Added adaptive sampling

Author: allflame

src/Sampler/RateLimitingSampler.php

@@ -18,7 +18,8 @@ public function __construct(float $rate, GeneratorInterface $generator)
     public function doDecide(int $tracerId, string $operationName): SamplerResult
     {
         $key = $this->generator->generate($tracerId, $operationName);
-        if (false !== ($current = apcu_add($key, sprintf('%s:%d', time(), 1), 1 / $this->rate))) {
+        $ttl = max((int)(1 / $this->rate + 1), 1);
+        if (false !== ($current = apcu_add($key, sprintf('%s:%d', time(), 1), $ttl))) {
             return new SamplerResult(
                 true, 0x01, [
                         new SamplerTypeTag('ratelimiting'),