--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/tmatesoft/hg/internal/IntVector.java	Sat Sep 10 00:18:39 2011 +0200
@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2011 TMate Software Ltd
+ *  
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * For information on how to redistribute this software under
+ * the terms of a license other than GNU General Public License
+ * contact TMate Software at support@hg4j.com
+ */
+package org.tmatesoft.hg.internal;
+
+/**
+ *
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+class IntVector {
+	
+	private int[] data;
+	private final int increment;
+	private int count;
+
+
+	public IntVector() {
+		this(16, -1);
+	}
+
+	// increment == -1: grow by power of two.
+	// increment == 0: no resize (Exception will be thrown on attempt to add past capacity)
+	public IntVector(int initialCapacity, int increment) {
+		data = new int[initialCapacity];
+		this.increment = increment; 
+	}
+
+	public void add(int v) {
+		if (count == data.length) {
+			grow();
+		}
+		data[count++] = v;
+	}
+	
+	public int get(int i) {
+		if (i < 0 || i >= count) {
+			throw new IndexOutOfBoundsException(String.format("Index: %d, size: %d", i, count));
+		}
+		return data[i];
+	}
+	
+	public int size() {
+		return count;
+	}
+
+	public int[] toArray() {
+		int[] rv = new int[count];
+		System.arraycopy(data, 0, rv, 0, count);
+		return rv;
+	}
+
+	/**
+	 * Use only when this instance won't be used any longer
+	 */
+	@Experimental
+	int[] toArray(boolean internalIfSizeMatchCapacity) {
+		if (count == data.length) {
+			return data;
+		}
+		return toArray();
+	}
+
+	private void grow() {
+		if (increment == 0) {
+			// throw specific exception right away
+			return;
+		}
+		int newCapacity = increment < 0 ? data.length << 1 : data.length + increment;
+		assert newCapacity > 0 && newCapacity != data.length : newCapacity;
+		int[] newData = new int[newCapacity];
+		System.arraycopy(data, 0, newData, 0, count);
+		data = newData;
+	}
+}

--- a/src/org/tmatesoft/hg/internal/RevlogStream.java	Wed Sep 07 09:33:27 2011 +0200
+++ b/src/org/tmatesoft/hg/internal/RevlogStream.java	Sat Sep 10 00:18:39 2011 +0200
@@ -269,8 +269,6 @@
 		if (baseRevisions != null && baseRevisions.length > 0) {
 			return;
 		}
-		ArrayList<Integer> resBases = new ArrayList<Integer>();
-		ArrayList<Integer> resOffsets = new ArrayList<Integer>();
 		DataAccess da = getIndexStream();
 		try {
 			if (da.isEmpty()) {
@@ -282,6 +280,14 @@
 			da.readInt(); // just to skip next 4 bytes of offset + flags
 			final int INLINEDATA = 1 << 16;
 			inline = (versionField & INLINEDATA) != 0;
+			IntVector resBases, resOffsets = null;
+			int entryCountGuess = da.length() / REVLOGV1_RECORD_SIZE;
+			if (inline) {
+				entryCountGuess >>>= 2; // pure guess, assume useful data takes 3/4 of total space
+				resOffsets = new IntVector(entryCountGuess, 5000);
+			}
+			resBases = new IntVector(entryCountGuess, 5000);
+			
 			long offset = 0; // first offset is always 0, thus Hg uses it for other purposes
 			while(true) {
 				int compressedLen = da.readInt();
@@ -309,9 +315,9 @@
 				}
 				if (da.isEmpty()) {
 					// fine, done then
-					baseRevisions = toArray(resBases);
+					baseRevisions = resBases.toArray(true);
 					if (inline) {
-						indexRecordOffset = toArray(resOffsets);
+						indexRecordOffset = resOffsets.toArray(true);
 					}
 					break;
 				} else {