SOLR-8925: Add gatherNodes Streaming Expression to support breadth first traversals

solr/core/src/java/org/apache/solr/handler/StreamHandler.java

@@ -28,6 +28,7 @@ import java.util.Map.Entry;
 import org.apache.solr.client.solrj.io.SolrClientCache;
 import org.apache.solr.client.solrj.io.Tuple;
 import org.apache.solr.client.solrj.io.comp.StreamComparator;
+import org.apache.solr.client.solrj.io.graph.GatherNodesStream;
 import org.apache.solr.client.solrj.io.graph.ShortestPathStream;
 import org.apache.solr.client.solrj.io.ops.ConcatOperation;
 import org.apache.solr.client.solrj.io.ops.DistinctOperation;
@@ -117,11 +118,10 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
       .withFunctionName("outerHashJoin", OuterHashJoinStream.class)
       .withFunctionName("intersect", IntersectStream.class)
       .withFunctionName("complement", ComplementStream.class)
-      .withFunctionName("daemon", DaemonStream.class)
        .withFunctionName("sort", SortStream.class)
-      
+         .withFunctionName("daemon", DaemonStream.class)
-      // graph streams
          .withFunctionName("shortestPath", ShortestPathStream.class)
+         .withFunctionName("gatherNodes", GatherNodesStream.class)
 
       // metrics
       .withFunctionName("min", MinMetric.class)
@@ -274,6 +274,14 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
 
     public Tuple read() {
       String msg = e.getMessage();
+
+      Throwable t = e.getCause();
+      while(t != null) {
+        msg = t.getMessage();
+        t = t.getCause();
+      }
+
+
       Map m = new HashMap();
       m.put("EOF", true);
       m.put("EXCEPTION", msg);

