diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
index 2ad14c8..29a89bc 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
@@ -117,6 +117,8 @@
 
 	private final AtomicReference<AlternateHandle[]> alternates;
 
+	private final UnpackedObjectCache unpackedObjectCache;
+
 	/**
 	 * Initialize a reference to an on-disk object directory.
 	 *
@@ -140,6 +142,7 @@
 		packDirectory = new File(objects, "pack");
 		alternatesFile = new File(infoDirectory, "alternates");
 		packList = new AtomicReference<PackList>(NO_PACKS);
+		unpackedObjectCache = new UnpackedObjectCache();
 		this.fs = fs;
 
 		alternates = new AtomicReference<AlternateHandle[]>();
@@ -179,6 +182,8 @@
 
 	@Override
 	public void close() {
+		unpackedObjectCache.clear();
+
 		final PackList packs = packList.get();
 		packList.set(NO_PACKS);
 		for (final PackFile p : packs.packs)
@@ -255,6 +260,8 @@
 	}
 
 	boolean hasObject1(final AnyObjectId objectId) {
+		if (unpackedObjectCache.isUnpacked(objectId))
+			return true;
 		for (final PackFile p : packList.get().packs) {
 			try {
 				if (p.hasObject(objectId)) {
@@ -328,6 +335,14 @@
 
 	ObjectLoader openObject1(final WindowCursor curs,
 			final AnyObjectId objectId) throws IOException {
+		if (unpackedObjectCache.isUnpacked(objectId)) {
+			ObjectLoader ldr = openObject2(curs, objectId.name(), objectId);
+			if (ldr != null)
+				return ldr;
+			else
+				unpackedObjectCache.remove(objectId);
+		}
+
 		PackList pList = packList.get();
 		SEARCH: for (;;) {
 			for (final PackFile p : pList.packs) {
@@ -429,15 +444,21 @@
 			File path = fileFor(objectName);
 			FileInputStream in = new FileInputStream(path);
 			try {
+				unpackedObjectCache.add(objectId);
 				return UnpackedObject.open(in, path, objectId, curs);
 			} finally {
 				in.close();
 			}
 		} catch (FileNotFoundException noFile) {
+			unpackedObjectCache.remove(objectId);
 			return null;
 		}
 	}
 
+	void addUnpackedObject(ObjectId id) {
+		unpackedObjectCache.add(id);
+	}
+
 	boolean tryAgain1() {
 		final PackList old = packList.get();
 		if (old.tryAgain(packDirectory.lastModified()))
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectoryInserter.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectoryInserter.java
index 5016679..a1f224c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectoryInserter.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectoryInserter.java
@@ -91,16 +91,20 @@
 		}
 
 		final File dst = db.fileFor(id);
-		if (tmp.renameTo(dst))
+		if (tmp.renameTo(dst)) {
+			db.addUnpackedObject(id);
 			return id;
+		}
 
 		// Maybe the directory doesn't exist yet as the object
 		// directories are always lazily created. Note that we
 		// try the rename first as the directory likely does exist.
 		//
 		dst.getParentFile().mkdir();
-		if (tmp.renameTo(dst))
+		if (tmp.renameTo(dst)) {
+			db.addUnpackedObject(id);
 			return id;
+		}
 
 		if (db.has(id)) {
 			tmp.delete();
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObjectCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObjectCache.java
new file mode 100644
index 0000000..4d05c6f
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObjectCache.java
@@ -0,0 +1,149 @@
+/*
+ * Copyright (C) 2010, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.storage.file;
+
+import java.util.concurrent.atomic.AtomicReferenceArray;
+
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.ObjectId;
+
+/** Remembers objects that are currently unpacked. */
+class UnpackedObjectCache {
+	private static final int INITIAL_BITS = 5; // size = 32
+
+	private static final int MAX_BITS = 11; // size = 2048
+
+	private volatile Table table;
+
+	UnpackedObjectCache() {
+		table = new Table(INITIAL_BITS);
+	}
+
+	boolean isUnpacked(AnyObjectId objectId) {
+		return table.contains(objectId);
+	}
+
+	void add(AnyObjectId objectId) {
+		Table t = table;
+		if (t.add(objectId)) {
+			// The object either already exists in the table, or was
+			// successfully added. Either way leave the table alone.
+			//
+		} else {
+			// The object won't fit into the table. Implement a crude
+			// cache removal by just dropping the table away, but double
+			// it in size for the next incarnation.
+			//
+			Table n = new Table(Math.min(t.bits + 1, MAX_BITS));
+			n.add(objectId);
+			table = n;
+		}
+	}
+
+	void remove(AnyObjectId objectId) {
+		if (isUnpacked(objectId))
+			clear();
+	}
+
+	void clear() {
+		table = new Table(INITIAL_BITS);
+	}
+
+	private static class Table {
+		private static final int MAX_CHAIN = 8;
+
+		private final AtomicReferenceArray<ObjectId> ids;
+
+		private final int shift;
+
+		final int bits;
+
+		Table(int bits) {
+			this.ids = new AtomicReferenceArray<ObjectId>(1 << bits);
+			this.shift = 32 - bits;
+			this.bits = bits;
+		}
+
+		boolean contains(AnyObjectId toFind) {
+			int i = index(toFind);
+			for (int n = 0; n < MAX_CHAIN; n++) {
+				ObjectId obj = ids.get(i);
+				if (obj == null)
+					break;
+
+				if (AnyObjectId.equals(obj, toFind))
+					return true;
+
+				if (++i == ids.length())
+					i = 0;
+			}
+			return false;
+		}
+
+		boolean add(AnyObjectId toAdd) {
+			int i = index(toAdd);
+			for (int n = 0; n < MAX_CHAIN;) {
+				ObjectId obj = ids.get(i);
+				if (obj == null) {
+					if (ids.compareAndSet(i, null, toAdd.copy()))
+						return true;
+					else
+						continue;
+				}
+
+				if (AnyObjectId.equals(obj, toAdd))
+					return true;
+
+				if (++i == ids.length())
+					i = 0;
+				n++;
+			}
+			return false;
+		}
+
+		private int index(AnyObjectId id) {
+			return id.hashCode() >>> shift;
+		}
+	}
+}