Trejkaz created LUCENE-6865:
-------------------------------
Summary: BooleanQuery2ModifierNodeProcessor breaks the query node
hierarchy
Key: LUCENE-6865
URL: https://issues.apache.org/jira/browse/LUCENE-6865
Project: Lucene - Core
Issue Type: Bug
Reporter: Trejkaz
We discovered that one of our own implementations of QueryNodeProcessor was
seeing node.getParent() returning null for nodes other than the root of the
query tree.
I put a diagnostic processor around every processor which runs and found that
BooleanQuery2ModifierNodeProcessor (and possibly others, although it isn't
clear) are mysteriously setting some of the node references to null.
Example query tree before:
{noformat}
GroupQueryNode, parent = null
WithinQueryNode, parent = GroupQueryNode
QuotedFieldQueryNode, parent = WithinQueryNode
GroupQueryNode, parent = WithinQueryNode
AndQueryNode, parent = GroupQueryNode
GroupQueryNode, parent = AndQueryNode
OrQueryNode, parent = GroupQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
GroupQueryNode, parent = AndQueryNode
OrQueryNode, parent = GroupQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
{noformat}
And after BooleanQuery2ModifierNodeProcessor.process():
{noformat}
GroupQueryNode, parent = null
WithinQueryNode, parent = GroupQueryNode
QuotedFieldQueryNode, parent = WithinQueryNode
GroupQueryNode, parent = WithinQueryNode
AndQueryNode, parent = GroupQueryNode
BooleanModifierNode, parent = AndQueryNode
GroupQueryNode, parent = null
OrQueryNode, parent = GroupQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
BooleanModifierNode, parent = AndQueryNode
GroupQueryNode, parent = null
OrQueryNode, parent = GroupQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
QuotedFieldQueryNode, parent = OrQueryNode
{noformat}
Looking at QueryNodeImpl, there is a lot of fiddly logic in there. Removing
children can trigger setting the parent to null, but setting the parent can
also trigger the child removing itself, so it's near impossible to figure out
why this could be happening, but I'm closing in on it at least. My initial
suspicion is that cloneTree() is responsible, because ironically the number of
failures of this sort _increase_ if I try to use cloneTree to defend against
mutability bugs.
The fix I have come up with is to clone the whole API but making QueryNode
immutable. This removes the ability for processors to mess with nodes that
don't belong to them, but also obviates the need for a parent reference in the
first place, which I think is the entire source of the problem - keeping the
parent and child in sync correctly is obviously going to be hard, and indeed we
find that there is at least one bug of this sort lurking in there.
But even if we rewrite it, I figured I would report the issue so that maybe it
can be fixed for others.
Code to use for diagnostics:
{code}
import java.util.List;
import org.apache.lucene.queryparser.flexible.core.QueryNodeException;
import org.apache.lucene.queryparser.flexible.core.config.QueryConfigHandler;
import org.apache.lucene.queryparser.flexible.core.nodes.QueryNode;
import
org.apache.lucene.queryparser.flexible.core.processors.QueryNodeProcessor;
public class DiagnosticQueryNodeProcessor implements QueryNodeProcessor
{
private final QueryNodeProcessor delegate;
public TreeFixingQueryNodeProcessor(QueryNodeProcessor delegate)
{
this.delegate = delegate;
}
@Override
public QueryConfigHandler getQueryConfigHandler()
{
return delegate.getQueryConfigHandler();
}
@Override
public void setQueryConfigHandler(QueryConfigHandler queryConfigHandler)
{
delegate.setQueryConfigHandler(queryConfigHandler);
}
@Override
public QueryNode process(QueryNode queryNode) throws QueryNodeException
{
System.out.println("Before " + delegate.getClass().getSimpleName() +
".process():");
dumpTree(queryNode);
queryNode = delegate.process(queryNode);
System.out.println("After " + delegate.getClass().getSimpleName() +
".process():");
dumpTree(queryNode);
return queryNode;
}
private void dumpTree(QueryNode queryNode)
{
dumpTree(queryNode, "");
}
private void dumpTree(QueryNode queryNode, String prefix)
{
System.out.println(prefix + queryNode.getClass().getSimpleName() +
", parent = " + (queryNode.getParent() == null ?
"null" : queryNode.getParent().getClass().getSimpleName()));
List<QueryNode> children = queryNode.getChildren();
if (children != null)
{
String childPrefix = " " + prefix;
for (QueryNode child : children)
{
dumpTree(child, childPrefix);
}
}
}
}
{code}
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