solr/solrj/src/java/org/apache/solr/client/solrj/io/graph/GatherNodesStream.java

@@ -0,0 +1,580 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.client.solrj.io.graph;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
+import java.util.HashSet;
+import java.util.ArrayList;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+
+import org.apache.solr.client.solrj.io.eq.MultipleFieldEqualitor;
+import org.apache.solr.client.solrj.io.stream.*;
+import org.apache.solr.client.solrj.io.stream.metrics.*;
+import org.apache.solr.client.solrj.io.Tuple;
+import org.apache.solr.client.solrj.io.comp.StreamComparator;
+import org.apache.solr.client.solrj.io.eq.FieldEqualitor;
+import org.apache.solr.client.solrj.io.stream.expr.Expressible;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpressionNamedParameter;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpressionParameter;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpressionValue;
+import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+import org.apache.solr.common.util.ExecutorUtil;
+import org.apache.solr.common.util.SolrjNamedThreadFactory;
+
+public class GatherNodesStream extends TupleStream implements Expressible {
+
+  private String zkHost;
+  private String collection;
+  private StreamContext streamContext;
+  private Map queryParams;
+  private String traverseFrom;
+  private String traverseTo;
+  private String gather;
+  private boolean trackTraversal;
+  private boolean useDefaultTraversal;
+
+  private TupleStream tupleStream;
+  private Set<Traversal.Scatter> scatter;
+  private Iterator<Tuple> out;
+  private Traversal traversal;
+  private List<Metric> metrics;
+
+  public GatherNodesStream(String zkHost,
+                           String collection,
+                           TupleStream tupleStream,
+                           String traverseFrom,
+                           String traverseTo,
+                           String gather,
+                           Map queryParams,
+                           List<Metric> metrics,
+                           boolean trackTraversal,
+                           Set<Traversal.Scatter> scatter) {
+
+    init(zkHost,
+        collection,
+        tupleStream,
+        traverseFrom,
+        traverseTo,
+        gather,
+        queryParams,
+        metrics,
+        trackTraversal,
+        scatter);
+  }
+
+  public GatherNodesStream(StreamExpression expression, StreamFactory factory) throws IOException {
+
+
+    String collectionName = factory.getValueOperand(expression, 0);
+    List<StreamExpressionNamedParameter> namedParams = factory.getNamedOperands(expression);
+    StreamExpressionNamedParameter zkHostExpression = factory.getNamedOperand(expression, "zkHost");
+
+    List<StreamExpression> streamExpressions = factory.getExpressionOperandsRepresentingTypes(expression, Expressible.class, TupleStream.class);
+    // Collection Name
+    if(null == collectionName) {
+      throw new IOException(String.format(Locale.ROOT,"invalid expression %s - collectionName expected as first operand",expression));
+    }
+
+
+    Set<Traversal.Scatter> scatter = new HashSet();
+
+    StreamExpressionNamedParameter scatterExpression = factory.getNamedOperand(expression, "scatter");
+
+    if(scatterExpression == null) {
+      scatter.add(Traversal.Scatter.LEAVES);
+    } else {
+      String s =  ((StreamExpressionValue)scatterExpression.getParameter()).getValue();
+      String[] sArray = s.split(",");
+      for(String sv : sArray) {
+        sv = sv.trim();
+        if(Traversal.Scatter.BRANCHES.toString().equalsIgnoreCase(sv)) {
+          scatter.add(Traversal.Scatter.BRANCHES);
+        } else if (Traversal.Scatter.LEAVES.toString().equalsIgnoreCase(sv)) {
+          scatter.add(Traversal.Scatter.LEAVES);
+        }
+      }
+    }
+
+    String gather = null;
+    StreamExpressionNamedParameter gatherExpression = factory.getNamedOperand(expression, "gather");
+
+    if(gatherExpression == null) {
+      throw new IOException(String.format(Locale.ROOT,"invalid expression %s - from param is required",expression));
+    } else {
+      gather = ((StreamExpressionValue)gatherExpression.getParameter()).getValue();
+    }
+
+    String traverseFrom = null;
+    String traverseTo = null;
+    StreamExpressionNamedParameter edgeExpression = factory.getNamedOperand(expression, "walk");
+
+    TupleStream stream = null;
+
+    if(edgeExpression == null) {
+      throw new IOException(String.format(Locale.ROOT,"invalid expression %s - walk param is required", expression));
+    } else {
+      if(streamExpressions.size() > 0) {
+        stream = factory.constructStream(streamExpressions.get(0));
+        String edge = ((StreamExpressionValue) edgeExpression.getParameter()).getValue();
+        String[] fields = edge.split("->");
+        if (fields.length != 2) {
+          throw new IOException(String.format(Locale.ROOT, "invalid expression %s - walk param separated by an -> and must contain two fields", expression));
+        }
+        traverseFrom = fields[0].trim();
+        traverseTo = fields[1].trim();
+      } else {
+        String edge = ((StreamExpressionValue) edgeExpression.getParameter()).getValue();
+        String[] fields = edge.split("->");
+        if (fields.length != 2) {
+          throw new IOException(String.format(Locale.ROOT, "invalid expression %s - walk param separated by an -> and must contain two fields", expression));
+        }
+
+        String[] rootNodes = fields[0].split(",");
+        List<String> l = new ArrayList();
+        for(String n : rootNodes) {
+          l.add(n.trim());
+        }
+
+        stream = new NodeStream(l);
+        traverseFrom = "node";
+        traverseTo = fields[1].trim();
+      }
+    }
+
+    List<StreamExpression> metricExpressions = factory.getExpressionOperandsRepresentingTypes(expression, Expressible.class, Metric.class);
+    List<Metric> metrics = new ArrayList();
+    for(int idx = 0; idx < metricExpressions.size(); ++idx){
+      metrics.add(factory.constructMetric(metricExpressions.get(idx)));
+    }
+
+    boolean trackTraversal = false;
+
+    StreamExpressionNamedParameter trackExpression = factory.getNamedOperand(expression, "trackTraversal");
+
+    if(trackExpression != null) {
+      trackTraversal = Boolean.parseBoolean(((StreamExpressionValue) trackExpression.getParameter()).getValue());
+    } else {
+      useDefaultTraversal = true;
+    }
+
+    StreamExpressionNamedParameter scopeExpression = factory.getNamedOperand(expression, "localScope");
+
+    if(trackExpression != null) {
+      trackTraversal = Boolean.parseBoolean(((StreamExpressionValue) trackExpression.getParameter()).getValue());
+    }
+
+    Map<String,String> params = new HashMap<String,String>();
+    for(StreamExpressionNamedParameter namedParam : namedParams){
+      if(!namedParam.getName().equals("zkHost") &&
+          !namedParam.getName().equals("gather") &&
+          !namedParam.getName().equals("walk") &&
+          !namedParam.getName().equals("scatter") &&
+          !namedParam.getName().equals("trackTraversal"))
+      {
+        params.put(namedParam.getName(), namedParam.getParameter().toString().trim());
+      }
+    }
+
+    // zkHost, optional - if not provided then will look into factory list to get
+    String zkHost = null;
+    if(null == zkHostExpression){
+      zkHost = factory.getCollectionZkHost(collectionName);
+      if(zkHost == null) {
+        zkHost = factory.getDefaultZkHost();
+      }
+    } else if(zkHostExpression.getParameter() instanceof StreamExpressionValue) {
+      zkHost = ((StreamExpressionValue)zkHostExpression.getParameter()).getValue();
+    }
+
+    if(null == zkHost){
+      throw new IOException(String.format(Locale.ROOT,"invalid expression %s - zkHost not found for collection '%s'",expression,collectionName));
+    }
+
+    // We've got all the required items
+    init(zkHost,
+         collectionName,
+         stream,
+         traverseFrom,
+         traverseTo ,
+         gather,
+         params,
+         metrics,
+         trackTraversal,
+         scatter);
+  }
+
+  private void init(String zkHost,
+                    String collection,
+                    TupleStream tupleStream,
+                    String traverseFrom,
+                    String traverseTo,
+                    String gather,
+                    Map queryParams,
+                    List<Metric> metrics,
+                    boolean trackTraversal,
+                    Set<Traversal.Scatter> scatter) {
+    this.zkHost = zkHost;
+    this.collection = collection;
+    this.tupleStream = tupleStream;
+    this.traverseFrom = traverseFrom;
+    this.traverseTo = traverseTo;
+    this.gather = gather;
+    this.queryParams = queryParams;
+    this.metrics = metrics;
+    this.trackTraversal = trackTraversal;
+    this.scatter = scatter;
+  }
+
+  @Override
+  public StreamExpressionParameter toExpression(StreamFactory factory) throws IOException {
+
+    StreamExpression expression = new StreamExpression(factory.getFunctionName(this.getClass()));
+
+    // collection
+    expression.addParameter(collection);
+
+    if(tupleStream instanceof Expressible){
+      expression.addParameter(((Expressible)tupleStream).toExpression(factory));
+    }
+    else{
+      throw new IOException("This GatherNodesStream contains a non-expressible TupleStream - it cannot be converted to an expression");
+    }
+
+    Set<Map.Entry> entries =  queryParams.entrySet();
+    // parameters
+    for(Map.Entry param : entries){
