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From "Michael Han (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ZOOKEEPER-2627) Remove ZRWSERVERFOUND from C client and replace handle_error with something more semantically explicit for r/w server reconnect.
Date Thu, 03 Nov 2016 20:52:58 GMT
Michael Han created ZOOKEEPER-2627:
--------------------------------------

             Summary: Remove ZRWSERVERFOUND from C client and replace handle_error with something
more semantically explicit for r/w server reconnect.
                 Key: ZOOKEEPER-2627
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2627
             Project: ZooKeeper
          Issue Type: Bug
          Components: c client
    Affects Versions: 3.5.2
            Reporter: Michael Han
            Assignee: Michael Han
             Fix For: 3.5.3


While working on ZOOKEEPER-2014, I noticed a discrepancy between Java and C client regarding
the error codes definition. There is a {noformat}ZRWSERVERFOUND = -122{noformat} definition
in C client which is not present in Java client's KeeperException.Code definitions. 

This discrepancy was introduced by ZOOKEEPER-827, where the C client logic was simulating
the Java client's logic when doing a read/write server search while client is in read only
mode. Once client finds a valid read/write server, client will try to disconnect and reconnect
with this read/write server, as we always prefer r/w server in ro mode. The way Java client
is doing this disconnect/reconnect process is by throwing a RWServerFoundException (instead
of a KeeperException) to set the client in disconnected state, then wait for client reconnect
with r/w server address set before throwing the exception. C client did similar but instead
of having an explicitly disconnect / clean up routine, the client was relying on handle_error
to do the job where ZRWSERVERFOUND was introduced.

I propose we remove ZRWSERVERFOUND error code from C client and use an explicit routine instead
of handle_error when we do r/w server search in C client for two reasons:
* ZRWSERVERFOUND is not something ZK client users would need to know. It's a pure implementation
detail that's used to alter the connection state of the client, and ZK client users have no
desire nor need to handle such errors, as R/W server scanning and connect is handled transparently
by ZK client library.
* To maintain consistency between Java and C client regarding error codes definition. Without
removing this from C client, we would need to replace RWServerFoundException in Java client
with a new KeeperException, and again with the reason mentioned above, we don't need a KeeperException
for this because such implementation detail does not have to be exposed to end users (unless,
we provided alternative for users to opt-out automate R/W server switching when in read only
mode which we don't.).



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