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keepDataAfterExpired and loader exceptions

See original GitHub issue

After deploying cache2k with a loader that always threw an exception, we experienced an OOM.

We originally had set keepDataAfterExpired=true (in combination with refreshAhead=true), with the desire to allow stale data to remain in the cache. Java docs:

  /**
   * Expired data is kept in the cache until the entry is evicted. This consumes memory,
   * but if the data is accessed again the previous data can be used by the cache loader
   * for optimizing (e.g. if-modified-since for a HTTP request). Default value: {@code false}
   *
   * @see AdvancedCacheLoader
   */

Unfortunately, when this is true, Cache2k appears to cache exceptions, which was completely unexpected (is this clearly documented somewhere?) Additionally, the default ExceptionPropagator appends a message to the original exception. These two behaviors combined lead to a cache entry that is an ever-growing exception so long as the cache loader continues to fail, eventually causing OOM.

Is there anyway to prevent exceptions from being cached? Our two options appear to be: keepDataAfterExpired=false (undesired), or provide a custom ExceptionPropagator that does not infinitely grow entries that contain exceptions.

An example exception (stored in the cache as an entry) that continued to grow:

! Causing: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:27:41.064, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:26:41.806, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:26:40.806, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:26:11.536, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:26:10.536, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:23:11.242, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:23:10.242, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:19:40.977, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:19:39.977, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:16:40.675, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:16:39.675, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:13:40.416, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:13:39.416, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:12:10.085, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:12:09.084, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:10:09.8, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:10:08.8, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:09:39.612, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:09:38.612, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:07:09.318, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:07:08.318, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:03:39.045, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:03:38.044, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:00:08.652, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 18:00:07.652, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:56:38.384, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:56:37.383, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:53:08.021, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:53:07.021, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:49:37.739, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:49:36.739, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:46:37.414, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:46:36.414, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:43:07.056, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:43:06.055, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:40:06.768, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:40:05.768, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:39:36.519, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:39:35.519, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:39:16.288, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:39:15.288, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:38:45.993, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:38:44.992, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:37:45.761, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:37:44.761, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:36:45.508, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:36:44.508, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:33:45.112, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:33:44.112, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:30:44.741, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:30:43.741, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:30:14.446, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:30:13.446, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:29:14.148, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:29:13.148, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:28:43.846, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:28:42.846, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:28:13.585, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:28:12.584, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:27:43.276, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:27:42.276, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:27:12.961, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:27:11.961, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:26:12.589, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:26:11.589, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:25:42.218, cause: org.cache2k.integration.CacheLoaderException: expiry=2020-10-19 17:25:41.218, cause: java.lang.RuntimeException:

Issue Analytics

State:
Created 3 years ago
Comments:10 (7 by maintainers)

Top GitHub Comments

1reaction

cruftexcommented, Oct 30, 2020

@rene-m-hernandez No worries. Thanks for the feedback!

Using getValue in the loader is indeed an unfortunate pitfall. Code that does that will work perfectly until an exception happens and then never recover.

Ideas:

Add behavior that detects a CacheLoaderException coming from a loader with the same cause then currently in the entry and replace it with CyclicCacheLoaderException and hinder it from appending.

Maybe don’t call the loader with an entry if the entry has an exception. Probably every loader would ignore the exception anyways and do the same as no previous value is available. That’s a bit inconsistent with the rest of the cache, however, in the context of the loader it makes sense. The whole resilience concept is about making the application more robust. This pitfall actually would lead to the exactly opposite. The application might fail completely from just one exception.

0reactions

cruftexcommented, Nov 24, 2020

Delivered and released as preview: https://github.com/cache2k/cache2k/releases/tag/v1.9.2.Alpha

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