[versioned maps] Investigate: many more "Stable cache miss" events than anticipated
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	awight
	May 11 2022, 10:50 AM

Description

We added logging to record each time mapdata is requested for a stable (but non-latest) revision of a page, which was not found in the FlaggedRevs parser cache. This was expected to be a rare edge case, since mapdata is normally requested in a second round-trip from the client, only after the page is rendered, so the page should already be in the cache. Instead, we're seeing a huge number of these events on certain wikis since the versioned maps deployment yesterday.

https://logstash.wikimedia.org/app/dashboards#/view/AXWYB4nN2lgCwKx7QZ8C?_g=h@d01ba18&_a=h@dfcb080

Let's debug and try to understand how this happens.

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Status	Assigned	Task
Resolved	None	T306872 Versioned Maps follow-up cleanup
Resolved	WMDE-Fisch	T307348 Enable Kartographer <mapframe> tag on remaining FlaggedRevision page-stabilized wikis
Resolved	None	T308119 [versioned maps] Investigate: many more "Stable cache miss" events than anticipated

Event Timeline

awight created this task.May 11 2022, 10:50 AM

Restricted Application added a subscriber: Aklapper. · View Herald TranscriptMay 11 2022, 10:50 AM

thiemowmde added a project: WMDE-TechWish-Sprint-2022-05-11.May 11 2022, 12:13 PM

thiemowmde moved this task from Sprint Backlog to Doing on the WMDE-TechWish-Sprint-2022-05-11 board.

thiemowmde set the point value for this task to 3.May 11 2022, 12:18 PM

Patch will be deployed with next week's train, or we can backport on Monday.

WMDE-Fisch moved this task from Backlog to In sprint on the WMDE-GeoInfo-FocusArea board.May 12 2022, 10:10 AM

thiemowmde updated the task description. (Show Details)May 17 2022, 1:50 PM

Note: As of today there is a sharp drop, just as anticipated. Before 2022-05-19 it's approx. 10,000 events/hour. After it's approx. 200/hour. In other words, we have a 98% cache hit rate. The remaining ones are all from wmf.12 wikis, mostly from ukwiki, vecwiki, and arwiki. My theory is that these are somehow connected to edits/previews, not to views.

WMDE-Fisch moved this task from Watching / Epic / Stalled to Doing on the WMDE-TechWish-Sprint-2022-05-11 board.May 24 2022, 8:38 AM

WMDE-Fisch moved this task from Doing to Sprint Backlog on the WMDE-TechWish-Sprint-2022-05-11 board.May 24 2022, 8:43 AM

thiemowmde added a project: WMDE-TechWish-Sprint-2022-05-25.May 25 2022, 8:25 AM

WMDE-Fisch mentioned this in T309188: [versioned maps] Investigate: Look into the remaining "Stable cache miss" events.May 25 2022, 10:28 AM

WMDE-Fisch added a parent task: T307348: Enable Kartographer <mapframe> tag on remaining FlaggedRevision page-stabilized wikis.

WMDE-Fisch moved this task from Sprint Backlog to Done on the WMDE-TechWish-Sprint-2022-05-25 board.

WMDE-Fisch closed this task as Resolved.Jun 7 2022, 12:35 PM