Merge changes I1ca7acb4,Ia41b7a1c,I33b65286,Ie2823724,I6b65bfb4

* changes:
  DHT: Change DhtReadher caches to be dynamic by workload
  DHT: Use a proper HashMap for RecentChunk lookups
  DHT: Always have at least one recent chunk in DhtReader
  DHT: Fix NPE during prefetch
  DHT: Drop leading hash digits from row keys

11 files changed, 193 insertions, 92 deletions

diff --git a/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ChunkKeyTest.java b/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ChunkKeyTest.java
index 63cbf520c0..9219663667 100644
--- a/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ChunkKeyTest.java
+++ b/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ChunkKeyTest.java
@@ -43,7 +43,8 @@
 
 package org.eclipse.jgit.storage.dht;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 
 import org.eclipse.jgit.lib.ObjectId;
 import org.junit.Test;
@@ -59,19 +60,19 @@ public class ChunkKeyTest {
 		ChunkKey key1 = ChunkKey.create(repo1, id);
 		assertEquals(repo1.asInt(), key1.getRepositoryId());
 		assertEquals(id, key1.getChunkHash());
-		assertEquals("3e.41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
+		assertEquals("41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
 				key1.asString());
 
 		ChunkKey key2 = ChunkKey.fromBytes(key1.asBytes());
 		assertEquals(repo1.asInt(), key2.getRepositoryId());
 		assertEquals(id, key2.getChunkHash());
-		assertEquals("3e.41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
+		assertEquals("41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
 				key2.asString());
 
 		ChunkKey key3 = ChunkKey.fromString(key1.asString());
 		assertEquals(repo1.asInt(), key3.getRepositoryId());
 		assertEquals(id, key3.getChunkHash());
-		assertEquals("3e.41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
+		assertEquals("41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
 				key3.asString());
 
 		assertEquals(key1, key2);
diff --git a/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ObjectIndexKeyTest.java b/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ObjectIndexKeyTest.java
index ab3b423ede..d3419bd140 100644
--- a/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ObjectIndexKeyTest.java
+++ b/org.eclipse.jgit.storage.dht.test/tst/org/eclipse/jgit/storage/dht/ObjectIndexKeyTest.java
@@ -58,19 +58,19 @@ public class ObjectIndexKeyTest {
 		ObjectIndexKey key1 = ObjectIndexKey.create(repo, id);
 		assertEquals(repo.asInt(), key1.getRepositoryId());
 		assertEquals(key1, id);
-		assertEquals("3e.41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
+		assertEquals("41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
 				key1.asString());
 
 		ObjectIndexKey key2 = ObjectIndexKey.fromBytes(key1.asBytes());
 		assertEquals(repo.asInt(), key2.getRepositoryId());
 		assertEquals(key2, id);
-		assertEquals("3e.41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
+		assertEquals("41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
 				key2.asString());
 
 		ObjectIndexKey key3 = ObjectIndexKey.fromString(key1.asString());
 		assertEquals(repo.asInt(), key3.getRepositoryId());
 		assertEquals(key3, id);
-		assertEquals("3e.41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
+		assertEquals("41234567.3e64b928d51b3a28e89cfe2a3f0eeae35ef07839",
 				key3.asString());
 	}
 }
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ChunkKey.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ChunkKey.java
index 272b5ea173..11a151f6ba 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ChunkKey.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ChunkKey.java
@@ -54,7 +54,7 @@ import org.eclipse.jgit.lib.ObjectId;
 
 /** Unique identifier of a {@link PackChunk} in the DHT. */
 public final class ChunkKey implements RowKey {
-	static final int KEYLEN = 52;
+	static final int KEYLEN = 49;
 
 	/**
 	 * @param repo
@@ -84,8 +84,8 @@ public final class ChunkKey implements RowKey {
 			throw new IllegalArgumentException(MessageFormat.format(
 					DhtText.get().invalidChunkKey, decode(key, ptr, ptr + len)));
 
-		int repo = parse32(key, ptr + 3);
-		ObjectId chunk = ObjectId.fromString(key, ptr + 12);
+		int repo = parse32(key, ptr);
+		ObjectId chunk = ObjectId.fromString(key, ptr + 9);
 		return new ChunkKey(repo, chunk);
 	}
 
@@ -122,13 +122,9 @@ public final class ChunkKey implements RowKey {
 
 	public byte[] asBytes() {
 		byte[] r = new byte[KEYLEN];
-		chunk.copyTo(r, 12);
-		format32(r, 3, repo);
-		// bucket is the leading 2 digits of the SHA-1.
-		r[11] = '.';
-		r[2] = '.';
-		r[1] = r[12 + 1];
-		r[0] = r[12 + 0];
+		format32(r, 0, repo);
+		r[8] = '.';
+		chunk.copyTo(r, 9);
 		return r;
 	}
 
