bug #45896 [Cache] Optimize caching of tags (sbelyshkin)

This PR was merged into the 6.1 branch.

Discussion
----------

[Cache] Optimize caching of tags

| Q             | A
| ------------- | ---
| Branch?       | 6.1
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | - <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT
| Doc PR        | - <!-- required for new features -->

It's the follow-up to #42997.

1. Forcing the adapter to fetch tags on item commits makes the algorithm straightforward and a bit more optimized.
2. Caching tag versions only when they are retrieved from or being persisted to the pool ensures that any tagged item will be rejected when there is no related tags in the pool.
3. Using FIFO instead of LRU for known tag versions allows to use all cached tags until expiration and still be able to prevent memory leak.

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Commits
-------

68f309b [Cache] Optimize caching of tags

src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php

@@ -39,7 +39,6 @@ class TagAwareAdapter implements TagAwareAdapterInterface, TagAwareCacheInterfac
     use LoggerAwareTrait;
 
     public const TAGS_PREFIX = "\0tags\0";
-    private const MAX_NUMBER_OF_KNOWN_TAG_VERSIONS = 1000;
 
     private array $deferred = [];
     private AdapterInterface $pool;
@@ -79,8 +78,7 @@ static function (array $items, array $itemTags) {
         );
         self::$setTagVersions ??= \Closure::bind(
             static function (array $items, array $tagVersions) {
-                $now = null;
-                foreach ($items as $key => $item) {
+                foreach ($items as $item) {
                     $item->newMetadata[CacheItem::METADATA_TAGS] = array_intersect_key($tagVersions, $item->newMetadata[CacheItem::METADATA_TAGS] ?? []);
                 }
             },
@@ -343,14 +341,16 @@ public function __destruct()
     private function getTagVersions(array $tagsByKey, bool $persistTags): array
     {
         $tagVersions = [];
-        $fetchTagVersions = false;
+        $fetchTagVersions = $persistTags;
 
         foreach ($tagsByKey as $tags) {
             $tagVersions += $tags;
-
+            if ($fetchTagVersions) {
+                continue;
+            }
             foreach ($tags as $tag => $version) {
                 if ($tagVersions[$tag] !== $version) {
-                    unset($this->knownTagVersions[$tag]);
+                    $fetchTagVersions = true;
                 }
             }
         }
@@ -364,14 +364,10 @@ private function getTagVersions(array $tagsByKey, bool $persistTags): array
         foreach ($tagVersions as $tag => $version) {
             $tags[$tag.static::TAGS_PREFIX] = $tag;
             $knownTagVersion = $this->knownTagVersions[$tag] ?? [0, null];
-            if ($fetchTagVersions || $knownTagVersion[1] !== $version || $now - $knownTagVersion[0] >= $this->knownTagVersionsTtl) {
-                // reuse previously fetched tag versions up to the ttl
+            if ($fetchTagVersions || $now > $knownTagVersion[0] || $knownTagVersion[1] !== $version) {
+                // reuse previously fetched tag versions until the expiration
                 $fetchTagVersions = true;
             }
-            unset($this->knownTagVersions[$tag]); // For LRU tracking
-            if ([0, null] !== $knownTagVersion) {
-                $this->knownTagVersions[$tag] = $knownTagVersion;
-            }
         }
 
         if (!$fetchTagVersions) {
@@ -380,20 +376,24 @@ private function getTagVersions(array $tagsByKey, bool $persistTags): array
 
         $newTags = [];
         $newVersion = null;
+        $expiration = $now + $this->knownTagVersionsTtl;
         foreach ($this->tags->getItems(array_keys($tags)) as $tag => $version) {
-            if (!$version->isHit()) {
+            unset($this->knownTagVersions[$tag = $tags[$tag]]); // update FIFO
+            if (null !== $tagVersions[$tag] = $version->get()) {
+                $this->knownTagVersions[$tag] = [$expiration, $tagVersions[$tag]];
+            } elseif ($persistTags) {
                 $newTags[$tag] = $version->set($newVersion ??= random_bytes(6));
+                $tagVersions[$tag] = $newVersion;
+                $this->knownTagVersions[$tag] = [$expiration, $newVersion];
             }
-            $tagVersions[$tag = $tags[$tag]] = $version->get();
-            $this->knownTagVersions[$tag] = [$now, $tagVersions[$tag]];
         }
 
-        if ($newTags && $persistTags) {
+        if ($newTags) {
             (self::$saveTags)($this->tags, $newTags);
         }
 
-        if (\count($this->knownTagVersions) > $maxTags = max(self::MAX_NUMBER_OF_KNOWN_TAG_VERSIONS, \count($newTags) << 1)) {
-            array_splice($this->knownTagVersions, 0, $maxTags >> 1);
+        while ($now > ($this->knownTagVersions[$tag = array_key_first($this->knownTagVersions)][0] ?? \INF)) {
+            unset($this->knownTagVersions[$tag]);
         }
 
         return $tagVersions;

src/Symfony/Component/Cache/Tests/Adapter/TagAwareAdapterTest.php

@@ -12,7 +12,6 @@
 namespace Symfony\Component\Cache\Tests\Adapter;
 
 use PHPUnit\Framework\MockObject\MockObject;
-use Psr\Cache\CacheItemInterface;
 use Psr\Cache\CacheItemPoolInterface;
 use Symfony\Component\Cache\Adapter\AdapterInterface;
 use Symfony\Component\Cache\Adapter\ArrayAdapter;
@@ -67,15 +66,18 @@ public function testKnownTagVersionsTtl()
 
         $pool->save($item);
         $this->assertTrue($pool->getItem('foo')->isHit());
-        $this->assertTrue($pool->getItem('foo')->isHit());
 
-        sleep(20);
+        $tagsPool->deleteItem('baz'.TagAwareAdapter::TAGS_PREFIX); // tag invalidation
 
-        $this->assertTrue($pool->getItem('foo')->isHit());
+        $this->assertTrue($pool->getItem('foo')->isHit()); // known tag version is used
 
-        sleep(5);
+        sleep(10);
 
-        $this->assertTrue($pool->getItem('foo')->isHit());
+        $this->assertTrue($pool->getItem('foo')->isHit()); // known tag version is still used
+
+        sleep(1);
+
+        $this->assertFalse($pool->getItem('foo')->isHit()); // known tag version has expired
     }
 
     public function testInvalidateTagsWithArrayAdapter()