[GitHub] rdhabalia commented on issue #742: Avoid huge backlog on topic reloading: due to large gap between markDelete-offset and read-position of cursor.

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rdhabalia commented on issue #742: Avoid huge backlog on topic reloading: due to large gap between markDelete-offset and read-position of cursor.
URL: https://github.com/apache/incubator-pulsar/issues/742#issuecomment-326704021
 
 
   > We should already have that mechanism in place, right?
   
   Umm.. we have mechanism to block consumer if number of unack-msg reached to threshold (consumer > 50K and subscription > 4M). 
   However, frequently we are seeing issue with client when client has unack-msg < 50K but due to ack-holes, difference between markDelete-position and readPosition gets big (eg: 10M). In this case, when broker restarts, client often sees huge backlog and they consume same 10M messages again. 
   We are seeing this behavior often so, we feel there should be a mechanism where broker can notify consumer so, broker restart won't build huge backlog.
   I think we can solve this issue by increasing unack-msg range in cursor-metadata but then it can increase metadata footprint as well.
   +@saandrews 
 
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