Merge pull request #5639 from vespa-engine/balder/reduce-memory-footprint-for-rankprofiles

Balder/reduce memory footprint for rankprofiles

21 files changed, 99 insertions, 82 deletions

diff --git a/searchlib/src/main/java/com/yahoo/searchlib/expression/ExpressionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/expression/ExpressionNode.java
index f995f424f97..2e4519597ef 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/expression/ExpressionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/expression/ExpressionNode.java
@@ -13,7 +13,7 @@ import java.io.Serializable;
  * happens in the C++ backend. This class hierarchy is for <b>building</b> the expression tree to pass to the backend.
  *
  * @author baldersheim
- * @author <a href="mailto:simon@yahoo-inc.com">Simon Thoresen</a>
+ * @author Simon Thoresen
  */
 public abstract class ExpressionNode extends Identifiable implements Serializable {
 
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/ExpressionFunction.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/ExpressionFunction.java
index 262aba89f27..a3ab21a5966 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/ExpressionFunction.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/ExpressionFunction.java
@@ -55,10 +55,10 @@ public class ExpressionFunction {
      */
     public Instance expand(SerializationContext context, List<ExpressionNode> argumentValues, Deque<String> path) {
         Map<String, String> argumentBindings = new HashMap<>();
-        for (int i = 0; i < arguments.size() && i < arguments.size(); ++i) {
-            argumentBindings.put(arguments.get(i), argumentValues.get(i).toString(context, path, null));
+        for (int i = 0; i < arguments.size() && i < argumentValues.size(); ++i) {
+            argumentBindings.put(arguments.get(i), argumentValues.get(i).toString(new StringBuilder(), context, path, null).toString());
         }
-        return new Instance(toSymbol(argumentBindings), body.getRoot().toString(context.withBindings(argumentBindings), path, null));
+        return new Instance(toSymbol(argumentBindings), body.getRoot().toString(new StringBuilder(), context.withBindings(argumentBindings), path, null).toString());
     }
 
     /**
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/RankingExpression.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/RankingExpression.java
index 6b2422d7cb2..6fa5b1196fa 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/RankingExpression.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/RankingExpression.java
@@ -246,7 +246,7 @@ public class RankingExpression implements Serializable {
     public Map<String, String> getRankProperties(List<ExpressionFunction> macros) {
         Deque<String> path = new LinkedList<>();
         SerializationContext context = new SerializationContext(macros);
-        String serializedRoot = root.toString(context, path, null);
+        String serializedRoot = root.toString(new StringBuilder(), context, path, null).toString();
         Map<String, String> serializedExpressions = context.serializedFunctions();
         serializedExpressions.put(propertyName(name), serializedRoot);
         return serializedExpressions;
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/Reference.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/Reference.java
index 35974c39f69..c42d9ecc37f 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/Reference.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/Reference.java
@@ -21,7 +21,6 @@ import java.util.stream.Collectors;
  */
 public class Reference extends TypeContext.Name {
 
-    private final String name;
     private final Arguments arguments;
 
     /**
@@ -33,13 +32,10 @@ public class Reference extends TypeContext.Name {
         super(name);
         Objects.requireNonNull(name, "name cannot be null");
         Objects.requireNonNull(arguments, "arguments cannot be null");
-        this.name = name;
         this.arguments = arguments;
         this.output = output;
     }
 
-    public String name() { return name; }
-
     public Arguments arguments() { return arguments; }
 
     public String output() { return output; }
@@ -48,9 +44,7 @@ public class Reference extends TypeContext.Name {
      * Creates a reference to a simple feature consisting of a name and a single argument
      */
     public static Reference simple(String name, String argumentValue) {
-        return new Reference(name,
-                             new Arguments(new ReferenceNode(argumentValue)),
-                             null);
+        return new Reference(name, new Arguments(new ReferenceNode(argumentValue)), null);
     }
 
     /**
@@ -111,11 +105,11 @@ public class Reference extends TypeContext.Name {
     }
 
     public Reference withArguments(Arguments arguments) {
-        return new Reference(name, arguments, output);
+        return new Reference(name(), arguments, output);
     }
 
     public Reference withOutput(String output) {
-        return new Reference(name, arguments, output);
+        return new Reference(name(), arguments, output);
     }
 
