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https://issues.apache.org/jira/browse/CASSANDRA-4479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426824#comment-13426824
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Eric Dong commented on CASSANDRA-4479:
--------------------------------------
For comparison, rpc_timeout_in_ms is settable through JMX via
StorageProxy[MBean], but StorageProxy doesn't have its own rpc_timeout_in_ms
field, it calls DatabaseDescriptor.setRpcTimeout(Long), which sets
Conf.rpc_timeout_in_ms. However, Conf.rpc_timeout_in_ms is neither volatile nor
set via a synchronized method, which is still bad.
> 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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