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Run a second synthetic A/A test
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Description

Background

The Experiment Platform team ran their first synthetic A/A test on all visitors in T392313: [Epic] SDS 2.4.11 Run a Synthetic A/A Experiment and its subtasks. Unfortunately, we discovered a bug that lead to the loss of nearly half of the analytics events were sent. We are confident that the distribution of the subject IDs in the events that we did receive is representative of the distribution of all subject IDs, we don't know how many distinct subjects participated in the test.

We would like to run a second synthetic A/A test for 1 week for a sample of 1% of traffic to enwiki to establish this number.

To do this we will duplicate and tweak the experiment configuration for T395342: Configure synthetic A/A experiment in xLab:

DetailConfiguration
Traffic allocationEnglish Wikipedia, 0.1%
Identifier typeedge-unique
Duration7 days
Experiment name (machine-readable name)SDS 2.4.11 Synthetic A/A Test 2 (sds2-4-11-synth-aa-test-2)
Treatment group name (machine-readable name)"Control 2" (control-2) "No changes for subjects in this group."
InstrumentationPageVisit, producing action: "page-visited" events client-side
Metrics"Page visits", "Page visits per hour"
NOTE: The PageVisit experiment/instrument will have to be updated.

AC

Event Timeline

phuedx renamed this task from Run another synthetic A/A test on logged-out users to Run a second synthetic A/A test on logged-out users.Jun 17 2025, 9:03 AM
phuedx updated the task description. (Show Details)
phuedx renamed this task from Run a second synthetic A/A test on logged-out users to Run a second synthetic A/A test.Jun 17 2025, 9:20 AM
phuedx updated the task description. (Show Details)

Change #1160169 had a related patch set uploaded (by Phuedx; author: Phuedx):

[mediawiki/extensions/WikimediaEvents@master] ext.wikimediaEvents: Repurpose PageVisit instrument

https://gerrit.wikimedia.org/r/1160169

Change #1160169 merged by jenkins-bot:

[mediawiki/extensions/WikimediaEvents@master] ext.wikimediaEvents: Repurpose PageVisit instrument

https://gerrit.wikimedia.org/r/1160169

Change #1160475 had a related patch set uploaded (by Phuedx; author: Phuedx):

[mediawiki/extensions/WikimediaEvents@wmf/1.45.0-wmf.6] ext.wikimediaEvents: Repurpose PageVisit instrument

https://gerrit.wikimedia.org/r/1160475

Change #1160475 merged by jenkins-bot:

[mediawiki/extensions/WikimediaEvents@wmf/1.45.0-wmf.6] ext.wikimediaEvents: Repurpose PageVisit instrument

https://gerrit.wikimedia.org/r/1160475

Mentioned in SAL (#wikimedia-operations) [2025-06-18T07:48:12Z] <phuedx@deploy1003> Started scap sync-world: Backport for [[gerrit:1160475|ext.wikimediaEvents: Repurpose PageVisit instrument (T397138)]]

Mentioned in SAL (#wikimedia-operations) [2025-06-18T07:50:40Z] <phuedx@deploy1003> phuedx: Backport for [[gerrit:1160475|ext.wikimediaEvents: Repurpose PageVisit instrument (T397138)]] synced to the testservers (see https://wikitech.wikimedia.org/wiki/Mwdebug). Changes can now be verified there.

Mentioned in SAL (#wikimedia-operations) [2025-06-18T08:05:07Z] <phuedx@deploy1003> Finished scap sync-world: Backport for [[gerrit:1160475|ext.wikimediaEvents: Repurpose PageVisit instrument (T397138)]] (duration: 16m 55s)

Created in xLab: https://mpic.wikimedia.org/read/sds2-4-11-synth-aa-test-2

If we're happy with the deetz, then I'll activate it.

Edit

The updated PageVisit instrument will be fully deployed by EOD Thursday (UTC+1). I've scheduled the experiment to start on Friday. I'm comfortable with this start date because we're reusing code that we've proven to work without error.

I think we're happy with the deetz!

mpopov triaged this task as Medium priority.Jun 18 2025, 7:47 PM

The experiment ran from 2025-06-20T12:00:00Z to 2025-06-27T00:00:00Z (confirmed in https://grafana.wikimedia.org/d/503b903b-ceff-4931-b435-e011cfcda0e8/edge-uniques?orgId=1&from=2025-06-20T11:00:00.000Z&to=2025-06-27T01:00:00.000Z&timezone=utc&var-site=esams&var-cluster=text&viewPanel=panel-1). The mismatched start and end times are explained with fixes for start time being partially rolled out and rolled back while the experiment was running.

The results of the experiment are here: https://superset.wikimedia.org/superset/dashboard/experiment-analytics/?native_filters_key=NTxGqWc_BGcObSgpQhmv81KPJ42o6MdGyaLWxeixaBEkJ33o66ov9oOrdoJ6TFhN

We are confident that the distribution of the subject IDs in the events that we did receive is representative of the distribution of all subject IDs, we don't know how many distinct subjects participated in the test.

We would like to run a second synthetic A/A test for 1 week for a sample of 1% of traffic to enwiki to establish this number.

As predicted, the distribution of the subject IDs in the received events is the same as before. We now know that 0.1% of all traffic to en.wikipedia.org and en.m.wikipedia.org corresponds to:

  • 139012 + 138916 = 277928 distinct logged-out subjects
  • 208 + 219 = 427 distinct logged-in subjects
Milimetric set the point value for this task to 1.