Issues

ZF-6161: setDefaultMetadataCache throw exception after restart the memcached

Description


Fatal error: Uncaught exception 'Zend_Db_Table_Exception' with message 'Failed saving metadata to 
metadataCache' in /var/www/ZENDIR/Zend/Db/Table/Abstract.php:635 Stack trace: 
#0 /var/www/ZENDIR/Zend/Db/Table/Abstract.php(540): Zend_Db_Table_Abstract->_setupMetadata() 
#1 /var/www/ZENDIR/Zend/Db/Table/Abstract.php(268): Zend_Db_Table_Abstract->_setup() 
#2 /var/www/prcms/application/Initializer.php(155): Zend_Db_Table_Abstract->__construct() 
#3 /var/www/prcms/application/Initializer.php(55): Initializer->initSite() 
#4 /var/www/prcms/application/bootstrap.php(31): Initializer->__construct('testing') 
#5 /var/www/prcms/public/index.php(2): require('/var/www/prcms/...') 
#6 {main} thrown in /var/www/ZENDIR/Zend/Db/Table/Abstract.php on line 635

ENV: 1) Linux lamp 2.6.18-4-686 #1 SMP Mon Mar 26 17:17:36 UTC 2007 i686 GNU/Linux 2) apache-2.2.6 3) php-5.2.3 4) memcached-1.2.4 (should also affect latest stable version) 5) ZendFramework: 1.6.2 (after checked the latest trunk code, the problem hasnot fixed yet)

Our system use memcached as the cache storage, the connection is persistent. This bug hasnot occured under non-persistent Memcached circumstance

So the description below under persistent connection. (1) After restart the Memcached, function save frequently returns false;


Zend/Db/Table/Abstract.php
            if (null !== $this->_metadataCache && !$this->_metadataCache->save($metadata, $cacheId)) {
                /**
                 * @see Zend_Db_Table_Exception
                 */
                require_once 'Zend/Db/Table/Exception.php';
                throw new Zend_Db_Table_Exception('Failed saving metadata to metadataCache');
            }

So if $this->_metadataCache->save($metadata, $cacheId)) return false, then the exception threw

Comments

Agree. This is not a crit error for Zend_Db_Table and need no exception to throw.

same error if memached is not reachable, throw an exception

Formatted error. Marked as trivial since a suggested fix is supplied. Marked as "should have" for "next mini release"

why isnt this fixed in current versions ?

at least seems this way in 1.9.0

restart memcached error -> reload -> working -> reload -> error

should take a look at the datestamps of the comments... nevermind.

Digging into this, is an exception not what we want here? It seems like if you ask it to use a cache, and the cache fails at saving, shouldnt an exception be thrown? Is this perhaps a situation that should be taken care of before table metadataSetup(), like in the bootstrap? Perhaps the bootstrap should detect if memcached is not available?

-ralph

Is it possible situation when memcached server fails after connection setting up? Yes. In that case if exception will be thrown we'll get unwanted break up. I want to see my scripts still working fine even in the case memcached doesn't work properly.

If we really need to know the cache failed, wouldn't a throw from Zend_Cache be a better place then a throw from Zend_Db?

Alternatively, couldn't it just be a trigger_error(...., Notice) rather then a throw?

Really, notice is the best way to keep a web-master informed about cache subsystem problems and not to interrupt normal code execution later on.

the really strange part of this is the error comes and goes.

Restart memcached -> access the page -> error -> reload -> working -> reload -> working or error

after a few minutes (dont know on what it depends) no errors are thrown.. until the next memcached restart.

What i have to try sometimes is what if you configure more than one memcached server will a error thrown wenn only one of them is restarted.

In general i would also suggest to trigger a notice, a cache failure is not allowed to stop a, besides this, working page.

If the memcached server is not available, it seems like Zend_Cache should throw an exception, no?

Then, when inside Zend_Db_Table, it should treat Zend_Cache as a (effectively) /dev/null cache, thus, it will always have to do the lookup on the metadata.

Or am I missing something?

That's right. Cache should be used to improve the performance of process, should not break the process. The current version, even if we caught the exception thrown within Zend_Db_Table, we can not return to run as no cache.

Patch contains:

Changed throw to E_USER_NOTICE on metaCache save fail Updated test suite to match

I have not been able to find out what's causing the exception to be thrown, I initialise the cache in my bootstrap like this:

protected function _initDbTableCache() { $cache = Zend_Cache::factory('Core', 'File', array('automatic_serialization' => true), array('cache_dir' => APPLICATION_PATH . '/cache') ); Zend_Db_Table_Abstract::setDefaultMetadataCache($cache); }

but every now and then, it throws an exception.

I have the same setup setup as Juraj. Since updating to 10.0.2, a notice is thrown instead of an exception. This is nice, but I don't know why its being thrown. I'm guessing that it throws whenever the cache is old, but I need to setup better logs to see if this is really the case.

Any ideas for pinpointing the problem?

I have a similar problem with memcached as metadatacache. I use the Zend_Session_SaveHandler_DbTable, and from time to time I get an exception saying that saving metadata failed (because Zend_Db_Table is used to save session data). As a result session_start() does not work. See log below.

I will now try to use a "non-persistent" connection to memcached.

I also had the problem in the past with restarting memcached: Restart memcached -> access the page -> error -> reload -> working -> reload -> working or error Since it is not an exception anymore the problem is gone.

{quote}[12-May-2010 10:12:05] PHP Fatal error: Uncaught exception 'Zend_Session_Exception' with message 'Zend_Session::start() - /home/user/workspace/ZendFramework-1.10.3/library/Zend/Db/Table/Abstract.php(Line:826): Error #1024 Failed saving metadata to metadataCache Array' in /home/user/workspace/ZendFramework-1.10.3/library/Zend/Session.php:493 Stack trace:

0 /home/user/workspace/Project/application/Bootstrap.php(286): Zend_Session::start()

1 /home/user/workspace/ZendFramework-1.10.3/library/Zend/Application/Bootstrap/BootstrapAbstract.php(665): Bootstrap->_initSession()

2 /home/user/workspace/ZendFramework-1.10.3/library/Zend/Application/Bootstrap/BootstrapAbstract.php(618): Zend_Application_Bootstrap_BootstrapAbstract->_executeResource('session')

3 /home/user/workspace/ZendFramework-1.10.3/library/Zend/Application/Bootstrap/BootstrapAbstract.php(582): Zend_Application_Bootstrap_BootstrapAbstract->_bootstrap(NULL)

4 /home/user/workspace/Ze in /home/user/workspace/ZendFramework-1.10.3/library/Zend/Session.php on line 493{quote}