fix for APCng prometheus storage - 0 ttl for entries does not work well with apcu entry expiration algorithm when low global ttl is set, entry ttl needs to be very high

Signed-off-by: Rastusik <mfris@pixelfederation.com>

Author: Rastusik

src/Prometheus/Storage/APCng.php

@@ -18,6 +18,11 @@ class APCng implements Adapter
 
     private const MAX_LOOPS = 10;
 
+    /**
+     * @var int ttl for all apcu entries reserved for prometheus
+     */
+    private $ttl;
+
     /**
      * @var int
      */
@@ -44,10 +49,11 @@ class APCng implements Adapter
      * APCng constructor.
      *
      * @param string $prometheusPrefix Prefix for APCu keys (defaults to {@see PROMETHEUS_PREFIX}).
+     * @param int $ttl ttl for all apcu entries reserved for prometheus, default is 120 days
      *
      * @throws StorageException
      */
-    public function __construct(string $prometheusPrefix = self::PROMETHEUS_PREFIX, int $decimalPrecision = 3)
+    public function __construct(string $prometheusPrefix = self::PROMETHEUS_PREFIX, int $ttl = 10368000, int $decimalPrecision = 3)
     {
         if (!extension_loaded('apcu')) {
             throw new StorageException('APCu extension is not loaded');
@@ -61,6 +67,8 @@ public function __construct(string $prometheusPrefix = self::PROMETHEUS_PREFIX,
         $this->metaInfoCounterKey = implode(':', [ $this->prometheusPrefix, 'metainfocounter' ]);
         $this->metaInfoCountedMetricKeyPattern = implode(':', [ $this->prometheusPrefix, 'metainfocountedmetric_#COUNTER#' ]);
 
+        $this->ttl = $ttl;
+
         if ($decimalPrecision < 0 || $decimalPrecision > 6) {
             throw new UnexpectedValueException(
                 sprintf('Decimal precision %d is not from interval <0;6>.', $decimalPrecision)
@@ -96,7 +104,7 @@ public function updateHistogram(array $data): void
 
         if ($old === false) {
             // If sum does not exist, initialize it, store the metadata for the new histogram
-            apcu_add($sumKey, 0, 0);
+            apcu_add($sumKey, 0, $this->ttl);
             $this->storeMetadata($data);
             $this->storeLabelKeys($data);
         }
@@ -113,7 +121,7 @@ public function updateHistogram(array $data): void
         }
 
         // Initialize and increment the bucket
-        apcu_add($this->histogramBucketValueKey($data, $bucketToIncrease), 0);
+        apcu_add($this->histogramBucketValueKey($data, $bucketToIncrease), 0, $this->ttl);
         apcu_inc($this->histogramBucketValueKey($data, $bucketToIncrease));
     }
 
@@ -134,7 +142,7 @@ public function updateSummary(array $data): void
     {
         // store value key; store metadata & labels if new
         $valueKey = $this->valueKey($data);
-        $new = apcu_add($valueKey, $this->encodeLabelValues($data['labelValues']), 0);
+        $new = apcu_add($valueKey, $this->encodeLabelValues($data['labelValues']), $this->ttl);
         if ($new) {
             $this->storeMetadata($data, false);
             $this->storeLabelKeys($data);
@@ -167,7 +175,7 @@ public function updateGauge(array $data): void
     {
         $valueKey = $this->valueKey($data);
         if ($data['command'] === Adapter::COMMAND_SET) {
-            apcu_store($valueKey, $this->convertToIncrementalInteger($data['value']), 0);
+            apcu_store($valueKey, $this->convertToIncrementalInteger($data['value']), $this->ttl);
             $this->storeMetadata($data);
             $this->storeLabelKeys($data);
 
@@ -177,7 +185,7 @@ public function updateGauge(array $data): void
         $old = apcu_fetch($valueKey);
 
         if ($old === false) {
-            apcu_add($valueKey, 0, 0);
+            apcu_add($valueKey, 0, $this->ttl);
             $this->storeMetadata($data);
             $this->storeLabelKeys($data);
         }
@@ -199,7 +207,7 @@ public function updateCounter(array $data): void
         $old = apcu_fetch($valueKey);
 
         if ($old === false) {
-            apcu_add($valueKey, 0, 0);
+            apcu_add($valueKey, 0, $this->ttl);
             $this->storeMetadata($data);
             $this->storeLabelKeys($data);
         }
@@ -253,7 +261,7 @@ private function addItemToKey(string $key, string $item): void
         $_item = $this->encodeLabelKey($item);
         if (!array_key_exists($_item, $arr)) {
             $arr[$_item] = 1;
-            apcu_store($key, $arr, 0);
+            apcu_store($key, $arr, $this->ttl);
         }
     }
 
@@ -335,7 +343,7 @@ private function scanAndBuildMetainfoCache(): array
             $arr[$type][] = ['key' => $metaKey, 'value' => $metaInfo];
         }
 
-        apcu_store($this->metainfoCacheKey, $arr, 0);
+        apcu_store($this->metainfoCacheKey, $arr, $this->ttl);
 
         return $arr;
     }
@@ -892,17 +900,17 @@ private function storeMetadata(array $data, bool $encoded = true): void
             $toStore = json_encode($metaData);
         }
 
-        $stored = apcu_add($metaKey, $toStore, 0);
+        $stored = apcu_add($metaKey, $toStore, $this->ttl);
 
         if (!$stored) {
             return;
         }
 
-        apcu_add($this->metaInfoCounterKey, 0, 0);
+        apcu_add($this->metaInfoCounterKey, 0, $this->ttl);
         $counter = apcu_inc($this->metaInfoCounterKey);
 
         $newCountedMetricKey = $this->metaCounterKey($counter);
-        apcu_store($newCountedMetricKey, $metaKey, 0);
+        apcu_store($newCountedMetricKey, $metaKey, $this->ttl);
     }
 
     private function metaCounterKey(int $counter): string