Eliminate wlocks when updating existing histograms, gauges (#116)

apcu_add always takes a wlock in the current version 5.1.22, which leads to lots of lock contention in high concurrency scenarios. Since the most common operation ought to be updating an already existing key, wrap apcu_add in an apcu_exists that only takes a rlock. Signed-off-by: Tobias Bengtsson <[email protected]> Co-authored-by: Lukas Kämmerling <[email protected]>
PromPHP · Apr 14, 2023 · 144022e · 144022e
1 parent bf7d43e
commit 144022e
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Showing 2 changed files with 27 additions and 13 deletions.
diff --git a/src/Prometheus/Storage/APC.php b/src/Prometheus/Storage/APC.php
@@ -56,11 +56,13 @@ public function updateHistogram(array $data): void
     {
         // Initialize the sum
         $sumKey = $this->histogramBucketValueKey($data, 'sum');
-        $new = apcu_add($sumKey, $this->toBinaryRepresentationAsInteger(0));
+        if (!apcu_exists($sumKey)) {
+            $new = apcu_add($sumKey, $this->toBinaryRepresentationAsInteger(0));
 
-        // If sum does not exist, assume a new histogram and store the metadata
-        if ($new) {
-            apcu_store($this->metaKey($data), json_encode($this->metaData($data)));
+            // If sum does not exist, assume a new histogram and store the metadata
+            if ($new) {
+                apcu_store($this->metaKey($data), json_encode($this->metaData($data)));
+            }
         }
 
         // Atomically increment the sum
@@ -83,8 +85,11 @@ public function updateHistogram(array $data): void
         }
 
         // Initialize and increment the bucket
-        apcu_add($this->histogramBucketValueKey($data, $bucketToIncrease), 0);
-        apcu_inc($this->histogramBucketValueKey($data, $bucketToIncrease));
+        $bucketKey = $this->histogramBucketValueKey($data, $bucketToIncrease);
+        if (!apcu_exists($bucketKey)) {
+            apcu_add($bucketKey, 0);
+        }
+        apcu_inc($bucketKey);
     }
 
     /**
@@ -94,11 +99,15 @@ public function updateSummary(array $data): void
     {
         // store meta
         $metaKey = $this->metaKey($data);
-        apcu_add($metaKey, $this->metaData($data));
+        if (!apcu_exists($metaKey)) {
+            apcu_add($metaKey, $this->metaData($data));
+        }
 
         // store value key
         $valueKey = $this->valueKey($data);
-        apcu_add($valueKey, $this->encodeLabelValues($data['labelValues']));
+        if (!apcu_exists($valueKey)) {
+            apcu_add($valueKey, $this->encodeLabelValues($data['labelValues']));
+        }
 
         // trick to handle uniqid collision
         $done = false;
@@ -118,9 +127,11 @@ public function updateGauge(array $data): void
             apcu_store($valueKey, $this->toBinaryRepresentationAsInteger($data['value']));
             apcu_store($this->metaKey($data), json_encode($this->metaData($data)));
         } else {
-            $new = apcu_add($valueKey, $this->toBinaryRepresentationAsInteger(0));
-            if ($new) {
-                apcu_store($this->metaKey($data), json_encode($this->metaData($data)));
+            if (!apcu_exists($valueKey)) {
+                $new = apcu_add($valueKey, $this->toBinaryRepresentationAsInteger(0));
+                if ($new) {
+                    apcu_store($this->metaKey($data), json_encode($this->metaData($data)));
+                }
             }
             // Taken from https://github.com/prometheus/client_golang/blob/66058aac3a83021948e5fb12f1f408ff556b9037/prometheus/value.go#L91
             $done = false;

diff --git a/src/Prometheus/Storage/APCng.php b/src/Prometheus/Storage/APCng.php
@@ -113,8 +113,11 @@ public function updateHistogram(array $data): void
         }
 
         // Initialize and increment the bucket
-        apcu_add($this->histogramBucketValueKey($data, $bucketToIncrease), 0);
-        apcu_inc($this->histogramBucketValueKey($data, $bucketToIncrease));
+        $bucketKey = $this->histogramBucketValueKey($data, $bucketToIncrease);
+        if (!apcu_exists($bucketKey)) {
+            apcu_add($bucketKey, 0);
+        }
+        apcu_inc($bucketKey);
     }
 
     /**