     @Override
@@ -123,7 +117,7 @@ public class Reference extends TypeContext.Name {
         if (o == this) return true;
         if (!(o instanceof Reference)) return false;
         Reference other = (Reference) o;
-        if (!Objects.equals(other.name, this.name)) return false;
+        if (!Objects.equals(other.name(), this.name())) return false;
         if (!Objects.equals(other.arguments, this.arguments)) return false;
         if (!Objects.equals(other.output, this.output)) return false;
         return true;
@@ -131,23 +125,31 @@ public class Reference extends TypeContext.Name {
 
     @Override
     public int hashCode() {
-        return Objects.hash(name, arguments, output);
+        return Objects.hash(name(), arguments, output);
     }
 
     @Override
     public String toString() {
-        return toString(new SerializationContext(), null, null);
+        return toString(new StringBuilder(), new SerializationContext(), null, null).toString();
     }
 
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        StringBuilder b = new StringBuilder(name);
-        if (arguments != null && arguments.expressions().size() > 0)
-            b.append("(").append(arguments.expressions().stream()
-                                                        .map(node -> node.toString(context, path, parent))
-                                                        .collect(Collectors.joining(","))).append(")");
+    public StringBuilder toString(StringBuilder b, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        b.append(name());
+        if (arguments.expressions().size() > 0) {
+            b.append("(");
+            for (int i = 0; i < arguments.expressions().size(); i++) {
+                ExpressionNode e = arguments.expressions().get(i);
+                e.toString(b, context, path, parent);
+                if (i+1 < arguments.expressions().size()) {
+                    b.append(',');
+                }
+
+            }
+            b.append(")");
+        }
         if (output != null)
             b.append(".").append(output);
-        return b.toString();
+        return b;
     }
 
 }
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTForestNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTForestNode.java
index 649c70122f1..579162196dc 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTForestNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTForestNode.java
@@ -42,8 +42,8 @@ public class GBDTForestNode extends ExpressionNode {
     }
 
     /** Returns (optimized sum of condition trees) */
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return "(optimized sum of condition trees of size " + (values.length*8) + " bytes)";
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return string.append("(optimized sum of condition trees of size ").append(values.length*8).append(" bytes)");
     }
 
 }
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTNode.java
index 53a286f09f6..3c0898b5d4f 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTNode.java
@@ -98,7 +98,7 @@ public final class GBDTNode extends ExpressionNode {
 
     /** Returns "(optimized condition tree)" */
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return "(optimized condition tree)";
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return string.append("(optimized condition tree)");
     }
 }
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ArithmeticNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ArithmeticNode.java
index 49c49bed9bd..575b9b5b3fb 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ArithmeticNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ArithmeticNode.java
@@ -41,26 +41,23 @@ public final class ArithmeticNode extends CompositeNode {
     public List<ExpressionNode> children() { return children; }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        StringBuilder string = new StringBuilder();
-
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
         boolean nonDefaultPrecedence = nonDefaultPrecedence(parent);
         if (nonDefaultPrecedence)
             string.append("(");
 
         Iterator<ExpressionNode> child = children.iterator();
-        string.append(child.next().toString(context, path, this)).append(" ");
+        child.next().toString(string, context, path, this).append(" ");
         for (Iterator<ArithmeticOperator> op = operators.iterator(); op.hasNext() && child.hasNext();) {
             string.append(op.next().toString()).append(" ");
-            string.append(child.next().toString(context, path, this));
+            child.next().toString(string, context, path, this);
             if (op.hasNext())
                 string.append(" ");
         }
         if (nonDefaultPrecedence)
             string.append(")");
-        string.append(" ");
 
-        return string.toString().trim();
+        return string;
     }
 
     /**
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ComparisonNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ComparisonNode.java
index eb328486045..c4ecea22f7e 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ComparisonNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ComparisonNode.java
@@ -44,9 +44,9 @@ public class ComparisonNode extends BooleanNode {
     public ExpressionNode getRightCondition() { return rightCondition; }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return leftCondition.toString(context, path, this) + " " + operator + " " +
-               rightCondition.toString(context, path, this);
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        leftCondition.toString(string, context, path, this).append(' ').append(operator).append(' ');
+        return rightCondition.toString(string, context, path, this);
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ConstantNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ConstantNode.java
index 3ddd7223349..64ad4d1ffce 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ConstantNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ConstantNode.java
@@ -39,8 +39,8 @@ public final class ConstantNode extends ExpressionNode {
     public Value getValue() { return value; }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return sourceString();
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return string.append(sourceString());
     }
 
