Change 313318 had a related patch set uploaded (by EBernhardson):
[WIP] Perform interwiki searches with a multi-search

https://gerrit.wikimedia.org/r/313318

For click through based on faster/slower results, i think we can run a simpler test that slows down results by a few hundred ms and look at differences in behaviour. I don't think we need to test if this specific change has that effect.

To see if this change ends up having any effect on latency we should be able to look at response percentiles in hive pre and post deployment.

Change 313318 merged by jenkins-bot:
Perform interwiki searches with a multi-search

https://gerrit.wikimedia.org/r/313318

@EBernhardson Is the existing cross-wiki search on the Italian Wikipedia part of MediaWiki core, CirrusSearch, or something else? I'd like to know if I need to talk to the community there about this change or if this is all behind the scenes and will just Make Things Better™ :)

The interwiki search results on itwiki come from CirrusSearch, and are rendered by core. Likely we will need to talk to them, because we will be changing the results they get. Specifically the current design drafts show a single result per interwiki search result with highlights, whereas what itwiki currently gets is a list of up to 5 matching titles per wiki with no highlights.

We had some intention of using itwiki as one of the first testing grounds for changes to the interface, iirc.

I wasn't looking at what exactly this ticket is ... For the changes made specifically for this ticket itwiki shouldn't notice any particular difference, except that the results should come back faster.

I'd argue that " you'll get faster results" is a very interesting piece of information to be given to a community.

In T146179#2763596, @Elitre wrote:

I'd argue that " you'll get faster results" is a very interesting piece of information to be given to a community.

Indeed! Do you have any suggestions for the best place to leave that feedback on the Italian Wikipedia? Would we need to get the message translated, or would English suffice?

Local language is always better. Once Chris has all the info he needs about what was done, and further plans/details if any, I can support him of course.

Just added a small note to https://it.wikipedia.org/wiki/Discussioni_aiuto:Ricerca#I_risultati_della_ricerca_appaiono_pi.C3.B9_velocemente , which is linked from the VP. HTH.

@Elitre Thank you!

to put some numbers on it here is the change observed. Note that because we are currently routing search requests to codfw the numbers are a little more exagerated, because every request had to make the 30ms round trip between virginia and dallas:

The human translation:

Pre-change 50% of requests ran in less then 0.8 seconds, 95% of requests ran in less than 1.3 seconds. After the change 50% of requests ran in less than 0.2 seconds, and 95% of requests ran in less than 0.5 seconds.

These can also be read in reverse:
Pre-change 50% of requests ran in more than 0.8 seconds. 5% of requests ran in more than 1.3seconds. After the change 50% of requests ran in more than 0.2 seconds, and 5% of the requests ran in more than 0.5 seconds.