dcausse added a comment.

  In T248449#6411584 <https://phabricator.wikimedia.org/T248449#6411584>, 
@Zbyszko wrote:
  
  > In T248449#6411542 <https://phabricator.wikimedia.org/T248449#6411542>, 
@dcausse wrote:
  >
  >> In T248449#6382230 <https://phabricator.wikimedia.org/T248449#6382230>, 
@Zbyszko wrote:
  >>
  >>> We need to decide our approach on possible data corruption issues as 
well. One that comes to mind is a rev create with revid higher than previouis 
page delete.
  >>
  >> All scenario could happen if events are received out of order and are not 
necessarily "data corruption", revcreate with revid > a previous page delete 
may happen if a page-undelete event for this revid is late.
  >
  > Right, I wasn't aware back when writing a comment how exactly undeletes are 
handled - probably in most case that will be out of order events. I'm wondering 
how should we treat those situation - if we won't receive some intermediate 
revision, we simply diff the newer one received and ignore the one out of 
order. Should we treat page undeletes events the same way?
  
  I don't know... I hope that for the most cases late events will properly be 
detected by the window function and thus logged accordingly in a side output. 
For other situations, serious bug in MW, changeprop failing to propagate a 
particular topic, machines with completely unsynced clocks or any other serious 
issue affecting the validity of the streams we should aim imho to detect these 
as much as we can and log to the spurious-events side output anything that we 
think is suspicious. I would not try (yet) to recover such inconsistencies but 
rather learn what are the most common problems and tune the stream accordingly. 
Baring any lost events I think we should be able to track all these problems, 
either because lateness or because inconsistent with the current state.

TASK DETAIL
  https://phabricator.wikimedia.org/T248449

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To: dcausse
Cc: dcausse, Aklapper, Zbyszko, CBogen, Akuckartz, darthmon_wmde, 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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