The query compilation cache is a Map used to cache
parsed query strings.  As a result, most queries are only parsed once in
OpenJPA, and cached thereafter.  You can control the compilation cache through
the 
openjpa.QueryCompilationCache configuration property.  This
property accepts a plugin string (see Section 4, “
            Plugin Configuration
        ”)
describing the Map used to associate query strings and
their parsed form.  This property accepts the following aliases:
		
Table 10.2. Pre-defined aliases
| Alias | Value | Notes | 
|---|---|---|
| true | org.apache.openjpa.util.CacheMap | The default option.  Uses a CacheMapto store compilation data.CacheMapmaintains a fixed number of cache entries, and an
optional soft reference map for entries that are moved out of the LRU space.
So, for applications that have a monotonically increasing number of distinct
queries, this option can be used to ensure that a fixed amount of memory is
used by the cache. | 
| all | org.apache.openjpa.lib.util.ConcurrentHashMap | This is the fastest option, but compilation data is never dropped from the cache, so if you use a large number of dynamic queries, this option may result in ever-increasing memory usage. Note that if your queries only differ in the values of the parameters, this should not be an issue. | 
| false | none | Disables the compilation cache. |