Caching Termbox output on the Wikibase side
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Description

AC
Implement the proposal defined in the Termbox and ParserCache Integration ADR.

Background
User-specific html must not be added to the ParserOutput (cache). The "old" PlaceholderEmittingEntityTermsView Termbox prevents that by rendering placeholders in place of the user-specific markup. The new Termbox has to implement some way to ensure that no user-specific markup (e.g. toggle state, language preferences) is added, possibly by rendering the Termbox for logged-in users at a later point in the request life cycle, e.g. on OutputPageBeforeHTMLHookHandler::doOutputPageBeforeHTML.

This has to be solved before deployment.

Details

	Subject	Repo	Branch	Lines +/-
	OutputPageBeforeHTMLHookHandler: editablity as a service	mediawiki/extensions/Wikibase	master	+298 -86

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Related Objects
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Status	Assigned	Task
Resolved	Lydia_Pintscher	T214899 Deploying Wikidata Termbox
Open	None	T214901 Show mobile termbox on Wikidata item and property pages
Resolved	Tarrow	T214902 Show mobile termbox on Wikidata test wiki
Resolved	• Lea_WMDE	T214679 Caching Termbox output on the Wikibase side
Resolved	• Lea_WMDE	T214839 Document decisions regarding Termbox and ParserOutput
Resolved	Jakob_WMDE	T215788 Save termbox result in ParserOutput placeholder, replace in before output
Resolved	Jakob_WMDE	T215793 Show user-specific termbox result for users with non-default configuration
Resolved	Jakob_WMDE	T216080 Ensure edit pen visibility is conditional
Resolved	• Lea_WMDE	T216156 Ensure termbox output is not cached in case the SSR request failed

Event Timeline

Jakob_WMDE created this task.Jan 25 2019, 11:07 AM

Restricted Application added a subscriber: Aklapper. · View Herald TranscriptJan 25 2019, 11:07 AM

Jakob_WMDE mentioned this in T213736: wb: verify ParserOutput caching happens per language fallback chain permutation.Jan 25 2019, 11:32 AM

Jakob_WMDE renamed this task from Termbox Caching to Caching Termbox output on the Wikibase side.Jan 28 2019, 12:51 PM

• Lea_WMDE added a parent task: T214902: Show mobile termbox on Wikidata test wiki.Jan 29 2019, 12:04 PM

• Lea_WMDE moved this task from Backlog to MVP tickets: In preparation on the Wikidata-Termbox board.Jan 30 2019, 2:42 PM

Jakob_WMDE updated the task description. (Show Details)Feb 11 2019, 11:22 AM

• Lea_WMDE triaged this task as Medium priority.Feb 11 2019, 11:53 AM

• Lea_WMDE edited projects, added Wikidata-Termbox-Iteration-9; removed Wikidata-Termbox.

• Lea_WMDE set the point value for this task to 5.

• Pablo-WMDE mentioned this in T208381: mediawiki - node SSR HTTP request follow-up [2*2h].Feb 12 2019, 3:17 PM

• Pablo-WMDE added a subtask: T216080: Ensure edit pen visibility is conditional.Feb 13 2019, 9:45 PM

gerritbot mentioned this in T212136: Pass editability status to ssr.Feb 22 2019, 10:40 AM

• Lea_WMDE added a project: Wikidata-Termbox-Iteration-10.Feb 25 2019, 11:53 AM

When looking at the different scenarios of how TermboxView is invoked and what happens in error cases we observed an interesting behavior: TermboxView::renderTermbox() was invoked repeatedly (3 times) when running into SSR errors (i.e. no result written into ParserCache) while trying to display an item page.
Upon further investigation it was found that RefreshLinksJob & DerivedPageDataUpdater, i.e. jobs run after the connection to the client is already closed, are the source of the two extra calls.
Given that they do what they are designed to do and (actively or as a side effect) also ensure that ParserCache contains meaningful values this is expected behavior.

Risks:

in case of problems generating a termbox result (through a service request) the expiration time for this page's cache will be set to 0, i.e. every following request (incl. but not limited to jobs) will also try to generate a termbox result by the same means until a result is found and successfully persisted in the ParserCache

Possible mitigations:

implement some form of throttling (for that scenario in particular or any request in general)

Change 494717 had a related patch set uploaded (by Pablo Grass (WMDE); owner: Pablo Grass (WMDE)):
[mediawiki/extensions/Wikibase@master] OutputPageBeforeHTMLHookHandler: editablity as a service

https://gerrit.wikimedia.org/r/494717

gerritbot added a project: Patch-For-Review.Mar 6 2019, 1:44 PM

Change 494717 merged by jenkins-bot:
[mediawiki/extensions/Wikibase@master] OutputPageBeforeHTMLHookHandler: editablity as a service

https://gerrit.wikimedia.org/r/494717

• Lea_WMDE added a project: Wikidata-Termbox-Iteration-11.Mar 11 2019, 2:12 PM

Jakob_WMDE moved this task from To Do to Test (Product Review) on the Wikidata-Termbox-Iteration-11 board.Mar 12 2019, 1:40 PM

The languages shown on entity pages should now be identical for the new and the old termbox, ~~even~~ (edit: found an unrelated inconsistency: T218111) when server-side rendered. Steps to verify: