This modification for Magento 1.x prevents multiple processes from generating the configuration cache on cold cache, reducing CPU load on frontend web servers.
Add the following settings to your local.xml inside the <global> node:
<global>
...
<cache_lock>
<enable>1</enable> <!-- If cache locking is enabled or not -->
<server>127.0.0.1</server> <!-- The Redis database IP -->
<port>6379</port> <!-- The Redis port -->
<database>0</database> <!-- The Redis Database to use -->
<password></password> <!-- The password of the Redis server -->
<timeout>2.5</timeout> <!-- The Redis timeout -->
<key>cache_lock</key> <!-- The name of lock in the Redis Database -->
<max_attempts>10</max_attempts> <!-- The maximum amount of times to retry the connection. Defaults to 10. -->
<retry_time>10000000</retry_time> <!-- The amount of microseconds to wait between checking the cache has generated. Defaults to 10000000 -->
</cache_lock>
</global>
I first heard about this project at Mage Titans 2015 during a talk by Paul Partington, the slides can be found here.
Thanks to ctidigital for their work on this project. You can find the original repository here.