diff --git a/java/src/main/java/org/softwareheritage/graph/maps/LabelMapBuilder.java b/java/src/main/java/org/softwareheritage/graph/maps/LabelMapBuilder.java
index 27019fa..db8fbfd 100644
--- a/java/src/main/java/org/softwareheritage/graph/maps/LabelMapBuilder.java
+++ b/java/src/main/java/org/softwareheritage/graph/maps/LabelMapBuilder.java
@@ -1,307 +1,373 @@
 package org.softwareheritage.graph.maps;
 
 import com.martiansoftware.jsap.*;
 import it.unimi.dsi.big.webgraph.LazyLongIterator;
 import it.unimi.dsi.big.webgraph.labelling.ArcLabelledImmutableGraph;
 import it.unimi.dsi.big.webgraph.labelling.BitStreamArcLabelledImmutableGraph;
 import it.unimi.dsi.fastutil.BigArrays;
 import it.unimi.dsi.fastutil.Size64;
 import it.unimi.dsi.fastutil.bytes.ByteArrays;
 import it.unimi.dsi.fastutil.io.BinIO;
 import it.unimi.dsi.fastutil.io.FastBufferedInputStream;
 import it.unimi.dsi.fastutil.longs.LongBigArrays;
+import it.unimi.dsi.fastutil.longs.LongIterator;
 import it.unimi.dsi.fastutil.objects.Object2LongFunction;
 import it.unimi.dsi.io.OutputBitStream;
 import it.unimi.dsi.logging.ProgressLogger;
 import it.unimi.dsi.big.webgraph.BVGraph;
 import it.unimi.dsi.big.webgraph.ImmutableGraph;
 import it.unimi.dsi.big.webgraph.NodeIterator;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.softwareheritage.graph.labels.DirEntry;
 import org.softwareheritage.graph.labels.SwhLabel;
 
 import java.io.*;
 import java.lang.reflect.Array;
 import java.nio.charset.StandardCharsets;
 import java.util.*;
 import java.util.concurrent.TimeUnit;
 
 public class LabelMapBuilder {
     final static String SORT_BUFFER_SIZE = "40%";
     final static Logger logger = LoggerFactory.getLogger(LabelMapBuilder.class);
 
     String graphPath;
     String debugPath;
     String tmpDir;
     ImmutableGraph graph;
 
     Object2LongFunction<byte[]> swhIdMph;
     long[][] orderMap;
     Object2LongFunction<byte[]> filenameMph;
     long numFilenames;
     int totalLabelWidth;
 
     public LabelMapBuilder(String graphPath, String debugPath, String tmpDir) {
         this.graphPath = graphPath;
         this.debugPath = debugPath;
         this.tmpDir = tmpDir;
     }
 
     private static JSAPResult parse_args(String[] args) {
         JSAPResult config = null;
         try {
             SimpleJSAP jsap = new SimpleJSAP(LabelMapBuilder.class.getName(), "",
                     new Parameter[]{
                             new FlaggedOption("graphPath", JSAP.STRING_PARSER, JSAP.NO_DEFAULT, JSAP.REQUIRED, 'g',
                                     "graph", "Basename of the compressed graph"),
                             new FlaggedOption("debugPath", JSAP.STRING_PARSER, JSAP.NO_DEFAULT, JSAP.NOT_REQUIRED, 'd',
                                     "debug-path", "Store the intermediate representation here for debug"),
 
                             new FlaggedOption("tmpDir", JSAP.STRING_PARSER, "tmp", JSAP.NOT_REQUIRED, 't', "tmp",
                                     "Temporary directory path"),});
 
             config = jsap.parse(args);
             if (jsap.messagePrinted()) {
                 System.exit(1);
             }
         } catch (JSAPException e) {
             e.printStackTrace();
         }
         return config;
     }
 
     public static void main(String[] args) throws IOException {
         JSAPResult config = parse_args(args);
         String graphPath = config.getString("graphPath");
         String tmpDir = config.getString("tmpDir");
         String debugPath = config.getString("debugPath");
 
         LabelMapBuilder builder = new LabelMapBuilder(graphPath, debugPath, tmpDir);
+
+        logger.info("Loading graph and MPH functions...");
+        builder.loadGraph();
+
         builder.computeLabelMap();
     }
 
