li4wang commented on code in PR #1961:
URL: https://github.com/apache/zookeeper/pull/1961#discussion_r1067613912
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zookeeper-server/src/main/java/org/apache/zookeeper/server/ZooKeeperServer.java:
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@@ -1151,6 +1213,9 @@ protected void setLocalSessionFlag(Request si) {
}
public void submitRequest(Request si) {
+ if (state == State.MAINTENANCE) {
+ throw new IllegalStateException("Zookeeper server is in
maintenance state");
+ }
Review Comment:
> If you throw an exception here, the request will fail on the client side.
I haven't tried it myself, have you valdiated that the client is able to
seemlessly retry the command without bothering the user?
I checked the scenario of sending client request while zk is in maintenance
state. Here is what I found.
1. Connection/session creation will be retried but read/write operation will
not.
2. The read/write request will fail even no exception is thrown here,
because the request fails before sending to ZookeeperServer. Here is what
happens:
a) `ServerCnxn` detects that ZK server is not running and close the
socket/channel.
b) `ClientSocketCnxn.doTransport()` then detects that socket/channel is
closed and throws IOException
c) 'SendThread' catches the Exception, adds `ConnectionLoss` error reply
header, clears up the outgoingQueue ann pendingQueue, and attempts to
re-connect to server
d) Zookeeper check the header and sends ConnectionLoss to user
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