azagrebin commented on pull request #12563:
URL: https://github.com/apache/flink/pull/12563#issuecomment-644170325


   When `EventTimeWindowCheckpointingITCase` runs the whole package, it 
sometimes hits the default JVM direct memory limit (2g). The GC of netty direct 
memory buffers is slowed down for some reason which leads to direct OOM errors 
in netty stack. This is also reproducible in `release-1.10` branch with a lower 
JVM direct memory limit (e.g. 512mb). This is not clear how inheritance in user 
class loaders, introduced in this PR, affects direct memory GC.
   
   We could reduce the usage of netty buffers by porting some network stack 
improvements to 1.10 from 1.11 (FLINK-15962) but we rather do not merge this 
change to 1.10 and reconsider it if this becomes a problem in future.
   cc @zhijiangW


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