     /** Returns the string which created this, or the value.toString() if not known */
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/EmbracedNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/EmbracedNode.java
index 47c2897e4a4..4844ad82b27 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/EmbracedNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/EmbracedNode.java
@@ -39,10 +39,10 @@ public final class EmbracedNode extends CompositeNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        String expression = value.toString(context, path, this);
-        if (value instanceof ReferenceNode)  return expression;
-        return  "(" + expression + ")";
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        if (value instanceof ReferenceNode)
+            return value.toString(string, context, path, this);
+        return value.toString(string.append('('), context, path, this).append(')');
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ExpressionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ExpressionNode.java
index 6bb163590de..a02108a8bda 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ExpressionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ExpressionNode.java
@@ -30,18 +30,33 @@ public abstract class ExpressionNode implements Serializable {
 
     @Override
     public final String toString() {
-        return toString(new SerializationContext(), null, null);
+        return toString(new StringBuilder(), new SerializationContext(), null, null).toString();
     }
 
     /**
      * Returns a script instance of this based on the supplied script functions.
      *
+     * @param builder the StringBuilder that will be appended to
      * @param context the serialization context
      * @param path the call path to this, used for cycle detection, or null if this is a root
      * @param parent the parent node of this, or null if it a root
      * @return the main script, referring to script instances.
      */
-    public abstract String toString(SerializationContext context, Deque<String> path, CompositeNode parent);
+    public abstract StringBuilder toString(StringBuilder builder, SerializationContext context, Deque<String> path, CompositeNode parent);
+
+    /**
+     * Returns a script instance of this based on the supplied script functions.
+     * @deprecated use the faster one that takes and returns a StringBuilder instead.
+     *
+     * @param context the serialization context
+     * @param path the call path to this, used for cycle detection, or null if this is a root
+     * @param parent the parent node of this, or null if it a root
+     * @return the main script, referring to script instances.
+     */
+    @Deprecated
+    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return toString(new StringBuilder(), context, path, parent).toString();
+    }
 
     /**
      * Returns the type this will return if evaluated with the given context.
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/FunctionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/FunctionNode.java
index 1da2210a39c..07efd46e02c 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/FunctionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/FunctionNode.java
@@ -54,17 +54,15 @@ public final class FunctionNode extends CompositeNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        StringBuilder b=new StringBuilder(function.toString());
-        b.append("(");
+    public StringBuilder toString(StringBuilder b, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        b.append(function.toString()).append("(");
         for (int i = 0; i < this.arguments.expressions().size(); ++i) {
-            b.append(this.arguments.expressions().get(i).toString(context, path, this));
+            this.arguments.expressions().get(i).toString(b, context, path, this);
             if (i < this.arguments.expressions().size() - 1) {
                 b.append(",");
             }
         }
-        b.append(")");
-        return b.toString();
+        return b.append(")");
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/GeneratorLambdaFunctionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/GeneratorLambdaFunctionNode.java
index c87eb0ace39..886e179b838 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/GeneratorLambdaFunctionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/GeneratorLambdaFunctionNode.java
@@ -44,8 +44,8 @@ public class GeneratorLambdaFunctionNode extends CompositeNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return generator.toString(context, path, this);
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return generator.toString(string, context, path, this);
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/IfNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/IfNode.java
index ee4edac4941..06b899d45ab 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/IfNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/IfNode.java
@@ -67,12 +67,15 @@ public final class IfNode extends CompositeNode {
     public Double getTrueProbability() { return trueProbability; }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return "if (" +
-               condition.toString(context, path, this) + ", " +
-               trueExpression.toString(context, path, this) + ", " +
-               falseExpression.toString(context, path, this) +
-                (trueProbability != null ? ", " + trueProbability : "") + ")";
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        string.append("if (");
+        condition.toString(string, context, path, this).append(", ");
+        trueExpression.toString(string, context, path, this).append(", ");
+        falseExpression.toString(string, context, path, this);
+        if (trueProbability != null) {
+            string.append(", ").append(trueProbability);
+        }
+        return string.append(')');
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/LambdaFunctionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/LambdaFunctionNode.java
index 61086f8182a..de98b01287e 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/LambdaFunctionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/LambdaFunctionNode.java
@@ -44,8 +44,9 @@ public class LambdaFunctionNode extends CompositeNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return ("f(" + commaSeparated(arguments) + ")(" + functionExpression.toString(context, path, this)) + ")";
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        string.append("f(").append(commaSeparated(arguments)).append(")(");
+        return functionExpression.toString(string, context, path, this).append(")");
     }
 
