I recently received the following ticket info regarding some caching issues on our magento installation, and have run into some stumbling blocks in diagnosing (thus obviously fixing, as well) the underlying issue:
saving changes to any static content in the admin is no longer invalidating that page in the cache. E.g., editing a few words on the 'About Us' page and saving doesn't change anything on the front end, we'd then need to refresh the entire FPC to see our tiny tweak
...snip...
The way it used to work (a few months back), is that upon saving a change, that page and only that page would update on the front end (taking a little longer to load because the cache for that page was invalidated).
At some point (not sure when), we began needing to flush the entire cache and redis cache for the change to appear, which meant the entire site's cache was cleared and everything loaded slowly (and the db takes a huge womping for a bit).
After a bit of that, we realized we didn't even need to flush the redis cache, as it seemed to make no difference, so we've just been flushing the magento cache after any changes ever since.
...snip...
essentially upon updating the FPC module a while back, redis seems to have been cut out of the process of flushing the cache, so potentially it's been disconnected and may be the culprit.
In attempting to diagnose this problem, I've verified that everything on an applicable magento devdoc seems to be set up correctly between FPC and redis, as far as I can tell. IE app/etc/local.xml has the correct options for an installation not using Zend_Cache.
If anybody has any other ideas, or pointers on documentation that may help further with this issue, I would be very grateful. I seem to be having a bit of an issue locating decent magento documentation, on some issues, on this project. Thanks in advance!
Addendum: contents of local.xml follow
<config>
<global>
<install>
<date><![CDATA[Tue, 12 Aug 2014 09:19:47 +0000]]></date>
</install>
<crypt>
<key>***[redacted]***</key>
</crypt>
<disable_local_modules>false</disable_local_modules>
<resources>
<db>
<table_prefix><![CDATA[]]></table_prefix>
</db>
<default_setup>
<connection>
<host><![CDATA[localhost]]></host>
<username>***[redacted]***</username>
<password>***[redacted]***</password>
<dbname>***[redacted]***</dbname>
<initStatements><![CDATA[SET NAMES utf8]]></initStatements>
<model><![CDATA[mysql4]]></model>
<type><![CDATA[pdo_mysql]]></type>
<pdoType><![CDATA[]]></pdoType>
<active>1</active>
</connection>
</default_setup>
</resources>
<session_save><![CDATA[db]]></session_save>
<redis_session>
<host>127.0.0.1</host>
<port>6379</port>
<password>***[redacted]***</password>
<timeout>2.5</timeout>
<persistent></persistent>
<db>2</db>
<compression_threshold>2048</compression_threshold>
<compression_lib>lzf</compression_lib>
<log_level>1</log_level>
<max_concurrency>6</max_concurrency>
<break_after_frontend>5</break_after_frontend>
<break_after_adminhtml>30</break_after_adminhtml>
<first_lifetime>600</first_lifetime>
<bot_first_lifetime>60</bot_first_lifetime>
<bot_lifetime>7200</bot_lifetime>
<disable_locking>0</disable_locking>
<min_lifetime>60</min_lifetime>
<max_lifetime>2592000</max_lifetime>
</redis_session>
<cache>
<backend>Cm_Cache_Backend_Redis</backend>
<backend_options>
<server>127.0.0.1</server> <!-- or absolute path to unix socket -->
<port>6379</port>
<persistent></persistent>
<database>0</database>
<password>***[redacted]***</password>
<force_standalone>0</force_standalone>
<connect_retries>1</connect_retries>
<automatic_cleaning_factor>0</automatic_cleaning_factor>
<compress_data>1</compress_data>
<compress_tags>1</compress_tags>
<compress_threshold>20480</compress_threshold>
<compression_lib>gzip</compression_lib> <!-- Supports gzip, lzf and snappy -->
</backend_options>
</cache>
<fpc>
<lifetime>86400</lifetime>
<backend>Cm_Cache_Backend_Redis</backend>
<backend_options>
<server>127.0.0.1</server>
<port>6379</port>
<persistent>cache-fpc</persistent>
<database>1</database>
<password>***[redacted]***</password>
<force_standalone>1</force_standalone>
<connect_retries>1</connect_retries>
<lifetimelimit>86400</lifetimelimit>
<read_timeout>10</read_timeout>
<compress_data>1</compress_data>
<compress_tags>1</compress_tags>
<compress_data>gzip</compress_data>
</backend_options>
</fpc>
</global>
<admin>
<routers>
<adminhtml>
<args>
<frontName><![CDATA[admin]]></frontName>
</args>
</adminhtml>
</routers>
</admin>
</config>
