Smalyshev created this task.
Smalyshev assigned this task to Manybubbles.
Smalyshev added subscribers: Smalyshev, Manybubbles.
Smalyshev added projects: Search-Team, Wikidata-Query-Service.
Restricted Application added a subscriber: Aklapper.

TASK DESCRIPTION
  Currently with the multithreaded updater the following scenario can happen:
  
  # DB has revision 1 of Q42
  # Change comes for Q42 and is picked up by thread 1
  # Another change comes for Q42 and is picked up by thread 2
  # Thread 1 downloads Q42 data with revision 10
  # Thread 2 downloads Q42 data with revision 11
  # Thread 1 checks current revision, 1 < 10
  # Thread 1 checks current revision, 2 < 11
  # Thread 2 executes the update for revision 11 
  # Thread 1 executes the update for revision 10
  
  Since the order of execution of threads in not guaranteed, data is now from 
older revision (10) instead of new one (11). 
  
  In better case, if they are executed in order, one of the updates (for 10) is 
just a waste of time, but in worse case they can be in wrong order. We need to 
think about how to make it so that two different threads would not try to 
update same ID at the same time, or at least could not do it in a wrong order.

TASK DETAIL
  https://phabricator.wikimedia.org/T96121

REPLY HANDLER ACTIONS
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To: Manybubbles, Smalyshev
Cc: Manybubbles, Aklapper, Smalyshev, jkroll, Wikidata-bugs, Jdouglas, aude, 
GWicke, daniel, JanZerebecki



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