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtCachedPack.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtCachedPack.java
index 39a76463fb..0fd253bfbf 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtCachedPack.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtCachedPack.java
@@ -125,9 +125,18 @@ public class DhtCachedPack extends CachedPack {
 			throws IOException {
 		if (keyList == null)
 			init();
-		Prefetcher p = new Prefetcher(ctx, 0);
-		p.push(Arrays.asList(keyList));
-		copyPack(out, p, validate);
+
+		// Clear the recent chunks because all of the reader's
+		// chunk limit should be made available for prefetch.
+		int cacheLimit = ctx.getOptions().getChunkLimit();
+		ctx.getRecentChunks().setMaxBytes(0);
+		try {
+			Prefetcher p = new Prefetcher(ctx, 0, cacheLimit);
+			p.push(Arrays.asList(keyList));
+			copyPack(out, p, validate);
+		} finally {
+			ctx.getRecentChunks().setMaxBytes(cacheLimit);
+		}
 	}
 
 	private void copyPack(PackOutputStream out, Prefetcher prefetcher,
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReader.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReader.java
index f9288b9e2e..330b5c0734 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReader.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReader.java
@@ -156,6 +156,10 @@ public class DhtReader extends ObjectReader implements ObjectReuseAsIs {
 		return recentInfo;
 	}
 
+	RecentChunks getRecentChunks() {
+		return recentChunks;
+	}
+
 	DeltaBaseCache getDeltaBaseCache() {
 		return deltaBaseCache;
 	}
@@ -242,7 +246,7 @@ public class DhtReader extends ObjectReader implements ObjectReuseAsIs {
 		// configured as push might invoke our own methods that may
 		// try to call back into the active prefetcher.
 		//
-		Prefetcher p = new Prefetcher(this, OBJ_COMMIT);
+		Prefetcher p = prefetch(OBJ_COMMIT, readerOptions.getWalkCommitsPrefetchRatio());
 		p.push(this, roots);
 		prefetcher = p;
 	}
@@ -256,7 +260,7 @@ public class DhtReader extends ObjectReader implements ObjectReuseAsIs {
 		// configured as push might invoke our own methods that may
 		// try to call back into the active prefetcher.
 		//
-		Prefetcher p = new Prefetcher(this, OBJ_TREE);
+		Prefetcher p = prefetch(OBJ_TREE, readerOptions.getWalkTreesPrefetchRatio());
 		p.push(this, min.getTree(), max.getTree());
 		prefetcher = p;
 	}
@@ -391,14 +395,22 @@ public class DhtReader extends ObjectReader implements ObjectReuseAsIs {
 		new RepresentationSelector(packer, this, monitor).select(itr);
 	}
 
+	private Prefetcher prefetch(final int type, final int ratio) {
+		int limit = readerOptions.getChunkLimit();
+		int prefetchLimit = (int) (limit * (ratio / 100.0));
+		recentChunks.setMaxBytes(limit - prefetchLimit);
+		return new Prefetcher(this, type, prefetchLimit);
+	}
+
 	private void endPrefetch() {
+		recentChunks.setMaxBytes(getOptions().getChunkLimit());
 		prefetcher = null;
 	}
 
 	@SuppressWarnings("unchecked")
 	public void writeObjects(PackOutputStream out, List<ObjectToPack> objects)
 			throws IOException {
-		prefetcher = new Prefetcher(this, 0);
+		prefetcher = prefetch(0, readerOptions.getWriteObjectsPrefetchRatio());
 		try {
 			List itr = objects;
 			new ObjectWriter(this, prefetcher).plan(itr);
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReaderOptions.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReaderOptions.java
index 0890e39ad0..db3f51028f 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReaderOptions.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/DhtReaderOptions.java
@@ -57,7 +57,15 @@ public class DhtReaderOptions {
 
 	private boolean prefetchFollowEdgeHints;
 
-	private int prefetchLimit;
+	private int chunkLimit;
+
+	private int openQueuePrefetchRatio;
+
+	private int walkCommitsPrefetchRatio;
+
+	private int walkTreesPrefetchRatio;
+
+	private int writeObjectsPrefetchRatio;
 
 	private int objectIndexConcurrentBatches;
 
@@ -69,15 +77,18 @@ public class DhtReaderOptions {
 
 	private int recentInfoCacheSize;
 
-	private int recentChunkCacheSize;
-
 	private boolean trackFirstChunkLoad;
 
 	/** Create a default reader configuration. */
 	public DhtReaderOptions() {
 		setTimeout(Timeout.seconds(5));
 		setPrefetchFollowEdgeHints(true);
-		setPrefetchLimit(5 * MiB);
+
+		setChunkLimit(5 * MiB);
+		setOpenQueuePrefetchRatio(20 /* percent */);
+		setWalkCommitsPrefetchRatio(20 /* percent */);
+		setWalkTreesPrefetchRatio(20 /* percent */);
+		setWriteObjectsPrefetchRatio(90 /* percent */);
 
 		setObjectIndexConcurrentBatches(2);
 		setObjectIndexBatchSize(512);
@@ -86,7 +97,6 @@ public class DhtReaderOptions {
 		setDeltaBaseCacheLimit(10 * MiB);
 
 		setRecentInfoCacheSize(4096);
-		setRecentChunkCacheSize(4);
 	}
 
 	/** @return default timeout to wait on long operations before aborting. */
@@ -125,19 +135,83 @@ public class DhtReaderOptions {
 		return this;
 	}
 
