Fangmin Lv created ZOOKEEPER-3356:
-------------------------------------

             Summary: Request throttling in Netty is not working as expected 
and could cause direct buffer OOM issue 
                 Key: ZOOKEEPER-3356
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3356
             Project: ZooKeeper
          Issue Type: Bug
          Components: server
    Affects Versions: 3.5.4, 3.6.0
            Reporter: Fangmin Lv
            Assignee: Fangmin Lv
             Fix For: 3.6.0


The current implementation of Netty enable/disable recv logic may cause the 
direct buffer OOM because we may enable read a large chunk of packets and 
disabled again after consuming a single ZK request. We have seen this problem 
on prod occasionally.
 
Need a more advanced flow control in Netty instead of using AUTO_READ. Have 
improved it internally by enable/disable recv based on the queuedBuffer size, 
will upstream this soon.
 
With this implementation, the max Netty queued buffer size (direct memory 
usage) will be 2 * recv_buffer size. It's not the per message size because in 
epoll ET mode it will try to read until the socket is empty, and because of 
SslHandler will trigger another read when it's not a full encrypt packet and 
haven't issued any decrypt message.



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