Currently we get the NodeAssociations from the database for each issue for every association. However, it may be useful to get these all in one database call.

We can cache them in a ThreadLocal, so that subsequent hits to the NodeAssociationManager doesn't incur the database hit. This may also reduce the need for the IssueCache.

From the current entities that we store in that table, it would make sense to cache them all:

insomniac=# select distinct source_node_entity from nodeassociation ;
source_node_entity
--------------------
Issue
Project
(2 rows)

insomniac=# select distinct sink_node_entity from nodeassociation ;
sink_node_entity
-----------------------
Component
IssueTypeScreenScheme
NotificationScheme
PermissionScheme
Version
(5 rows)

insomniac=# select distinct association_type from nodeassociation ;
association_type
------------------
IssueComponent
IssueFixVersion
IssueVersion
ProjectScheme

We should also bound this cache, so that in any thread that hits lots of NodeAssociations, we don't load them all into memory.