What does "invalidated" cache mean in Magento?

Question

In the Magento admin under Cache Management, what does it mean when it shows a cache as invalidated? How does Magento know a cache is invalidated? In particular, I'm wondering about HTML Block cache. What conditions would cause this cache to show up as invalidated?

Answer 1

In Magento, whenever you make changes to products, static blocks, etc, it recognizes that the data in the database is no longer the same as what it has in the cache. Unfortunately, Magento doesn't realize what cache data is different, just that something is different.

You will need to go into System > Cache Management and refresh the invalidated cache types.

EDIT:

Create a module (or use an existing module) that you can use to set up a cron job for refreshing the cache. Create a file: {namespace}/{modulename}/Model/Observer.php

Inside that file:

<?php
class <namespace>_<modulename>_Model_Observer {

  public function refreshCache() {
    try {
      $allTypes = Mage::app()->useCache();
      foreach($allTypes as $type => $blah) {
        Mage::app()->getCacheInstance()->cleanType($type);
      }
    } catch (Exception $e) {
      // do something
      error_log($e->getMessage());
    }
  }

}

In your module's etc/config.xml:

<config>
  ...
  <crontab>
    <jobs>
      <{modulename}_refresh_cache>
        <schedule><cron_expr>* * * * *</cron_expr></schedule>
        <run><model>{modulename}/observer::refreshCache</model></run>
      </{modulename}_refresh_cache>
    </jobs>
  </crontab>
  ...
</config>

Now as long as cron is configured correctly on your server, the cache will update automatically, as often as cron runs.

Answer 2

None of the answers so far provided a correct definition, neither a solution. So I decided to necro-answer :-)

what does it mean when it shows a cache as invalidated?

It means that the cached data does not reflect the actual data from the database. As simple as that.

Now, the important question which wasn't asked is what makes invalidation happen. There are basically two major reasons for this:

• You have a bad code that uses direct SQL queries against the database - this bypasses Magento classes, so it can't know which data is correctly indexed, thus it has to mark entire indexes/caches as invalid.
• Reindexing isn't running. This means that Magento cron is likely not set up. The reindexing is what triggers individual cache entries to be updated. Another sub-reason is that reindexing is set to "On save", then the page was timed out / closed prematurely while saving a product / CMS page, etc.
• The least likely one (but still valid) is a Magento bug or some major settings change that requires a cache to be cleaned in its entirety.

Solutions are:

• Get rid of any plugins (or developers!) which introduce direct SQL queries to your Magento codebase
• Ensure Magento cron is configured and running, ensure that indexes are set to be updated "On Schedule"

A solution like "clean cache which was invalidated" is absolutely gross. That is addressing the symptom instead of the root cause. This comes at the cost of many lost conversions (read = money) because you're essentially running cacheless - for even average stores it may take days to fully recover from a single cache clean and warm up the cache to its full potential.

Answer 3

2015: AOE Sheduler is able to clean the cache by cronjob. Change JOB

"core_clean_cache"

from 30 2 * * * (Daily 2:30) to 59 * * * * (Every 59 Minutes).

Answer 4

The @Magento Guy answer is correct, but I think this solution below can help you on refreshing just the invalidated caches on Magento.

I use Bitnami Magento Stack, for me this solution below was the best I have found.

I've tried to create a Mage_Shell_Class php file, but without success (invalid cache array were always empty when it runs, no matter what, and I really don't imagine why).

I've created a php file 'sample.php':

<?php

require 'app/Mage.php';

$invalid = Mage::app()->getCacheInstance()->getInvalidatedTypes();

foreach($invalid as $i)
{
    Mage::app()->getCacheInstance()->cleanType($i["id"]);
}

I've placed it on magento root folder, and to start it I use a cronjob that runs under root user.

So, to create the cronjob on the root user:

sudo crontab -u root -e

And this was my command line to run it:

* * * * * . /opt/bitnami/scripts/setenv.sh ; /opt/bitnami/php/bin/php /opt/bitnami/apps/magento/htdocs/sample.php >> /var/log/cron/cron.log 2>&1

Some parts on this line are very particular to my problem:

1. Since it just refreshes the invalidated caches I've decided to run it every minute.
2. setenv.sh is a script that helps me to set the environment when dealing with this particular bitnami stack.
3. To get the output of this script I used this last part ">> /var/log/cron/cron.log 2>&1" to output errors to a directory that I've created (/var/log/cron), and has given the correct permissions on it.

Probably you need to change the cron line command, but I think this will help you.