elasticsearch hooks into Lucene eager eviction of caches (based on IndexReader) by overriding the FieldCache class with its own and hacking a listener mechanism. This means that without that, the cached will be cleared based on weak references in the JVM. The message you get happens because lucene jars exists in the classpath before elasticsearch, so the Lucene FieldCache class was loaded, and not the hacked on of elasticsearch.
The good news is that in upcoming Lucene 3.1 there will be a formal cache eviction listener API that elasticsearch will be able to use.
On Wednesday, March 16, 2011 at 12:56 AM, zohar wrote:
when running 0.15.2 we get the following warn : WARN [Anarchist] lucene default FieldCache is used, not enabling eager reader based cache eviction
Could not find this in the docs and would like to understand what this means.