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From "Michael Han (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ZOOKEEPER-2627) Remove ZRWSERVERFOUND from C client and replace handle_error with something more semantically explicit for r/w server reconnect.
Date Sun, 06 Nov 2016 05:21:58 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-2627?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Michael Han updated ZOOKEEPER-2627:
    Attachment: ZOOKEEPER-2627.patch

> 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
>         Attachments: ZOOKEEPER-2627.patch, ZOOKEEPER-2627.patch
> 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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