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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