Removed "MAGE" cache tag

[fballiano]

This PR implements the suggestions discussed in #1226 and fixes it.

The MAGE cache tag is only used in order to be able to flush all cache without actually flushing the whole cache storage and since sharing the cache storage with another project/software/whatever would be a very bad practice, we can think about safely remove it.

Removing it will allow for less cache storage space usage and less data to process.

Questions that need to be answered 1

magento-lts/app/code/core/Mage/Admin/Model/Resource/Variable.php

Lines 31 to 43 in e464b27

	protected function _generateCache()
	{
	/** @var Mage_Admin_Model_Resource_Variable_Collection $collection */
	$collection = Mage::getResourceModel('admin/variable_collection');
	$collection->addFieldToFilter('is_allowed', ['eq' => 1]);
	$data = $collection->getColumnValues('variable_name');
	$data = array_flip($data);
	Mage::app()->saveCache(
	Mage::helper('core')->jsonEncode($data),
	self::CACHE_ID,
	[Mage_Core_Model_App::CACHE_TAG]
	);
	}

This method only uses Mage_Core_Model_App::CACHE_TAG as cache tag, what are we doing with that method?

Questions that need to be answered 2

magento-lts/app/code/core/Mage/Admin/Model/Resource/Block.php

Lines 59 to 75 in e464b27

	protected function _generateCache()
	{
	/** @var Mage_Admin_Model_Resource_Block_Collection $collection */
	$collection = Mage::getResourceModel('admin/block_collection');
	$collection->addFieldToFilter('is_allowed', ['eq' => 1]);
	$disallowedBlockNames = $this->getDisallowedBlockNames();
	if (is_array($disallowedBlockNames) && count($disallowedBlockNames) > 0) {
	$collection->addFieldToFilter('block_name', ['nin' => $disallowedBlockNames]);
	}
	$data = $collection->getColumnValues('block_name');
	$data = array_flip($data);
	Mage::app()->saveCache(
	Mage::helper('core')->jsonEncode($data),
	self::CACHE_ID,
	[Mage_Core_Model_App::CACHE_TAG]
	);
	}

same thing as before

Questions that need to be answered 3

magento-lts/app/code/core/Mage/Core/Model/Cache.php

Lines 421 to 434 in e464b27

	public function clean($tags = [])
	{
	$mode = Zend_Cache::CLEANING_MODE_MATCHING_ANY_TAG;
	if (!empty($tags)) {
	if (!is_array($tags)) {
	$tags = [$tags];
	}
	$res = $this->getFrontend()->clean($mode, $this->_tags($tags));
	} else {
	$res = $this->getFrontend()->clean($mode, [Mage_Core_Model_App::CACHE_TAG]);
	$res = $res && $this->getFrontend()->clean($mode, [Mage_Core_Model_Config::CACHE_TAG]);
	}
	return $res;
	}

do we just replace this method with the flush() method?

Fixed Issues

1. Fixes Remove "MAGE" cache tag #1226

[colinmollenhour]

This method only uses Mage_Core_Model_App::CACHE_TAG as cache tag, what are we doing with that method?

Ideally they are associated with a cache type, I'd say either config (Mage_Core_Model_Config::CACHE_TAG) or collections (Mage_Core_Model_Resource_Db_Collection_Abstract::CACHE_TAG) or add a new tag or cache type.

do we just replace this method with the flush() method?

Personally I think flush() should be used since this is fast and won't leak any untagged entries, but if some are opposed to that I think looping over the types would also work:

foreach ($this->getTypes() as $type => $flag) {
    $this->cleanType($type);
}

[fballiano]

all done, thanks @colinmollenhour as usual!

I think this is ready for review now

[sreichel]

Merged latest into #3248 and see ...

FAILED
ERROR: Warning: Undefined variable $res  in /var/www/html/app/code/core/Mage/Core/Model/Cache.php on line 426

[fballiano]

can't reproduce this problem with "main" and developer_mode on, how do you find it?

[sreichel]

Not at home atm ... run clean() method from script or test my ddev command.

$res is not set ...

[fballiano]

true, PR coming in 3 seconds