Unfortunately we have the data cache turned off - we use fetch groups fairly heavily, and we've found that they do not play well with the data cache (https://issues.apache.org/jira/browse/OPENJPA-1280 for instance).
Another issue I found that complicated my situation was our class structure - the hierarchical entity consisted of a superclass and two subclasses, and OpenJPA doesn't do eager fetching of subclass fields. When I flattened them into a single class, the number of SQL queries was cut in half. ________________________________________ From: Henno Vermeulen <he...@huizemolenaar.nl> Sent: Monday, July 21, 2014 1:22 AM To: users@openjpa.apache.org Subject: RE: Avoiding N+1 on collection in recursive relation I did find a workaround for this issue. It's idea can also be used to work around some other performance issues in JPA. The main idea is to efficiently prefetch any entity that OpenJPA would otherwise fetch with single find-by-id queries. Turn on OpenJPA trace and find out which entities are separately selected. Write a query that fetches exactly these entities. Then when performing the main query, OpenJPA will find these from the EntityManager cache. See also my comment on https://issues.apache.org/jira/browse/OPENJPA-2299 Unfortunately this workaround is a bit brittle because it depends on OpenJPA behavior that may change, in particular your query will depend on the fact that only the entities of the second list in the Java code of the entity suffers from this problem, not the first list. Note that the problem I had in OPENJPA-2299 does not have a tree structure. Fetching (sub)trees with JPA also suffers from N+1 select problems, but I don't think that these are directly related to your and my issue described here. These are for the nodes themselves, not for other entities they refer to. But for tree structures you CAN use a similar idea to efficiently fetch a full tree: make a query that fetches all of the nodes, then query for the root node. See also http://www.tikalk.com/java/load-a-tree-with-jpa-and-hibernate Met vriendelijke groet, Henno Vermeulen +31-6-50643787 Paushuize | Kromme Nieuwegracht 49 | 3512 HE Utrecht Huize Molenaar | Korte Nieuwstraat 6 | 3512 NM Utrecht -- _____________ David Minor