+      String value = param.getValue().toString();
+
+      // SOLR-8409: This is a special case where the params contain a " character
+      // Do note that in any other BASE streams with parameters where a " might come into play
+      // that this same replacement needs to take place.
+      value = value.replace("\"", "\\\"");
+
+      expression.addParameter(new StreamExpressionNamedParameter(param.getKey().toString(), value));
+    }
+
+    if(metrics != null) {
+      for (Metric metric : metrics) {
+        expression.addParameter(metric.toExpression(factory));
+      }
+    }
+
+    expression.addParameter(new StreamExpressionNamedParameter("zkHost", zkHost));
+    expression.addParameter(new StreamExpressionNamedParameter("gather", zkHost));
+    expression.addParameter(new StreamExpressionNamedParameter("walk", traverseFrom+"->"+traverseTo));
+    expression.addParameter(new StreamExpressionNamedParameter("trackTraversal", Boolean.toString(trackTraversal)));
+
+    StringBuilder buf = new StringBuilder();
+    for(Traversal.Scatter sc : scatter) {
+      if(buf.length() > 0 ) {
+        buf.append(",");
+      }
+      buf.append(sc.toString());
+    }
+
+    expression.addParameter(new StreamExpressionNamedParameter("scatter", buf.toString()));
+
+    return expression;
+  }
+
+  public void setStreamContext(StreamContext context) {
+    this.traversal = (Traversal) context.get("traversal");
+    if (traversal == null) {
+      //No traversal in the context. So create a new context and a new traversal.
+      //This ensures that two separate traversals in the same expression don't pollute each others traversal.
+      StreamContext localContext = new StreamContext();
+
+      localContext.numWorkers = context.numWorkers;
+      localContext.workerID = context.workerID;
+      localContext.setSolrClientCache(context.getSolrClientCache());
+      localContext.setStreamFactory(context.getStreamFactory());
+
+      for(Object key :context.getEntries().keySet()) {
+        localContext.put(key, context.get(key));
+      }
+
+      traversal = new Traversal();
+
+      localContext.put("traversal", traversal);
+
+      this.tupleStream.setStreamContext(localContext);
+      this.streamContext = localContext;
+    } else {
+      this.tupleStream.setStreamContext(context);
+      this.streamContext = context;
+    }
+  }
+
+  public List<TupleStream> children() {
+    List<TupleStream> l =  new ArrayList();
+    l.add(tupleStream);
+    return l;
+  }
+
+  public void open() throws IOException {
+    tupleStream.open();
+  }
+
+  private class JoinRunner implements Callable<List<Tuple>> {
+
+    private List<String> nodes;
+    private List<Tuple> edges = new ArrayList();
+
+    public JoinRunner(List<String> nodes) {
+      this.nodes = nodes;
+    }
+
+    public List<Tuple> call() {
+
+      Map joinParams = new HashMap();
+      Set<String> flSet = new HashSet();
+      flSet.add(gather);
+      flSet.add(traverseTo);
+
+      //Add the metric columns
+
+      if(metrics != null) {
+        for(Metric metric : metrics) {
+          for(String column : metric.getColumns()) {
+            flSet.add(column);
+          }
+        }
+      }
+
+      if(queryParams.containsKey("fl")) {
+        String flString = (String)queryParams.get("fl");
+        String[] flArray = flString.split(",");
+        for(String f : flArray) {
+          flSet.add(f.trim());
+        }
+      }
+
+      Iterator<String> it = flSet.iterator();
+      StringBuilder buf = new StringBuilder();
+      while(it.hasNext()) {
+        buf.append(it.next());
+        if(it.hasNext()) {
+          buf.append(",");
+        }
+      }
+
+      joinParams.putAll(queryParams);
+      joinParams.put("fl", buf.toString());
+      joinParams.put("qt", "/export");
+      joinParams.put("sort", gather + " asc,"+traverseTo +" asc");
+
+      StringBuffer nodeQuery = new StringBuffer();
+
+      for(String node : nodes) {
+        nodeQuery.append(node).append(" ");
+      }
+
+      String q = traverseTo + ":(" + nodeQuery.toString().trim() + ")";
+
+
+      joinParams.put("q", q);
+      TupleStream stream = null;
+      try {
+        stream = new UniqueStream(new CloudSolrStream(zkHost, collection, joinParams), new MultipleFieldEqualitor(new FieldEqualitor(gather), new FieldEqualitor(traverseTo)));
+        stream.setStreamContext(streamContext);
+        stream.open();
+        BATCH:
+        while (true) {
+          Tuple tuple = stream.read();
+          if (tuple.EOF) {
+            break BATCH;
+          }
+
+          edges.add(tuple);
+        }
+      } catch (Exception e) {
+        throw new RuntimeException(e);
+      } finally {
+        try {
+          stream.close();
+        } catch(Exception ce) {
+          throw new RuntimeException(ce);
+        }
+      }
+      return edges;
+    }
+  }
+
+
+  public void close() throws IOException {
+    tupleStream.close();
+  }
+
+  public Tuple read() throws IOException {
+
+    if (out == null) {
+      List<String> joinBatch = new ArrayList();
+      List<Future<List<Tuple>>> futures = new ArrayList();
+      Map<String, Node> level = new HashMap();
+
+      ExecutorService threadPool = null;
+      try {
+        threadPool = ExecutorUtil.newMDCAwareFixedThreadPool(4, new SolrjNamedThreadFactory("GatherNodesStream"));
+
+        Map<String, Node> roots = new HashMap();
+
+        while (true) {
+          Tuple tuple = tupleStream.read();
+          if (tuple.EOF) {
+            if (joinBatch.size() > 0) {
+              JoinRunner joinRunner = new JoinRunner(joinBatch);
+              Future future = threadPool.submit(joinRunner);
+              futures.add(future);
+            }
+            break;
+          }
+
+          String value = tuple.getString(traverseFrom);
+
+          if(traversal.getDepth() == 0) {
+            //This gathers the root nodes
+            //We check to see if there are dupes in the root nodes because root streams may not have been uniqued.
+            String key = collection+"."+value;
+            if(!roots.containsKey(key)) {
+              Node node = new Node(value, trackTraversal);
+              if (metrics != null) {
+                List<Metric> _metrics = new ArrayList();
+                for (Metric metric : metrics) {
+                  _metrics.add(metric.newInstance());
+                }
+                node.setMetrics(_metrics);
+              }
+
+              roots.put(key, node);
+            } else {
+              continue;
+            }
+          }
+
+          joinBatch.add(value);
+          if (joinBatch.size() == 400) {
+            JoinRunner joinRunner = new JoinRunner(joinBatch);
+            Future future = threadPool.submit(joinRunner);
+            futures.add(future);
+            joinBatch = new ArrayList();
+          }
+        }
+
+        if(traversal.getDepth() == 0) {
+          traversal.addLevel(roots, collection, traverseFrom);
+        }
+
+        this.traversal.setScatter(scatter);
+
+        if(useDefaultTraversal) {
+          this.trackTraversal = traversal.getTrackTraversal();
+        } else {
+          this.traversal.setTrackTraversal(trackTraversal);
+        }
+
+        for (Future<List<Tuple>> future : futures) {
+          List<Tuple> tuples = future.get();
+          for (Tuple tuple : tuples) {
+            String _traverseTo = tuple.getString(traverseTo);
+            String _gather = tuple.getString(gather);
+            String key = collection + "." + _gather;
+            if (!traversal.visited(key, _traverseTo, tuple)) {
+              Node node = level.get(key);
+              if (node != null) {
+                node.add((traversal.getDepth()-1)+"^"+_traverseTo, tuple);
+              } else {
+                node = new Node(_gather, trackTraversal);
+                if (metrics != null) {
+                  List<Metric> _metrics = new ArrayList();
+                  for (Metric metric : metrics) {
+                    _metrics.add(metric.newInstance());
+                  }
+                  node.setMetrics(_metrics);
+                }
+                node.add((traversal.getDepth()-1)+"^"+_traverseTo, tuple);
+                level.put(key, node);
+              }
+            }
+          }
+        }
+
+        traversal.addLevel(level, collection, gather);
+        out = traversal.iterator();
+      } catch(Exception e) {
+        throw new RuntimeException(e);
+      } finally {
+        threadPool.shutdown();
+      }
+    }
+
+    if (out.hasNext()) {
+      return out.next();
+    } else {
+      Map map = new HashMap();
+      map.put("EOF", true);
+      Tuple tuple = new Tuple(map);
+      return tuple;
+    }
+  }
+
+  public int getCost() {
+    return 0;
+  }
+
+  @Override
+  public StreamComparator getStreamSort() {
+    return null;
+  }
+
+  class NodeStream extends TupleStream {
+
+    private List<String> ids;
+    private Iterator<String> it;
+
+    public NodeStream(List<String> ids) {
+      this.ids = ids;
+    }
+
+    public void open() {this.it = ids.iterator();}
+    public void close() {}
+    public StreamComparator getStreamSort() {return null;}
+    public List<TupleStream> children() {return new ArrayList();}
+    public void setStreamContext(StreamContext context) {}
+
+    public Tuple read() {
+      HashMap map = new HashMap();
+      if(it.hasNext()) {
+        map.put("node",it.next());
+        return new Tuple(map);
+      } else {
+
+        map.put("EOF", true);
+        return new Tuple(map);
+      }
+    }
+  }
+}

