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Date: Sat, 11 Dec 2010 04:46:01 -0500 (EST)
From: "Jukka Zitting (JIRA)" <jira@apache.org>
To: dev@jackrabbit.apache.org
Subject: [jira] Commented: (JCR-2835) Poor performance of ISDESCENDANTNODE
 on SQL 2 queries
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    [ https://issues.apache.org/jira/browse/JCR-2835?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12970436#action_12970436 ] 

Jukka Zitting commented on JCR-2835:
------------------------------------

BTW, when adding new files, remember to always include the Apache license header. I added the header to the new test classes in revision 1044613 to fix the Hudson failure caused by this.

> Poor performance of ISDESCENDANTNODE on SQL 2 queries
> -----------------------------------------------------
>
>                 Key: JCR-2835
>                 URL: https://issues.apache.org/jira/browse/JCR-2835
>             Project: Jackrabbit Content Repository
>          Issue Type: Improvement
>          Components: jackrabbit-core, query
>    Affects Versions: 2.2.0, 2.2.1, 2.3.0
>            Reporter: Serge Huber
>             Fix For: 2.3.0
>
>         Attachments: JCR-2835_PerformanceTests.patch, JCR-2835_Poor_performance_on_ISDESCENDANTNODE_constraint_v1.patch
>
>
> Using the latest source code, I have noticed very bad performance on SQL-2 queries that use the ISDESCENDANTNODE constraint on a large sub-tree. For example, the query : 
> select * from [jnt:news] as news where ISDESCENDANTNODE(news,'/root/site') order by news.[date] desc 
> executes in 600ms 
> select * from [jnt:news] as news order by news.[date] desc
> executes in 4ms
> From looking at the problem in the Yourkit profiler, it seems that the culprit is the constraint building, that uses recursive Lucene searches to build the list of descendant node IDs : 
>     private Query getDescendantNodeQuery(
>             DescendantNode dn, JackrabbitIndexSearcher searcher)
>             throws RepositoryException, IOException {
>         BooleanQuery query = new BooleanQuery();
>         try {
>             LinkedList<NodeId> ids = new LinkedList<NodeId>();
>             NodeImpl ancestor = (NodeImpl) session.getNode(dn.getAncestorPath());
>             ids.add(ancestor.getNodeId());
>             while (!ids.isEmpty()) {
>                 String id = ids.removeFirst().toString();
>                 Query q = new JackrabbitTermQuery(new Term(FieldNames.PARENT, id));
>                 QueryHits hits = searcher.evaluate(q);
>                 ScoreNode sn = hits.nextScoreNode();
>                 if (sn != null) {
>                     query.add(q, SHOULD);
>                     do {
>                         ids.add(sn.getNodeId());
>                         sn = hits.nextScoreNode();
>                     } while (sn != null);
>                 }
>             }
>         } catch (PathNotFoundException e) {
>             query.add(new JackrabbitTermQuery(new Term(
>                     FieldNames.UUID, "invalid-node-id")), // never matches
>                     SHOULD);
>         }
>         return query;
>     }
> In the above example this generates over 2800 Lucene queries, which is the culprit. I wonder if it wouldn't be faster to retrieve the IDs by using the JCR to retrieve the list of child IDs ?
> This was probably also missed because I didn't seem to find any performance tests on this constraint.

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