RefDataLmdbEnv getLmdbEnvironment() {
        return lmdbEnvironment;
    }
An Off Heap implementation of {@link RefDataStore} using LMDB.
<p>
Essentially each ref stream (a {@link RefStreamDefinition}) contains 1-* map names.
Multiple ref streams can contain the same map name.
Within a ref stream + map combo (a {@link MapDefinition}) there are 1-* entries.
A lookup is done by creating a key that is the lookup key combined with a {@link MapDefinition}
so only an entry matching the lookup key, the map name and the ref stream will be returned.
stroom-pipeline/src/main/java/stroom/pipeline/refdata/store/offheapstore/RefDataOffHeapStore.java