Commits on Jul 30, 2024

1. pubsub: fix a subtle race in catch up logic for barely active subs …

   The order of events processing when Corrosion is handling a change is:
     - determine changes
     - send changes to the channel
     - commit changes to sub DB
   
   When Corrosion client is catching up it subscribes to changes sent to
   the channel and queries the full sub DB. It's possibly that the query
   is run *before* the changes are committed, but after they've been sent
   to the channel, so what happens is:
   
     * A change with ID N is processed by Corrosion and sent to the channel
     * catch up logic starts and subscribes to changes, but doesn't see
       this change
     * sub DB is read and sent to the client, last committed change ID is
       N - 1, so EndOfQuery{change_id: N - 1} is sent to the client
     * corrosion commits the last update so the last change in the DB becomes
       N
     * catch up handler has min_change_id = N - 1 + 1, so when it compares
       last sent change ID (N) with min_change_id (N) it ignores it becase
       the comparison is strictly greater.
   
   min_change_id is what we expect to receive, so the fix is trivial -
   comparison should be greater or equal.

   

   pborzenkov committed Jul 30, 2024
   Configuration menu

   • View commit details
   • Copy full SHA for 82e6879
   • Browse repository at this point

   Copy the full SHA

   82e6879 View commit details

   Browse the repository at this point in the history