Dispatcher cache files are updated unexpectedly | AEM

Look for a pattern by collecting the logs about the cache invalidation requests and the content requests. Check for the 3 different scenarios in the Resolution section.

Description description

Environment

Adobe Experience Manager (AEM)

Issue

Sometimes Dispatcher cache files are updated at an unexpected time or frequency.

Resolution resolution

Upon publishing content, Adobe Experience Manager (AEM) sends a cache invalidation request (GET /dispatcher/invalidate.cache) to the Dispatcher. After that, when a request for the content comes to the Dispatcher, it updates its cache files.

Based on this behavior, look for a pattern by collecting the logs about the cache invalidation requests and the content requests.

Example logs for an invalidation request:
Dispatcher - access_log

127.0.0.1 - - [ 07/Jun/2022:13:44:35 +0900]  "GET /dispatcher/invalidate.cache HTTP/1.1" 200 13 "about:blank" "Jakarta Commons-HttpClient/3.1"

Dispatcher - dispatcher.log

[ 07/Jun/2022:13:44:35 +0900]  "GET /dispatcher/invalidate.cache HTTP/1.1" 200 purge [ publish/-]  0ms

Publish - error.log

07.06.2022 13:44:35.750 *INFO* [ sling-threadpool-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx-(apache-sling-job-thread-pool)-1-com_day_cq_replication_job_flush(com/day/cq/replication/job/flush)]  com.day.cq.replication.Agent.flush Sending GET request to http://localhost:80/dispatcher/invalidate.cache
...
07.06.2022 13:44:35.758 *INFO* [ sling-threadpool-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx-(apache-sling-job-thread-pool)-1-com_day_cq_replication_job_flush(com/day/cq/replication/job/flush)]  com.day.cq.replication.Agent.flush Replication (ACTIVATE) of /content/xx-xxxxxx/us/en/products successful.

Cause

Here are typical cases where the Dispatcher cache files are updated unexpectedly.


Case 1 - Frequent cache updates for unexpected contents

Cache files are updated frequently, but the updated contents are not the target of the cache invalidation request.

In this case, the value of /statfileslevel in the Dispatcher configuration may be too low. Note that, commenting out /statfileslevel in dispatcher.any means “0” for this value.

When you have /statfileslevel "0" and publish content, all the cache files are invalidated regardless of the paths. The link in the AEM Dispatcher Guide below describes the detail:

Configuring Dispatcher - Invalidating Files by Folder Level


Case 2 - Cache invalidation requests from an undesired client

The Dispatcher configuration may not have an appropriate restriction for cache invalidation requests. Check /allowedClients in dispatcher.any.


Case 3 - No cache invalidation requests

The Dispatcher configuration may use time-based cache invalidation. In this case, /enableTTL "1" should exist in dispatcher.any.