solr/solrj/src/java/org/apache/solr/client/solrj/io/graph/Node.java

@@ -0,0 +1,90 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.client.solrj.io.graph;
+
+import org.apache.solr.client.solrj.io.Tuple;
+import org.apache.solr.client.solrj.io.stream.metrics.*;
+import java.util.*;
+
+public class Node {
+
+  private String id;
+  private List<Metric> metrics;
+  private Set<String> ancestors;
+
+  public Node(String id, boolean track) {
+    this.id=id;
+    if(track) {
+      ancestors = new HashSet();
+    }
+  }
+
+  public void setMetrics(List<Metric> metrics) {
+    this.metrics = metrics;
+  }
+
+  public void add(String ancestor, Tuple tuple) {
+    if(ancestors != null) {
+      ancestors.add(ancestor);
+    }
+
+    if(metrics != null) {
+      for(Metric metric : metrics) {
+        metric.update(tuple);
+      }
+    }
+  }
+
+  public Tuple toTuple(String collection, String field, int level, Traversal traversal) {
+    Map map = new HashMap();
+
+    map.put("node", id);
+    map.put("collection", collection);
+    map.put("field", field);
+    map.put("level", level);
+
+    boolean prependCollection = traversal.isMultiCollection();
+    List<String> cols = traversal.getCollections();
+
+    if(ancestors != null) {
+      List<String> l = new ArrayList();
+      for(String ancestor : ancestors) {
+        String[] ancestorParts = ancestor.split("\\^");
+
+        if(prependCollection) {
+          //prepend the collection
+          int colIndex = Integer.parseInt(ancestorParts[0]);
+          l.add(cols.get(colIndex)+"/"+ancestorParts[1]);
+        } else {
+          // Use only the ancestor id.
+          l.add(ancestorParts[1]);
+        }
+      }
+
+      map.put("ancestors", l);
+    }
+
+    if(metrics != null) {
+      for(Metric metric : metrics) {
+        map.put(metric.getIdentifier(), metric.getValue());
+      }
+    }
+
+    return new Tuple(map);
+  }
+}

solr/solrj/src/java/org/apache/solr/client/solrj/io/graph/Traversal.java

@@ -0,0 +1,96 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.client.solrj.io.graph;
+
+import org.apache.solr.client.solrj.io.Tuple;
+import java.util.*;
+
+public class Traversal {
+
+  private List<Map<String, Node>> graph = new ArrayList();
+  private List<String> fields = new ArrayList();
+  private List<String> collections = new ArrayList();
+  private Set<Scatter> scatter = new HashSet();
+  private Set<String> collectionSet = new HashSet();
+  private boolean trackTraversal;
+  private int depth;
+
+  public void addLevel(Map<String, Node> level, String collection, String field) {
+    graph.add(level);
+    collections.add(collection);
+    collectionSet.add(collection);
+    fields.add(field);
+    ++depth;
+  }
+
+  public int getDepth() {
+    return depth;
+  }
+
+  public boolean getTrackTraversal() {
+    return this.trackTraversal;
+  }
+
+  public boolean visited(String nodeId, String ancestorId, Tuple tuple) {
+    for(Map<String, Node> level : graph) {
+      Node node = level.get(nodeId);
+      if(node != null) {
+        node.add(depth+"^"+ancestorId, tuple);
+        return true;
+      }
+    }
+    return false;
+  }
+
+  public boolean isMultiCollection() {
+    return collectionSet.size() > 1;
+  }
+
+  public List<Map<String, Node>> getGraph() {
+    return graph;
+  }
+
+  public void setScatter(Set<Scatter> scatter) {
+    this.scatter = scatter;
+  }
+
+  public Set<Scatter> getScatter() {
+    return this.scatter;
+  }
+
+  public void setTrackTraversal(boolean trackTraversal) {
+    this.trackTraversal = trackTraversal;
+  }
+
+  public List<String> getCollections() {
+    return this.collections;
+  }
+
+  public List<String> getFields() {
+    return this.fields;
+  }
+
+  public enum Scatter {
+    BRANCHES,
+    LEAVES;
+  }
+
+  public Iterator<Tuple> iterator() {
+    return new TraversalIterator(this, scatter);
+  }
+}

