BUG: Template cache memory exhausted.

[blasvicco]

Description

Memory usage can reach over 250MB caching template.
The function in craftcms/cms/src/services/TemplateCaches.php called includeElementQueryInTemplateCaches can be optimized reducing the memory usage to less than 15 Mb.

Suggestion

    /**
     * Includes an element criteria in any active caches.
     *
     * @param Event $event The 'afterPrepare' element query event
     */
    public function includeElementQueryInTemplateCaches(Event $event)
    {
        // Make sure template caching is enabled
        if ($this->_isTemplateCachingEnabled() === false) {
            return;
        }

        if (!empty($this->_cachedQueries)) {
            /** @var ElementQuery $elementQuery */
            $elementQuery = $event->sender;
            $query = $elementQuery->query;
            $subQuery = $elementQuery->subQuery;
            $customFields = $elementQuery->customFields;
            $elementQuery->query = null;
            $elementQuery->subQuery = null;
            $elementQuery->customFields = null;
            // We need to base64-encode the string so db\Connection::quoteSql() doesn't tweak any of the table/columns names
            $serialized = base64_encode(serialize($elementQuery));
            $elementQuery->query = $query;
            $elementQuery->subQuery = $subQuery;
            $elementQuery->customFields = $customFields;
            $hash = md5($serialized);

            gc_disable(); // disable automatic garbage collector
            foreach ($this->_cachedQueries as &$queries) {
                $queries[$hash] = [
                    $elementQuery->elementType,
                    $serialized
                ];
                gc_collect_cycles();
            }
            $queries = null; // release memory
            unset($queries); // break the binding between variable name and variable content
            gc_enable(); // enabling automatic garbage collector
        }
    }

Steps to reproduce

1. Mesure the memory usage of a non cached request with the enableTemplateCaching = true.

Additional info

• Craft version: 3
• PHP version: 7.0.12