     private String commaSeparated(List<String> list) {
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NameNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NameNode.java
index f1adf331630..6fc1091c557 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NameNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NameNode.java
@@ -29,8 +29,8 @@ public final class NameNode extends ExpressionNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return name;
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return string.append(name);
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NegativeNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NegativeNode.java
index fcc03dc4862..a71034e022b 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NegativeNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NegativeNode.java
@@ -34,8 +34,8 @@ public class NegativeNode extends CompositeNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return "-" + value.toString(context, path, parent);
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        return value.toString(string.append('-'), context, path, parent);
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NotNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NotNode.java
index a539f496ff5..0a75ba78df6 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NotNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/NotNode.java
@@ -34,8 +34,9 @@ public class NotNode extends BooleanNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        return "!" + value.toString(context, path, parent);
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        string.append("!");
+        return value.toString(string, context, path, parent);
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ReferenceNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ReferenceNode.java
index 639c5d22d9e..e2dc170c168 100755
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ReferenceNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ReferenceNode.java
@@ -63,11 +63,11 @@ public final class ReferenceNode extends CompositeNode {
     public List<ExpressionNode> children() { return reference.arguments().expressions(); }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
         // A reference to a macro argument?
         if (reference.isIdentifier() && context.getBinding(getName()) != null) {
             // a bound identifier: replace by the value it is bound to
-            return context.getBinding(getName());
+            return string.append(context.getBinding(getName()));
         }
 
         // A reference to a function?
@@ -83,11 +83,11 @@ public final class ReferenceNode extends CompositeNode {
             ExpressionFunction.Instance instance = function.expand(context, getArguments().expressions(), path);
             path.removeLast();
             context.addFunctionSerialization(RankingExpression.propertyName(instance.getName()), instance.getExpressionString());
-            return "rankingExpression(" + instance.getName() + ")";
+            return string.append("rankingExpression(").append(instance.getName()).append(')');
         }
 
         // Not resolved in this context: output as-is
-        return reference.toString(context, path, parent);
+        return reference.toString(string, context, path, parent);
     }
 
     /** Returns the reference of this node */
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/SetMembershipNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/SetMembershipNode.java
index cb31219579a..9b3bd674814 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/SetMembershipNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/SetMembershipNode.java
@@ -47,17 +47,17 @@ public class SetMembershipNode extends BooleanNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
-        StringBuilder b = new StringBuilder(testValue.toString(context, path, this));
-        b.append(" in [");
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
+        testValue.toString(string, context, path, this);
+        string.append(" in [");
         for (int i = 0, len = setValues.size(); i < len; ++i) {
-            b.append(setValues.get(i).toString(context, path, this));
+            setValues.get(i).toString(string, context, path, this);
             if (i < len - 1) {
-                b.append(", ");
+                string.append(", ");
             }
         }
-        b.append("]");
-        return b.toString();
+        string.append("]");
+        return string;
     }
 
     @Override
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java
index 6c9b6bb4a98..c1732aabf0b 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java
@@ -59,9 +59,9 @@ public class TensorFunctionNode extends CompositeNode {
     }
 
     @Override
-    public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
+    public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
         // Serialize as primitive
-        return function.toPrimitive().toString(new ExpressionNodeToStringContext(context, path, this));
+        return string.append(function.toPrimitive().toString(new ExpressionNodeToStringContext(context, path, this)));
     }
 
     @Override
@@ -131,7 +131,7 @@ public class TensorFunctionNode extends CompositeNode {
         public String toString(ToStringContext c) {
             if (c instanceof ExpressionNodeToStringContext) {
                 ExpressionNodeToStringContext context = (ExpressionNodeToStringContext) c;
-                return expression.toString(context.context, context.path, context.parent);
+                return expression.toString(new StringBuilder(),context.context, context.path, context.parent).toString();
             }
             else {
                 return expression.toString();