Yii NestedSetBehavior内存使用情况

I use NestedSetBehavior model extension in my project for using db table as a tree.

I wroute example:

    $model = SiteMap()->findAll();
    $log .= $this->debug_memory('used')."<br>";
    $ancestors = null;
    foreach ($model as $item) {
        $ancestors = $item->ancestors()->findAll();
    }
    $log .= $this->debug_memory('used')."<br>";
    echo $log;

(debug_memory source just return friendly memory_get_usage(), $model has 50 items)

The result is:

used: 10525440
used: 15892712

After simple calculation - memory usage increased on 5,24 Mb.

But i must use $item->ancestors()->findAll(); many times in cycle, so my memory increased on 138 Mb. And i get @out of memory error".

I try use unset():

    $model = SiteMap()->findAll();
    $log .= $this->debug_memory('used')."<br>";
    $ancestors = null;
    foreach ($model as $item) {
       $ancestors= $item->ancestors()->findAll();
    }
    $ancestors = null;
    unset($ancestors);
    $log .= $this->debug_memory('used')."<br>";
    echo $log;

But i steel get result:

used: 10525984
used: 15893320

Behavior ancestors function source is:

public function ancestors($depth=null)
{
    $owner=$this->getOwner();
    $db=$owner->getDbConnection();
    $criteria=$owner->getDbCriteria();
    $alias=$db->quoteColumnName($owner->getTableAlias());

    $criteria->mergeWith(array(
        'condition'=>$alias.'.'.$db->quoteColumnName($this->leftAttribute).'<'.$owner->{$this->leftAttribute}.
            ' AND '.$alias.'.'.$db->quoteColumnName($this->rightAttribute).'>'.$owner->{$this->rightAttribute},
        'order'=>$alias.'.'.$db->quoteColumnName($this->leftAttribute),
    ));

    if($depth!==null)
        $criteria->addCondition($alias.'.'.$db->quoteColumnName($this->levelAttribute).'>='.($owner->{$this->levelAttribute}-$depth));

    if($this->hasManyRoots)
    {
        $criteria->addCondition($alias.'.'.$db->quoteColumnName($this->rootAttribute).'='.CDbCriteria::PARAM_PREFIX.CDbCriteria::$paramCount);
        $criteria->params[CDbCriteria::PARAM_PREFIX.CDbCriteria::$paramCount++]=$owner->{$this->rootAttribute};
    }

    return $owner;
}

So, my questions is, why this function use so many memory and why when i unset variable memory is not cleaning?

Comment out the logging in your protected/config/main.php file. (Or wherever you define your configuration settings.)

What you are seeing is likely a result of all the logs being written on each Active Record call, which would explain why unsetting the object doesn't release memory: the memory used isn't in the model, it's in the log.

Try that and report results.

Answer

It's always good to disable the logs (as @willem-renzema already stated) to prevent it from using memory (especially when you're testing for leaks).

However you should call detachBehaviors() on each ancestor in your example code to stop it from leaking memory. It's good conduct to do this for every object instance with attached behaviors before using unset on it to prevent memory leaks from happening. Even when you're not explicitly "unsetting" the object (eg. your variables are moving out of scope).

See https://github.com/yiiext/nested-set-behavior/issues/25 for more info about this issue in NestedSetBehavior.

Also see https://github.com/yiisoft/yii/issues/1329#issuecomment-18729026 for a more general discussion on memory leaks and circular references in PHP and Yii.

Note

You could be tempted to use the a destructor (__destruct()) to handle the detaching of behaviors for you. But in this specific case that won't work because of the destructor rule mentioned here.

"Objects will only free their resources and trigger their __destruct() method when all references are unset. Even when they are in the object... sigh!" - (nox at oreigon dot de, 2009).

This rule won't be satisfied by just using unset on an "ancestor" because the NestedSetBehavior still has a reference to the "ancestor" instance stored in a static array called: $_cached. This reference will only be cleared by destroying the NestedSetBehavior instance itself, which will happen of you call detachBehaviors() on the "owner" object of the behavior.