stoty commented on code in PR #1431:
URL: https://github.com/apache/phoenix/pull/1431#discussion_r861979379
##########
phoenix-core/src/main/java/org/apache/phoenix/monitoring/MetricUtil.java:
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@@ -38,4 +46,22 @@ public static MetricsStopWatch getMetricsStopWatch(boolean
isRequestMetricsEnabl
return new MetricsStopWatch(true);
}
+ // We need to cover the case when JmxCacheBuster has just stopped the
HBase metrics
+ // system, and not accidentally overwrite the DefaultMetricsSystem
singleton.
+ // See PHOENIX-6699
+ public static boolean isDefaultMetricsInitialized() {
+ try {
+ MetricsSystemImpl metrics = (MetricsSystemImpl)
DefaultMetricsSystem.instance();
+ Field prefixField =
MetricsSystemImpl.class.getDeclaredField("prefix");
Review Comment:
_MetricsSystemImpl.monitoring_ is not useful for this purpose, as it is set
to false when the metrics system is stopped.
This is why we can overwrite the stopped Default Metrics System:
https://github.com/apache/hadoop/blob/7bd7725532fd139d2e0e1662df7700f7ab95067a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java#L156
_MetricsSystemImpl.prefix_ is only written by the init() method, it is not
touched otherwise, so it can be used to check for the codition when the
MetricsSystemImpl is initialized, but in a stopped state:
https://github.com/apache/hadoop/blob/7bd7725532fd139d2e0e1662df7700f7ab95067a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java#L154
I don't think we have to worry about a race around prefix, AFAICT by the
time the Phoenix classes are loaded, HBase has long initialized DefaultMetrics,
and prefix has been set.
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