solr/solrj/src/java/org/apache/solr/client/solrj/io/graph/TraversalIterator.java

@@ -0,0 +1,120 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.client.solrj.io.graph;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import org.apache.solr.client.solrj.io.Tuple;
+import org.apache.solr.client.solrj.io.graph.Traversal.Scatter;
+
+class TraversalIterator implements Iterator {
+
+  private List<Map<String,Node>> graph;
+  private List<String> collections;
+  private List<String> fields;
+
+  private Iterator<Iterator<Node>> graphIterator;
+  private Iterator<Node> levelIterator;
+
+  private Iterator<String> fieldIterator;
+  private Iterator<String> collectionIterator;
+  private Iterator<Integer> levelNumIterator;
+  private String outField;
+  private String outCollection;
+  private int outLevel;
+  private Traversal traversal;
+
+  public TraversalIterator(Traversal traversal, Set<Scatter> scatter) {
+    this.traversal = traversal;
+    graph = traversal.getGraph();
+    collections = traversal.getCollections();
+    fields = traversal.getFields();
+
+    List<String> outCollections = new ArrayList();
+    List<String> outFields = new ArrayList();
+    List<Integer> levelNums = new ArrayList();
+    List<Iterator<Node>> levelIterators = new ArrayList();
+
+    if(scatter.contains(Scatter.BRANCHES)) {
+      if(graph.size() > 1) {
+        for(int i=0; i<graph.size()-1; i++) {
+          Map<String, Node> graphLevel = graph.get(i);
+          String collection = collections.get(i);
+          String field = fields.get(i);
+          outCollections.add(collection);
+          outFields.add(field);
+          levelNums.add(i);
+          levelIterators.add(graphLevel.values().iterator());
+        }
+      }
+    }
+
+    if(scatter.contains(Scatter.LEAVES)) {
+      int leavesLevel = graph.size() > 1 ? graph.size()-1 : 0 ;
+      Map<String, Node> graphLevel = graph.get(leavesLevel);
+      String collection = collections.get(leavesLevel);
+      String field = fields.get(leavesLevel);
+      levelNums.add(leavesLevel);
+      outCollections.add(collection);
+      outFields.add(field);
+      levelIterators.add(graphLevel.values().iterator());
+    }
+
+    graphIterator = levelIterators.iterator();
+    levelIterator = graphIterator.next();
+
+    fieldIterator = outFields.iterator();
+    collectionIterator = outCollections.iterator();
+    levelNumIterator = levelNums.iterator();
+
+    outField = fieldIterator.next();
+    outCollection = collectionIterator.next();
+    outLevel = levelNumIterator.next();
+  }
+
+  @Override
+  public boolean hasNext() {
+    if(levelIterator.hasNext()) {
+      return true;
+    } else {
+      if(graphIterator.hasNext()) {
+        levelIterator = graphIterator.next();
+        outField = fieldIterator.next();
+        outCollection = collectionIterator.next();
+        outLevel = levelNumIterator.next();
+        return hasNext();
+      } else {
+        return false;
+      }
+    }
+  }
+
+  @Override
+  public Tuple next() {
+    if(hasNext()) {
+      Node node = levelIterator.next();
+      return node.toTuple(outCollection, outField, outLevel, traversal);
+    } else {
+     return null;
+    }
+  }
+}

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/StreamContext.java

@@ -49,6 +49,10 @@ public class StreamContext implements Serializable{
     this.entries.put(key, value);
   }
 
+  public Map getEntries() {
+    return this.entries;
+  }
+
   public void setSolrClientCache(SolrClientCache clientCache) {
     this.clientCache = clientCache;
   }

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/CountMetric.java

@@ -50,6 +50,10 @@ public class CountMetric extends Metric implements Serializable {
     
   }
 
+  public String[] getColumns() {
+    return new String[0];
+  }
+  
   private void init(String functionName){
     setFunctionName(functionName);
     setIdentifier(functionName, "(*)");

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/MaxMetric.java

@@ -67,6 +67,11 @@ public class MaxMetric extends Metric implements Serializable {
     }
   }
 
+  public String[] getColumns() {
+    String[] cols =  {columnName};
+    return cols;
+  }
+
   public void update(Tuple tuple) {
     Object o = tuple.get(columnName);
     if(o instanceof Double) {

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/MeanMetric.java

@@ -80,6 +80,11 @@ public class MeanMetric extends Metric implements Serializable {
     return new MeanMetric(columnName);
   }
 
+  public String[] getColumns() {
+    String[] cols =  {columnName};
+    return cols;
+  }
+
   public double getValue() {
     double dcount = (double)count;
     if(longSum == 0) {

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/Metric.java

@@ -54,4 +54,6 @@ public abstract class Metric implements Serializable, Expressible {
   public abstract double getValue();
   public abstract void update(Tuple tuple);
   public abstract Metric newInstance();
+  public abstract String[] getColumns();
+
 }

