dcausse created this task.
dcausse added a project: Wikidata-Query-Service.
Restricted Application added a subscriber: Aklapper.
Restricted Application added a project: Wikidata.
TASK DESCRIPTION
As a WDQS user I want to know if the results I see come from a server that is
potentially lagged so that I can evaluate if they are stale.
Current the WDQS UI reports a latency metric querying the backend for the
following triple:
select ?lastUpdated where { <http://www.wikidata.org> schema:dateModified
?lastUpdated }
This technique assumes couple things that might not be true:
- the server this metric is obtained from is the same that the one the results
- the latency is stable without out of order events
Solving the first assumption might possible by changing how the UI presents
this data to the user and instead of decoupling the display of this metric and
the display of the results it could fetch this data from a HTTP header set by
the WDQS backend.
The WDQS backend could be with an additional set of servlet filter to
maintain in memory this latency metric.
The updater would set a custom header with the latency information that the
filter would use to update its memory structure.
The wdqs backend would set a custom header with this latency information it
has in memory.
The UI would compare the latency information with the client's "current time"
giving a rough estimate of whether or not the results might be stale according
to user expectations.
This solution works for cached response as well.
Solving the second point is more difficult but using the average of the event
times found in the batch being currently persisted might help.
AC:
- The WDQS UI reports the latency it finds in the response
- The WDQS UI no longer reports latency information that is not related to
the server serving the results
- The latency information is no longer stored in the triple store
- The WDQS backend reports latency information from a custom HTTP header
`X-Last-Event-Time` (name TBD)
- The WDQS backend updates its latency information from a custom HTTP header
`X-Set-Last-Event-Time` on write requests
- The event time is an average of the batch being processed
TASK DETAIL
https://phabricator.wikimedia.org/T278246
EMAIL PREFERENCES
https://phabricator.wikimedia.org/settings/panel/emailpreferences/
To: dcausse
Cc: dcausse, Aklapper, Invadibot, MPhamWMF, maantietaja, CBogen, Akuckartz,
Nandana, Namenlos314, Lahi, Gq86, Lucas_Werkmeister_WMDE, GoranSMilovanovic,
QZanden, EBjune, merbst, LawExplorer, _jensen, rosalieper, Scott_WUaS, Jonas,
Xmlizer, jkroll, Wikidata-bugs, Jdouglas, aude, Tobias1984, Manybubbles, Mbch331
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