add a test and workaround

Closes #3505356

src/Cache/CacheBase.php

@@ -127,6 +127,16 @@ abstract class CacheBase implements CacheBackendInterface {
     $this->setPermTtl();
   }
 
+  /**
+   * Returns the CID for the last write timestamp cache.
+   *
+   * @return string
+   *   The last write timestamp CID.
+   */
+  public function getLastWriteCid(): string {
+    return ChainedFastBackend::LAST_WRITE_TIMESTAMP_PREFIX . 'cache_' . $this->bin;
+  }
+
   /**
    * Checks whether the cache id is the last write timestamp.
    *
@@ -142,7 +152,7 @@ abstract class CacheBase implements CacheBackendInterface {
    * @return bool
    */
   protected function isLastWriteTimestamp(string $cid): bool {
-    return $cid === ChainedFastBackend::LAST_WRITE_TIMESTAMP_PREFIX . 'cache_' . $this->bin;
+    return $cid === $this->getLastWriteCid();
   }
 
   /**
@@ -488,6 +498,9 @@ abstract class CacheBase implements CacheBackendInterface {
     usleep(1000);
     $this->lastDeleteAll = round(microtime(TRUE), 3);
     $this->client->set($this->getKey(static::LAST_DELETE_ALL_KEY), $this->lastDeleteAll);
+
+    // Also delete the last write timestamp in case the bin is accessed directly.
+    $this->client->del($this->getPrefix() . ':' . $this->getLastWriteCid());
   }
 
 }