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/MinMetric.java

@@ -58,6 +58,11 @@ public class MinMetric extends Metric {
   }
 
 
+  public String[] getColumns() {
+    String[] cols =  {columnName};
+    return cols;
+  }
+
   public double getValue() {
     if(longMin == Long.MAX_VALUE) {
       return doubleMin;

solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/SumMetric.java

@@ -58,6 +58,11 @@ public class SumMetric extends Metric implements Serializable {
     setIdentifier(functionName, "(", columnName, ")");
   }
 
+  public String[] getColumns() {
+    String[] cols =  {columnName};
+    return cols;
+  }
+
   public void update(Tuple tuple) {
     Object o = tuple.get(columnName);
     if(o instanceof Double) {

solr/solrj/src/test/org/apache/solr/client/solrj/io/graph/GraphExpressionTest.java

@@ -20,6 +20,7 @@ package org.apache.solr.client.solrj.io.graph;
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -31,8 +32,15 @@ import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.LuceneTestCase.Slow;
 import org.apache.solr.client.solrj.io.SolrClientCache;
 import org.apache.solr.client.solrj.io.Tuple;
+import org.apache.solr.client.solrj.io.comp.ComparatorOrder;
+import org.apache.solr.client.solrj.io.comp.FieldComparator;
 import org.apache.solr.client.solrj.io.stream.*;
 import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+import org.apache.solr.client.solrj.io.stream.metrics.CountMetric;
+import org.apache.solr.client.solrj.io.stream.metrics.MaxMetric;
+import org.apache.solr.client.solrj.io.stream.metrics.MeanMetric;
+import org.apache.solr.client.solrj.io.stream.metrics.MinMetric;
+import org.apache.solr.client.solrj.io.stream.metrics.SumMetric;
 import org.apache.solr.cloud.AbstractFullDistribZkTestBase;
 import org.apache.solr.cloud.AbstractZkTestCase;
 import org.apache.solr.common.SolrInputDocument;
@@ -117,6 +125,8 @@ public class GraphExpressionTest extends AbstractFullDistribZkTestBase {
     commit();
 
     testShortestPathStream();
+    testGatherNodesStream();
+    testGatherNodesFriendsStream();
   }
 
   private void testShortestPathStream() throws Exception {
@@ -265,9 +275,399 @@ public class GraphExpressionTest extends AbstractFullDistribZkTestBase {
     commit();
   }
 
