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Subject [GitHub] [cassandra] aweisberg commented on a change in pull request #283: CASSANDRA-14459: DynamicEndpointSnitch should never prefer latent replicas
Date Fri, 22 Mar 2019 23:29:59 GMT
aweisberg commented on a change in pull request #283: CASSANDRA-14459: DynamicEndpointSnitch
should never prefer latent replicas
URL: https://github.com/apache/cassandra/pull/283#discussion_r268000375
 
 

 ##########
 File path: src/java/org/apache/cassandra/locator/DynamicEndpointSnitch.java
 ##########
 @@ -458,17 +490,38 @@ void scheduleProbes(Map<InetAddressAndPort, AnnotatedMeasurement>
samples)
      * that operates on the latencyProbeExecutor thread and it records the maximum latency
between a small and large
      * message channel ping.
      */
-    private void sendPingMessageToPeer(InetAddressAndPort to)
+    private void sendLatencyProbeToPeer(InetAddressAndPort to)
     {
         // This method may have been scheduled (a long time) before it executes, so have
to do
         // some quick sanity checks before sending a message to this host
         if (!StorageService.instance.isGossipActive() || !Gossiper.instance.isAlive(to))
             return;
 
-        probeRateLimiter.acquire(dynamicSampleUpdateInterval);
+        probeRateLimiter.acquire();
 
+        // We don't have a good way of estimating the localhost latency right now, so instead
we give it
 
 Review comment:
   The latency probes are just a measure of distance, so in the absence of measurements we
measure the  distance and occasionally send a request based on distance to see what the actual
performance is? Seems like we could just measure the time to roundtrip a task through the
read stage and call it good?
   
   Other non-distance measurements don't seem any more valid to me.

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