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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5098) Improving fault tolerance for connection between client and foreman node.
Date Sat, 10 Dec 2016 01:04:58 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15736881#comment-15736881
] 

ASF GitHub Bot commented on DRILL-5098:
---------------------------------------

Github user sudheeshkatkam commented on a diff in the pull request:

    https://github.com/apache/drill/pull/679#discussion_r91823124
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/client/DrillClient.java ---
    @@ -357,10 +357,54 @@ protected void afterExecute(final Runnable r, final Throwable t)
{
             super.afterExecute(r, t);
           }
         };
    -    client = new UserClient(clientName, config, supportComplexTypes, allocator, eventLoopGroup,
executor);
    -    logger.debug("Connecting to server {}:{}", endpoint.getAddress(), endpoint.getUserPort());
    -    connect(endpoint);
    -    connected = true;
    +
    +    // "tries" is max number of unique drillbit to try connecting until successfully
connected to one of them
    +    final String connectTriesConf = (props != null) ? props.getProperty("tries", "5")
: "5";
    +
    +    int connectTriesVal;
    +    try {
    +      connectTriesVal = Math.min(endpoints.size(), Integer.parseInt(connectTriesConf));
    +    } catch (NumberFormatException e) {
    +      throw new InvalidConnectionInfoException("Invalid tries value: " + connectTriesConf
+ " specified in " +
    +                                               "connection string");
    +    }
    +
    +    // If the value provided in the connection string is <=0 then override with 1
since we want to try connecting
    +    // at least once
    +    connectTriesVal = Math.max(1, connectTriesVal);
    +
    +    int triedEndpointIndex = 0;
    +    DrillbitEndpoint endpoint;
    +
    +    while (triedEndpointIndex < connectTriesVal) {
    +      client = new UserClient(clientName, config, supportComplexTypes, allocator, eventLoopGroup,
executor);
    +      endpoint = endpoints.get(triedEndpointIndex);
    +      logger.debug("Connecting to server {}:{}", endpoint.getAddress(), endpoint.getUserPort());
    +
    +      try {
    +        connect(endpoint);
    +        connected = true;
    +        logger.info("Successfully connected to server {}:{}", endpoint.getAddress(),
endpoint.getUserPort());
    +        break;
    +      } catch (InvalidConnectionInfoException ex) {
    +        logger.error("Connection to {}:{} failed with error {}. Not retrying anymore",
endpoint.getAddress(),
    +                     endpoint.getUserPort(), ex.getMessage());
    +        throw ex;
    +      } catch (RpcException ex) {
    +        ++triedEndpointIndex;
    +        logger.error("Attempt {}: Failed to connect to server {}:{}", triedEndpointIndex,
endpoint.getAddress(),
    +                     endpoint.getUserPort());
    +
    +        // Close the connection
    +        if (client.isActive()) {
    --- End diff --
    
    The loop recreates a new client anyway. So this should be closed, regardless of being
active.


> Improving fault tolerance for connection between client and foreman node.
> -------------------------------------------------------------------------
>
>                 Key: DRILL-5098
>                 URL: https://issues.apache.org/jira/browse/DRILL-5098
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Client - JDBC
>            Reporter: Sorabh Hamirwasia
>            Assignee: Sorabh Hamirwasia
>              Labels: doc-impacting, ready-to-commit
>             Fix For: 1.10
>
>
> With DRILL-5015 we allowed support for specifying multiple Drillbits in connection string
and randomly choosing one out of it. Over time some of the Drillbits specified in the connection
string may die and the client can fail to connect to Foreman node if random selection happens
to be of dead Drillbit.
> Even if ZooKeeper is used for selecting a random Drillbit from the registered one there
is a small window when client selects one Drillbit and then that Drillbit went down. The client
will fail to connect to this Drillbit and error out. 
> Instead if we try multiple Drillbits (configurable tries count through connection string)
then the probability of hitting this error window will reduce in both the cases improving
fault tolerance. During further investigation it was also found that if there is Authentication
failure then we throw that error as generic RpcException. We need to improve that as well
to capture this case explicitly since in case of Auth failure we don't want to try multiple
Drillbits.



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