Remove old items in chunks to avoid running out of memory when loading item collection.

Author: janpapenbrock

src/app/code/community/FireGento/AdminMonitoring/Model/Clean.php

@@ -27,9 +27,21 @@
  */
 class FireGento_AdminMonitoring_Model_Clean
 {
-    const XML_PATH_ADMINMONITORING_INTERVAL = 'admin/firegento_adminmonitoring/interval';
+    const XML_PATH_ADMINMONITORING_INTERVAL      = 'admin/firegento_adminmonitoring/interval';
     const XML_PATH_ADMINMONITORING_CLEAN_ENABLED = 'admin/firegento_adminmonitoring/enable_cleaning';
 
+    /**
+     * Clean in chunks.
+     *
+     * CHUNK_SIZE determines the items cleared per chunk.
+     *
+     * CHUNK_RUNS determines the number of chunks cleaned per call to clean()
+     *
+     * I.e. per call of clean(), at most CHUNK_SIZE * CHUNK_RUNS items are cleaned.
+     */
+    const CHUNK_SIZE = 1000;
+    const CHUNK_RUNS = 250;
+
     /**
      * Cronjob method for cleaning the database table.
      *
@@ -63,22 +75,53 @@ public function clean()
             return $this;
         }
 
+        $this->cleanInChunks();
+
+        return $this;
+    }
+
+    /**
+     * Clean the database table for the given interval, usink chunks to avoid memory over-usage.
+     *
+     * @return $this
+     */
+    protected function cleanInChunks()
+    {
+        $numChunks = 0;
+        do {
+            $cleanedItems = $this->cleanChunk();
+        } while ($cleanedItems == static::CHUNK_SIZE && $numChunks++ < static::CHUNK_RUNS);
+
+        return $this;
+    }
+
+    /**
+     * Clean a chunk of the items in database table for the given interval.
+     *
+     * @return int Number of items deleted
+     */
+    protected function cleanChunk()
+    {
         $interval = Mage::getStoreConfig(self::XML_PATH_ADMINMONITORING_INTERVAL);
 
         /* @var $adminMonitoringCollection FireGento_AdminMonitoring_Model_Resource_History_Collection */
         $adminMonitoringCollection = Mage::getModel('firegento_adminmonitoring/history')
             ->getCollection()
+            ->setPageSize(static::CHUNK_SIZE)
             ->addFieldToFilter(
                 'created_at',
                 array(
                     'lt' => new Zend_Db_Expr("DATE_SUB('" . now() . "', INTERVAL " . (int) $interval . " DAY)")
                 )
             );
 
+        $count = 0;
+
         foreach ($adminMonitoringCollection as $history) {
             $history->delete();
+            $count++;
         }
 
-        return $this;
+        return $count;
     }
 }