+
+  private void testGatherNodesStream() throws Exception {
+
+    indexr(id, "0", "basket_s", "basket1", "product_s", "product1", "price_f", "20");
+    indexr(id, "1", "basket_s", "basket1", "product_s", "product3", "price_f", "30");
+    indexr(id, "2", "basket_s", "basket1", "product_s", "product5", "price_f", "1");
+    indexr(id, "3", "basket_s", "basket2", "product_s", "product1", "price_f", "2");
+    indexr(id, "4", "basket_s", "basket2", "product_s", "product6", "price_f", "5");
+    indexr(id, "5", "basket_s", "basket2", "product_s", "product7", "price_f", "10");
+    indexr(id, "6", "basket_s", "basket3", "product_s", "product4", "price_f", "20");
+    indexr(id, "7", "basket_s", "basket3", "product_s", "product3", "price_f", "10");
+    indexr(id, "8", "basket_s", "basket3", "product_s", "product1", "price_f", "10");
+    indexr(id, "9", "basket_s", "basket4", "product_s", "product4", "price_f", "40");
+    indexr(id, "10", "basket_s", "basket4", "product_s", "product3", "price_f", "10");
+    indexr(id, "11", "basket_s", "basket4", "product_s", "product1", "price_f", "10");
+
+    commit();
+
+    List<Tuple> tuples = null;
+    Set<String> paths = null;
+    GatherNodesStream stream = null;
+    StreamContext context = new StreamContext();
+    SolrClientCache cache = new SolrClientCache();
+    context.setSolrClientCache(cache);
+
+    StreamFactory factory = new StreamFactory()
+        .withCollectionZkHost("collection1", zkServer.getZkAddress())
+        .withFunctionName("gatherNodes", GatherNodesStream.class)
+        .withFunctionName("search", CloudSolrStream.class)
+        .withFunctionName("count", CountMetric.class)
+        .withFunctionName("avg", MeanMetric.class)
+        .withFunctionName("sum", SumMetric.class)
+        .withFunctionName("min", MinMetric.class)
+        .withFunctionName("max", MaxMetric.class);
+
+    String expr = "gatherNodes(collection1, " +
+                               "walk=\"product1->product_s\"," +
+                               "gather=\"basket_s\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 4);
+    assertTrue(tuples.get(0).getString("node").equals("basket1"));
+    assertTrue(tuples.get(1).getString("node").equals("basket2"));
+    assertTrue(tuples.get(2).getString("node").equals("basket3"));
+    assertTrue(tuples.get(3).getString("node").equals("basket4"));
+
+    String expr2 = "gatherNodes(collection1, " +
+                                 expr+","+
+                                "walk=\"node->basket_s\"," +
+                                "gather=\"product_s\", count(*), avg(price_f), sum(price_f), min(price_f), max(price_f))";
+
+    stream = (GatherNodesStream)factory.constructStream(expr2);
+
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+
+    stream.setStreamContext(context);
+
+
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+
+
+    assertTrue(tuples.size() == 5);
+
+
+    assertTrue(tuples.get(0).getString("node").equals("product3"));
+    assertTrue(tuples.get(0).getDouble("count(*)").equals(3.0D));
+
+    assertTrue(tuples.get(1).getString("node").equals("product4"));
+    assertTrue(tuples.get(1).getDouble("count(*)").equals(2.0D));
+    assertTrue(tuples.get(1).getDouble("avg(price_f)").equals(30.0D));
+    assertTrue(tuples.get(1).getDouble("sum(price_f)").equals(60.0D));
+    assertTrue(tuples.get(1).getDouble("min(price_f)").equals(20.0D));
+    assertTrue(tuples.get(1).getDouble("max(price_f)").equals(40.0D));
+
+    assertTrue(tuples.get(2).getString("node").equals("product5"));
+    assertTrue(tuples.get(2).getDouble("count(*)").equals(1.0D));
+    assertTrue(tuples.get(3).getString("node").equals("product6"));
+    assertTrue(tuples.get(3).getDouble("count(*)").equals(1.0D));
+    assertTrue(tuples.get(4).getString("node").equals("product7"));
+    assertTrue(tuples.get(4).getDouble("count(*)").equals(1.0D));
+
+    //Test list of root nodes
+    expr = "gatherNodes(collection1, " +
+           "walk=\"product4, product7->product_s\"," +
+           "gather=\"basket_s\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+    tuples = getTuples(stream);
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 3);
+    assertTrue(tuples.get(0).getString("node").equals("basket2"));
+    assertTrue(tuples.get(1).getString("node").equals("basket3"));
+    assertTrue(tuples.get(2).getString("node").equals("basket4"));
+
+    //Test with negative filter query
+
+    expr = "gatherNodes(collection1, " +
+                        "walk=\"product4, product7->product_s\"," +
+                        "gather=\"basket_s\", fq=\"-basket_s:basket4\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 2);
+    assertTrue(tuples.get(0).getString("node").equals("basket2"));
+    assertTrue(tuples.get(1).getString("node").equals("basket3"));
+
+    cache.close();
+    del("*:*");
+    commit();
+  }
+
+  private void testGatherNodesFriendsStream() throws Exception {
+
+    indexr(id, "0", "from_s", "bill", "to_s", "jim", "message_t", "Hello jim");
+    indexr(id, "1", "from_s", "bill", "to_s", "sam", "message_t", "Hello sam");
+    indexr(id, "2", "from_s", "bill", "to_s", "max", "message_t", "Hello max");
+    indexr(id, "3", "from_s", "max",  "to_s", "kip", "message_t", "Hello kip");
+    indexr(id, "4", "from_s", "sam",  "to_s", "steve", "message_t", "Hello steve");
+    indexr(id, "5", "from_s", "jim",  "to_s", "ann", "message_t", "Hello steve");
+
+    commit();
+
+    List<Tuple> tuples = null;
+    Set<String> paths = null;
+    GatherNodesStream stream = null;
+    StreamContext context = new StreamContext();
+    SolrClientCache cache = new SolrClientCache();
+    context.setSolrClientCache(cache);
+
+    StreamFactory factory = new StreamFactory()
+        .withCollectionZkHost("collection1", zkServer.getZkAddress())
+        .withFunctionName("gatherNodes", GatherNodesStream.class)
+        .withFunctionName("search", CloudSolrStream.class)
+        .withFunctionName("count", CountMetric.class)
+        .withFunctionName("hashJoin", HashJoinStream.class)
+        .withFunctionName("avg", MeanMetric.class)
+        .withFunctionName("sum", SumMetric.class)
+        .withFunctionName("min", MinMetric.class)
+        .withFunctionName("max", MaxMetric.class);
+
+    String expr = "gatherNodes(collection1, " +
+                               "walk=\"bill->from_s\"," +
+                               "gather=\"to_s\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 3);
+    assertTrue(tuples.get(0).getString("node").equals("jim"));
+    assertTrue(tuples.get(1).getString("node").equals("max"));
+    assertTrue(tuples.get(2).getString("node").equals("sam"));
+
+    //Test scatter branches, leaves and trackTraversal
+
+    expr = "gatherNodes(collection1, " +
+           "walk=\"bill->from_s\"," +
+           "gather=\"to_s\","+
+           "scatter=\"branches, leaves\", trackTraversal=\"true\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 4);
+    assertTrue(tuples.get(0).getString("node").equals("bill"));
+    assertTrue(tuples.get(0).getLong("level").equals(new Long(0)));
+    assertTrue(tuples.get(0).getStrings("ancestors").size() == 0);
+    assertTrue(tuples.get(1).getString("node").equals("jim"));
+    assertTrue(tuples.get(1).getLong("level").equals(new Long(1)));
+    List<String> ancestors = tuples.get(1).getStrings("ancestors");
