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From GitBox <...@apache.org>
Subject [GitHub] [incubator-zipkin-brave] pburm commented on a change in pull request #908: Fixes some edge cases around sampler resetting
Date Mon, 13 May 2019 15:59:06 GMT
pburm commented on a change in pull request #908: Fixes some edge cases around sampler resetting
URL: https://github.com/apache/incubator-zipkin-brave/pull/908#discussion_r283418212
 
 

 ##########
 File path: brave/src/main/java/brave/sampler/RateLimitingSampler.java
 ##########
 @@ -55,14 +55,17 @@ public static Sampler create(int tracesPerSecond) {
     long updateAt = nextReset.get();
 
     long nanosUntilReset = -(now - updateAt); // because nanoTime can be negative
-    boolean shouldReset = nanosUntilReset <= 0;
-    if (shouldReset) {
-      if (nextReset.compareAndSet(updateAt, updateAt + NANOS_PER_SECOND)) {
-        usage.set(0);
-      }
+    if (nanosUntilReset <= 0) {
+      // Attempt to move into the next sampling interval.
+      // nanosUntilReset is now invalid regardless of race winner, so we can't sample based
on it.
+      if (nextReset.compareAndSet(updateAt, updateAt + NANOS_PER_SECOND)) usage.set(0);
 
 Review comment:
   Only hole that I see here is that since we are ONLY adding one second to updateAt, when
the sampler is long lived and there have not been any sampling decisions in several seconds......it
will sample at 100% until updateAt has caught up. We forked and added + -(nanosUntilReset)
in addition to NANOS_PER_SECOND when we update updateAt. That might push it too far for somebody's
taste, but it cured the 100% sampling in our implementation.

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