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Subject [GitHub] [zookeeper] hanm commented on issue #1047: [ZOOKEEPER-3500] Improving the ZAB UPTODATE semantic to only issue it to learner when there is limited lagging
Date Wed, 14 Aug 2019 05:39:57 GMT
hanm commented on issue #1047: [ZOOKEEPER-3500] Improving the ZAB UPTODATE semantic to only
issue it to learner when there is limited lagging
URL: https://github.com/apache/zookeeper/pull/1047#issuecomment-521108755
 
 
   >> there will be lots of txns need to be replayed between NEWLEADER and UPTODATE
packet.
   
   I think these are the transactions queued on learner while SNAP sync is happening? 
   
   >> And we start to serve client traffic just after we received UPTODATE packet, which
means client will see lots of stale data.
   
   Does the stale data cause any issues? I think this is an optimization issue instead of
a correctness issue, and a client will never end up in a case where it fails to see its last
write when connect to a sync in flight server, and zookeeper's sequential consistency is still
guaranteed. If so, wondering why seeing stale data would be an issue if the servers will finally
converge?
   
   >> changed the time when ZK is applying the txns between NEWLEADER and UPTODATE.
   
   I think with this change the clients will have to expect a little bit longer recovery time
in certain cases - was there any concerns / discussions around this increased recovery time
on client side and the implications?

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