     @SuppressWarnings("unchecked") // Suppress warning for Object2LongFunction cast
     static Object2LongFunction<byte[]> loadMPH(String mphBasename) throws IOException {
         Object2LongFunction<byte[]> mphMap = null;
         try {
             mphMap = (Object2LongFunction<byte[]>) BinIO.loadObject(mphBasename + ".mph");
         } catch (ClassNotFoundException e) {
             logger.error("unknown class object in .mph file: " + e);
             System.exit(2);
         }
         return mphMap;
     }
 
     static long getMPHSize(Object2LongFunction<byte[]> mph) {
         return (mph instanceof Size64) ? ((Size64) mph).size64() : mph.size();
     }
 
     void computeLabelMap() throws IOException {
         /*
          * Pass the intermediate representation to sort(1) so that we see the labels in the order they will
          * appear in the label file.
          */
-        logger.info("Loading graph and MPH functions...");
-        loadGraph();
-
-        logger.info("Hashing the input labels...");
-
         ProcessBuilder processBuilder = new ProcessBuilder();
         processBuilder.command("sort", "-k1,1n", "-k2,2n", // Numerical sort
                 "--numeric-sort", "--buffer-size", SORT_BUFFER_SIZE, "--temporary-directory", tmpDir);
         Process sort = processBuilder.start();
         BufferedOutputStream sort_stdin = new BufferedOutputStream(sort.getOutputStream());
         BufferedInputStream sort_stdout = new BufferedInputStream(sort.getInputStream());
 
         final FastBufferedInputStream fbis = new FastBufferedInputStream(System.in);
         hashLabelStream(fbis, sort_stdin);
         sort_stdin.close();
 
-        logger.info("Writing label map to file...");
-        writeLabels(sort_stdout);
+        EdgeLabelLineIterator mapLines = new TextualEdgeLabelLineIterator(sort_stdout);
+        writeLabels(mapLines);
 
         logger.info("Done");
     }
 
     void loadGraph() throws IOException {
         graph = BVGraph.loadMapped(graphPath);
 
         swhIdMph = loadMPH(graphPath);
 
         orderMap = LongBigArrays.newBigArray(getMPHSize(swhIdMph));
         BinIO.loadLongs(graphPath + ".order", orderMap);
 
         filenameMph = loadMPH(graphPath + "-labels");
         numFilenames = getMPHSize(filenameMph);
         totalLabelWidth = DirEntry.labelWidth(numFilenames);
     }
 
     void hashLabelStream(FastBufferedInputStream input, BufferedOutputStream output) throws IOException {
         // Compute intermediate representation and write it on :
         // "<src node id> <dst node id> <label ids>\n"
         ProgressLogger plInter = new ProgressLogger(logger, 10, TimeUnit.SECONDS);
         plInter.itemsName = "edges";
         plInter.expectedUpdates = graph.numArcs();
         plInter.start("Hashing the label stream");
 
         var charset = StandardCharsets.US_ASCII;
         byte[] array = new byte[1024];
         for (long line = 0;; line++) {
             int start = 0, len;
             while ((len = input.readLine(array, start, array.length - start,
                     FastBufferedInputStream.ALL_TERMINATORS)) == array.length - start) {
                 start += len;
                 array = ByteArrays.grow(array, array.length + 1);
             }
             if (len == -1)
                 break; // EOF
             final int lineLength = start + len;
 
             // Skip whitespace at the start of the line.
             int offset = 0;
             while (offset < lineLength && array[offset] >= 0 && array[offset] <= ' ')
                 offset++;
             if (offset == lineLength) {
                 continue;
             }
             if (array[0] == '#')
                 continue;
 
             // Scan source id.
             start = offset;
             while (offset < lineLength && (array[offset] < 0 || array[offset] > ' '))
                 offset++;
             final byte[] ss = Arrays.copyOfRange(array, start, offset);
 
             // Skip whitespace between identifiers.
             while (offset < lineLength && array[offset] >= 0 && array[offset] <= ' ')
                 offset++;
             if (offset == lineLength) {
                 logger.error("Error at line " + line + ": no target");
                 continue;
             }
 