+    System.out.println("##################### Ancestors:"+ancestors);
+    assert(ancestors.size() == 1);
+    assert(ancestors.get(0).equals("bill"));
+
+    assertTrue(tuples.get(2).getString("node").equals("max"));
+    assertTrue(tuples.get(2).getLong("level").equals(new Long(1)));
+    ancestors = tuples.get(2).getStrings("ancestors");
+    assert(ancestors.size() == 1);
+    assert(ancestors.get(0).equals("bill"));
+
+    assertTrue(tuples.get(3).getString("node").equals("sam"));
+    assertTrue(tuples.get(3).getLong("level").equals(new Long(1)));
+    ancestors = tuples.get(3).getStrings("ancestors");
+    assert(ancestors.size() == 1);
+    assert(ancestors.get(0).equals("bill"));
+
+    // Test query root
+
+    expr = "gatherNodes(collection1, " +
+           "search(collection1, q=\"message_t:jim\", fl=\"from_s\", sort=\"from_s asc\"),"+
+           "walk=\"from_s->from_s\"," +
+           "gather=\"to_s\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 3);
+    assertTrue(tuples.get(0).getString("node").equals("jim"));
+    assertTrue(tuples.get(1).getString("node").equals("max"));
+    assertTrue(tuples.get(2).getString("node").equals("sam"));
+
+
+    // Test query root scatter branches
+
+    expr = "gatherNodes(collection1, " +
+           "search(collection1, q=\"message_t:jim\", fl=\"from_s\", sort=\"from_s asc\"),"+
+           "walk=\"from_s->from_s\"," +
+           "gather=\"to_s\", scatter=\"branches, leaves\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+    assertTrue(tuples.size() == 4);
+    assertTrue(tuples.get(0).getString("node").equals("bill"));
+    assertTrue(tuples.get(0).getLong("level").equals(new Long(0)));
+    assertTrue(tuples.get(1).getString("node").equals("jim"));
+    assertTrue(tuples.get(1).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(2).getString("node").equals("max"));
+    assertTrue(tuples.get(2).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(3).getString("node").equals("sam"));
+    assertTrue(tuples.get(3).getLong("level").equals(new Long(1)));
+
+    expr = "gatherNodes(collection1, " +
+           "search(collection1, q=\"message_t:jim\", fl=\"from_s\", sort=\"from_s asc\"),"+
+           "walk=\"from_s->from_s\"," +
+           "gather=\"to_s\")";
+
+    String expr2 = "gatherNodes(collection1, " +
+                    expr+","+
+                   "walk=\"node->from_s\"," +
+                   "gather=\"to_s\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr2);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+
+    assertTrue(tuples.size() == 3);
+    assertTrue(tuples.get(0).getString("node").equals("ann"));
+    assertTrue(tuples.get(1).getString("node").equals("kip"));
+    assertTrue(tuples.get(2).getString("node").equals("steve"));
+
+
+    //Test two traversals in the same expression
+    String expr3 = "hashJoin("+expr2+", hashed="+expr2+", on=\"node\")";
+
+    HashJoinStream hstream = (HashJoinStream)factory.constructStream(expr3);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    hstream.setStreamContext(context);
+
+    tuples = getTuples(hstream);
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+
+    assertTrue(tuples.size() == 3);
+    assertTrue(tuples.get(0).getString("node").equals("ann"));
+    assertTrue(tuples.get(1).getString("node").equals("kip"));
+    assertTrue(tuples.get(2).getString("node").equals("steve"));
+
+    //=================================
+
+
+    expr = "gatherNodes(collection1, " +
+           "search(collection1, q=\"message_t:jim\", fl=\"from_s\", sort=\"from_s asc\"),"+
+           "walk=\"from_s->from_s\"," +
+           "gather=\"to_s\")";
+
+    expr2 = "gatherNodes(collection1, " +
+            expr+","+
+            "walk=\"node->from_s\"," +
+            "gather=\"to_s\", scatter=\"branches, leaves\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr2);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+
+
+    assertTrue(tuples.size() == 7);
+    assertTrue(tuples.get(0).getString("node").equals("ann"));
+    assertTrue(tuples.get(0).getLong("level").equals(new Long(2)));
+    assertTrue(tuples.get(1).getString("node").equals("bill"));
+    assertTrue(tuples.get(1).getLong("level").equals(new Long(0)));
+    assertTrue(tuples.get(2).getString("node").equals("jim"));
+    assertTrue(tuples.get(2).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(3).getString("node").equals("kip"));
+    assertTrue(tuples.get(3).getLong("level").equals(new Long(2)));
+    assertTrue(tuples.get(4).getString("node").equals("max"));
+    assertTrue(tuples.get(4).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(5).getString("node").equals("sam"));
+    assertTrue(tuples.get(5).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(6).getString("node").equals("steve"));
+    assertTrue(tuples.get(6).getLong("level").equals(new Long(2)));
+
+    //Add a cycle from jim to bill
+    indexr(id, "6", "from_s", "jim", "to_s", "bill", "message_t", "Hello steve");
+    indexr(id, "7", "from_s", "sam", "to_s", "bill", "message_t", "Hello steve");
+
+    commit();
+
+    expr = "gatherNodes(collection1, " +
+           "search(collection1, q=\"message_t:jim\", fl=\"from_s\", sort=\"from_s asc\"),"+
+           "walk=\"from_s->from_s\"," +
+           "gather=\"to_s\", trackTraversal=\"true\")";
+
+    expr2 = "gatherNodes(collection1, " +
+             expr+","+
+            "walk=\"node->from_s\"," +
+            "gather=\"to_s\", scatter=\"branches, leaves\", trackTraversal=\"true\")";
+
+    stream = (GatherNodesStream)factory.constructStream(expr2);
+    context = new StreamContext();
+    context.setSolrClientCache(cache);
+    stream.setStreamContext(context);
+
+    tuples = getTuples(stream);
+    Collections.sort(tuples, new FieldComparator("node", ComparatorOrder.ASCENDING));
+
+    assertTrue(tuples.size() == 7);
+    assertTrue(tuples.get(0).getString("node").equals("ann"));
+    assertTrue(tuples.get(0).getLong("level").equals(new Long(2)));
+    //Bill should now have one ancestor
+    assertTrue(tuples.get(1).getString("node").equals("bill"));
+    assertTrue(tuples.get(1).getLong("level").equals(new Long(0)));
+    assertTrue(tuples.get(1).getStrings("ancestors").size() == 2);
+    List<String> anc = tuples.get(1).getStrings("ancestors");
+
+    Collections.sort(anc);
+    assertTrue(anc.get(0).equals("jim"));
+    assertTrue(anc.get(1).equals("sam"));
+
+    assertTrue(tuples.get(2).getString("node").equals("jim"));
+    assertTrue(tuples.get(2).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(3).getString("node").equals("kip"));
+    assertTrue(tuples.get(3).getLong("level").equals(new Long(2)));
+    assertTrue(tuples.get(4).getString("node").equals("max"));
+    assertTrue(tuples.get(4).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(5).getString("node").equals("sam"));
+    assertTrue(tuples.get(5).getLong("level").equals(new Long(1)));
+    assertTrue(tuples.get(6).getString("node").equals("steve"));
+    assertTrue(tuples.get(6).getLong("level").equals(new Long(2)));
+
+    cache.close();
+    del("*:*");
+    commit();
+  }
+
+
+
   protected List<Tuple> getTuples(TupleStream tupleStream) throws IOException {
     tupleStream.open();
-    List<Tuple> tuples = new ArrayList<Tuple>();
+    List<Tuple> tuples = new ArrayList();
     for(Tuple t = tupleStream.read(); !t.EOF; t = tupleStream.read()) {
       tuples.add(t);
     }