uploaded (by Addshore):
WikidataArticlePlaceholderMetrics also send search referral data

https://gerrit.wikimedia.org/r/305989

Change 305989 merged by jenkins-bot:
WikidataArticlePlaceholderMetrics also send search referral data

https://gerrit.wikimedia.org/r/305989

This is now just pending a deployment

All deployed and dashboard updated.

https://grafana.wikimedia.org/dashboard/db/article-placeholder