             // Scan target ID
             start = offset;
             while (offset < lineLength && (array[offset] < 0 || array[offset] > ' '))
                 offset++;
             final byte[] ts = Arrays.copyOfRange(array, start, offset);
 
             // Skip whitespace between identifiers.
             while (offset < lineLength && array[offset] >= 0 && array[offset] <= ' ')
                 offset++;
             if (offset == lineLength)
                 continue; // No label, skip
 
             // Scan label
             start = offset;
             while (offset < lineLength && (array[offset] < 0 || array[offset] > ' '))
                 offset++;
             final byte[] ls = Arrays.copyOfRange(array, start, offset);
 
             // Skip whitespace between identifiers.
             while (offset < lineLength && array[offset] >= 0 && array[offset] <= ' ')
                 offset++;
             // Scan permission
             int permission = 0;
             if (offset < lineLength) {
                 start = offset;
                 while (offset < lineLength && (array[offset] < 0 || array[offset] > ' '))
                     offset++;
                 permission = Integer.parseInt(new String(array, start, offset - start, charset));
             }
 
             // System.err.format("DEBUG: read %s %s %s %d\n", ss, ts, ls, permission);
 
             long s = swhIdMph.getLong(ss);
             long t = swhIdMph.getLong(ts);
             long filenameId = filenameMph.getLong(ls);
 
             long srcNode = BigArrays.get(orderMap, s);
             long dstNode = BigArrays.get(orderMap, t);
 
             output.write((srcNode + "\t" + dstNode + "\t" + filenameId + "\t" + permission + "\n")
                     .getBytes(StandardCharsets.US_ASCII));
             plInter.lightUpdate();
         }
         plInter.done();
     }
 
-    void writeLabels(InputStream sortedMapping) throws IOException {
+    void writeLabels(EdgeLabelLineIterator mapLines) throws IOException {
         // Get the sorted output and write the labels and label offsets
         ProgressLogger plLabels = new ProgressLogger(logger, 10, TimeUnit.SECONDS);
-        plLabels.itemsName = "nodes";
-        plLabels.expectedUpdates = graph.numNodes();
+        plLabels.itemsName = "edges";
+        plLabels.expectedUpdates = graph.numArcs();
+        plLabels.start("Hashing the label stream");
 
         FileWriter debugFile = null;
         if (debugPath != null) {
             debugFile = new FileWriter(debugPath);
         }
 
         OutputBitStream labels = new OutputBitStream(
                 new File(graphPath + "-labelled" + BitStreamArcLabelledImmutableGraph.LABELS_EXTENSION));
         OutputBitStream offsets = new OutputBitStream(
                 new File(graphPath + "-labelled" + BitStreamArcLabelledImmutableGraph.LABEL_OFFSETS_EXTENSION));
         offsets.writeGamma(0);
 
-        Scanner mapLines = new Scanner(sortedMapping, StandardCharsets.US_ASCII);
+        EdgeLabelLine line = new EdgeLabelLine(-1, -1, -1, -1);
 
         NodeIterator it = graph.nodeIterator();
-        long labelSrcNode = -1;
-        long labelDstNode = -1;
-        long labelFilenameId = -1;
-        int labelPermission = -1;
+        boolean started = false;
 
         ArrayList<DirEntry> labelBuffer = new ArrayList<>(128);
         while (it.hasNext()) {
             long srcNode = it.nextLong();
+            if (!started) {
+                plLabels.start("Writing label map to file...");
+                started = true;
+            }
 
             int bits = 0;
             LazyLongIterator s = it.successors();
             long dstNode;
             while ((dstNode = s.nextLong()) >= 0) {
-                while (labelSrcNode <= srcNode && labelDstNode <= dstNode) {
-                    if (labelSrcNode == srcNode && labelDstNode == dstNode) {
-                        labelBuffer.add(new DirEntry(labelFilenameId, labelPermission));
+                while (line.srcNode <= srcNode && line.dstNode <= dstNode) {
+                    if (line.srcNode == srcNode && line.dstNode == dstNode) {
+                        labelBuffer.add(new DirEntry(line.filenameId, line.permission));
 
