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Date: Wed, 1 Aug 2012 18:52:03 +0000 (UTC)
From: "Eric Dong (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Created] (CASSANDRA-4479) Multiple phi_convict_threshold
 fields not all settable via JMX
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Eric Dong created CASSANDRA-4479:
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             Summary: Multiple phi_convict_threshold fields not all settable via JMX
                 Key: CASSANDRA-4479
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4479
             Project: Cassandra
          Issue Type: Bug
    Affects Versions: 1.1.2
            Reporter: Eric Dong


If a setting is configurable both via cassandra.yaml and JMX, the two should be consistent, but that is not the case for phi_convict_threshold.

I'm trying to set phi_convict_threshold via JMX, which sets FailureDetector.phiConvictThreshold_, but this doesn't update Config.phi_convict_threshold, which gets its value from cassandra.yaml when starting up.

Some places, such as FailureDetector.interpret(InetAddress), use FailureDetector.phiConvictThreshold_; others, such as AntiEntropyService.line 813 in cassandra-1.1.2, use Config.phi_convict_threshold:
{code}
            // We want a higher confidence in the failure detection than usual because failing a repair wrongly has a high cost.
            if (phi < 2 * DatabaseDescriptor.getPhiConvictThreshold())
                return;
{code}

where DatabaseDescriptor.getPhiConvictThreshold() returns Conf.phi_convict_threshold.

So, it looks like there are cases where a value is stored in multiple places, and setting the value via JMX doesn't set all of them. I'd say there should only be a single place where a configuration parameter is stored, and that single field:
* should read in the value from cassandra.yaml, optionally falling back to a sane default
* should be the field that the JMX attribute reads and sets, and
* any place that needs the current global setting should get it from that field. However, there could be cases where you read in a global value at the start of a task and keep that value locally until the end of the task.

Also, anything settable via JMX should be volatile or set via a synchronized setter, or else according to the Java memory model other threads may be stuck with the old setting.


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