Magento Cache Tags and Debugging

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1. @TONEGOLF71 @SPACE48ERS #MAGETITANS MAGENTO CACHE TAGS AND DEBUGGING ! Tony Brown Technical Director @ Space 48
2. @TONEGOLF71 @SPACE48ERS #MAGETITANS – Wikipedia “Caching is a component that transparently stores data so that future requests for that data can be served faster. ” What is caching?
3. @TONEGOLF71 @SPACE48ERS #MAGETITANS Many types of caching • Browser caching • Reverse proxy (Varnish, NGINX) • Opcode Cache (APC, OPcache) • Application cache (Magento) • Plus many more…
4. @TONEGOLF71 @SPACE48ERS #MAGETITANS Magento Cache
5. @TONEGOLF71 @SPACE48ERS #MAGETITANS Magento Cache • Key-value data store • Data can be tagged with meta data • By default is stored on the filesystem (/var) • Other storage backends can be used • We use Redis (thanks Colin Mollenhour)
6. @TONEGOLF71 @SPACE48ERS #MAGETITANS Magento Cache • Mage_Core_Model_Cache • save($value, $key, $tags = array(), $lifeTime=null) • load($key) • remove($key) • clean($tags = array())
7. @TONEGOLF71 @SPACE48ERS #MAGETITANS Problem • Inherited a Magento store • It had a full page caching (FPC) module in place • It was thought that the FPC was clearing too often
8. @TONEGOLF71 @SPACE48ERS #MAGETITANS Investigation tools • Mage::log() • Xdebug • Redis monitor
9. @TONEGOLF71 @SPACE48ERS #MAGETITANS Replicate the issue • Small perceptible difference in cached versus uncached page loads. • We were told that the cache dropping seemed to coincide with catalog updates • We tested and yes, product saves would wipe the cache?!
10. @TONEGOLF71 @SPACE48ERS #MAGETITANS Diagnose the issue Tags cleared on product save Breakpoint in Mage_Core_Model_Cache on clean()
11. @TONEGOLF71 @SPACE48ERS #MAGETITANS Diagnose the issue Tags associated on product view Breakpoint in Mage_Core_Model_Cache on save()
12. @TONEGOLF71 @SPACE48ERS #MAGETITANS WTF?
13. @TONEGOLF71 @SPACE48ERS #MAGETITANS Diagnose the issue Tags saved on product view Breakpoint in Mage_Core_Model_Cache on save()
14. @TONEGOLF71 @SPACE48ERS #MAGETITANS Diagnose the issue • Eliminate as much as possible as quickly as possible • Go back to a core theme • Disable all non-core modules. • The culprit - A bespoke top-nav replacement module!!!
15. @TONEGOLF71 @SPACE48ERS #MAGETITANS But Why?
16. @TONEGOLF71 @SPACE48ERS #MAGETITANS But why? • model_load_after observer in the FPC module • This collects tags for each model loaded via $object->getCacheIdTags() But WHY??
17. @TONEGOLF71 @SPACE48ERS #MAGETITANS But why? • The bespoke menu navigation module uses Mage::getModel(‘catalog/category’)->load($Id) for each category • Therefore a tag for each category in the menu was added!!!
18. @TONEGOLF71 @SPACE48ERS #MAGETITANS The solution? • Refactor the navigation menu to work in the same way as the core. • i.e use getCategories() from the category resource model
19. @TONEGOLF71 @SPACE48ERS #MAGETITANS In short… • Use Xdebug to check out what your cache tags are doing!
20. @TONEGOLF71 @SPACE48ERS #MAGETITANS THANKS!! tony@space48.com @tonegolf71