                         if (debugFile != null) {
-                            debugFile.write(labelSrcNode + " " + labelDstNode + " " + labelFilenameId + " "
-                                    + labelPermission + "\n");
+                            debugFile.write(line.srcNode + " " + line.dstNode + " " + line.filenameId + " "
+                                    + line.permission + "\n");
                         }
                     }
 
                     if (!mapLines.hasNext())
                         break;
 
-                    String line = mapLines.nextLine();
-                    String[] parts = line.split("\\t");
-                    labelSrcNode = Long.parseLong(parts[0]);
-                    labelDstNode = Long.parseLong(parts[1]);
-                    labelFilenameId = Long.parseLong(parts[2]);
-                    labelPermission = Integer.parseInt(parts[3]);
+                    line = mapLines.next();
                 }
 
                 SwhLabel l = new SwhLabel("edgelabel", totalLabelWidth, labelBuffer.toArray(new DirEntry[0]));
                 labelBuffer.clear();
                 bits += l.toBitStream(labels, -1);
             }
             offsets.writeGamma(bits);
             plLabels.lightUpdate();
         }
 
         labels.close();
         offsets.close();
         plLabels.done();
         if (debugFile != null) {
             debugFile.close();
         }
 
         PrintWriter pw = new PrintWriter(new FileWriter((new File(graphPath)).getName() + "-labelled.properties"));
         pw.println(ImmutableGraph.GRAPHCLASS_PROPERTY_KEY + " = " + BitStreamArcLabelledImmutableGraph.class.getName());
         pw.println(BitStreamArcLabelledImmutableGraph.LABELSPEC_PROPERTY_KEY + " = " + SwhLabel.class.getName()
                 + "(DirEntry," + totalLabelWidth + ")");
         pw.println(ArcLabelledImmutableGraph.UNDERLYINGGRAPH_PROPERTY_KEY + " = " + graphPath);
         pw.close();
     }
+
+    public static class EdgeLabelLine {
+        public long srcNode;
+        public long dstNode;
+        public long filenameId;
+        public int permission;
+
+        public EdgeLabelLine(long labelSrcNode, long labelDstNode, long labelFilenameId, int labelPermission) {
+            this.srcNode = labelSrcNode;
+            this.dstNode = labelDstNode;
+            this.filenameId = labelFilenameId;
+            this.permission = labelPermission;
+        }
+    }
+
+    public abstract static class EdgeLabelLineIterator implements Iterator<EdgeLabelLine> {
+        @Override
+        public abstract boolean hasNext();
+        @Override
+        public abstract EdgeLabelLine next();
+    }
+
+    public static class TextualEdgeLabelLineIterator extends EdgeLabelLineIterator {
+        private final Scanner scanner;
+
+        public TextualEdgeLabelLineIterator(InputStream stream) {
+            scanner = new Scanner(stream, StandardCharsets.US_ASCII);
+        }
+
+        @Override
+        public boolean hasNext() {
+            return scanner.hasNext();
+        }
+        @Override
+        public EdgeLabelLine next() {
+            String line = scanner.nextLine();
+            String[] parts = line.split("\\t");
+            return new EdgeLabelLine(
+                Long.parseLong(parts[0]),
+                Long.parseLong(parts[1]),
+                Long.parseLong(parts[2]),
+                Integer.parseInt(parts[3])
+            );
+        }
+    }
+
+    public static class BinaryEdgeLabelLineIterator extends EdgeLabelLineIterator {
+        private final Scanner scanner;
+
+        public BinaryEdgeLabelLineIterator(InputStream stream) {
+            scanner = new Scanner(stream, StandardCharsets.US_ASCII);
+        }
+
+        @Override
+        public boolean hasNext() {
+            return scanner.hasNext();
+        }
+        @Override
+        public EdgeLabelLine next() {
+            String line = scanner.nextLine();
+            String[] parts = line.split("\\t");
+            return new EdgeLabelLine(
+                    Long.parseLong(parts[0]),
+                    Long.parseLong(parts[1]),
+                    Long.parseLong(parts[2]),
+                    Integer.parseInt(parts[3])
+            );
+        }
+    }
 }