-	/** @return number of bytes to load during prefetching. */
-	public int getPrefetchLimit() {
-		return prefetchLimit;
+	/** @return number of bytes to hold within a DhtReader. */
+	public int getChunkLimit() {
+		return chunkLimit;
 	}
 
 	/**
-	 * Set the number of bytes the prefetcher should hold onto.
+	 * Set the number of bytes hold within a DhtReader.
 	 *
 	 * @param maxBytes
 	 * @return {@code this}
 	 */
-	public DhtReaderOptions setPrefetchLimit(int maxBytes) {
-		prefetchLimit = Math.max(1024, maxBytes);
+	public DhtReaderOptions setChunkLimit(int maxBytes) {
+		chunkLimit = Math.max(1024, maxBytes);
+		return this;
+	}
+
+	/** @return percentage of {@link #getChunkLimit()} used for prefetch, 0..100. */
+	public int getOpenQueuePrefetchRatio() {
+		return openQueuePrefetchRatio;
+	}
+
+	/**
+	 * Set the prefetch ratio used by the open object queue.
+	 *
+	 * @param ratio 0..100.
+	 * @return {@code this}
+	 */
+	public DhtReaderOptions setOpenQueuePrefetchRatio(int ratio) {
+		openQueuePrefetchRatio = Math.max(0, Math.min(ratio, 100));
+		return this;
+	}
+
+	/** @return percentage of {@link #getChunkLimit()} used for prefetch, 0..100. */
+	public int getWalkCommitsPrefetchRatio() {
+		return walkCommitsPrefetchRatio;
+	}
+
+	/**
+	 * Set the prefetch ratio used by the open object queue.
+	 *
+	 * @param ratio 0..100.
+	 * @return {@code this}
+	 */
+	public DhtReaderOptions setWalkCommitsPrefetchRatio(int ratio) {
+		walkCommitsPrefetchRatio = Math.max(0, Math.min(ratio, 100));
+		return this;
+	}
+
+	/** @return percentage of {@link #getChunkLimit()} used for prefetch, 0..100. */
+	public int getWalkTreesPrefetchRatio() {
+		return walkTreesPrefetchRatio;
+	}
+
+	/**
+	 * Set the prefetch ratio used by the open object queue.
+	 *
+	 * @param ratio 0..100.
+	 * @return {@code this}
+	 */
+	public DhtReaderOptions setWalkTreesPrefetchRatio(int ratio) {
+		walkTreesPrefetchRatio = Math.max(0, Math.min(ratio, 100));
+		return this;
+	}
+
+	/** @return percentage of {@link #getChunkLimit()} used for prefetch, 0..100. */
+	public int getWriteObjectsPrefetchRatio() {
+		return writeObjectsPrefetchRatio;
+	}
+
+	/**
+	 * Set the prefetch ratio used by the open object queue.
+	 *
+	 * @param ratio 0..100.
+	 * @return {@code this}
+	 */
+	public DhtReaderOptions setWriteObjectsPrefetchRatio(int ratio) {
+		writeObjectsPrefetchRatio = Math.max(0, Math.min(ratio, 100));
 		return this;
 	}
 
@@ -226,24 +300,6 @@ public class DhtReaderOptions {
 		return this;
 	}
 
-	/** @return number of recent chunks to hold onto per-reader. */
-	public int getRecentChunkCacheSize() {
-		return recentChunkCacheSize;
-	}
-
-	/**
-	 * Set the number of chunks each reader holds onto for recently used access.
-	 *
-	 * @param chunkCnt
-	 *            the number of chunks each reader retains of recently used
-	 *            chunks to smooth out access.
-	 * @return {@code this}
-	 */
-	public DhtReaderOptions setRecentChunkCacheSize(int chunkCnt) {
-		recentChunkCacheSize = Math.max(0, chunkCnt);
-		return this;
-	}
-
 	/**
 	 * @return true if {@link DhtReader.Statistics} includes the stack trace for
 	 *         the first time a chunk is loaded. Supports debugging DHT code.
@@ -277,7 +333,11 @@ public class DhtReaderOptions {
 	public DhtReaderOptions fromConfig(Config rc) {
 		setTimeout(Timeout.getTimeout(rc, "core", "dht", "timeout", getTimeout()));
 		setPrefetchFollowEdgeHints(rc.getBoolean("core", "dht", "prefetchFollowEdgeHints", isPrefetchFollowEdgeHints()));
-		setPrefetchLimit(rc.getInt("core", "dht", "prefetchLimit", getPrefetchLimit()));
+		setChunkLimit(rc.getInt("core", "dht", "chunkLimit", getChunkLimit()));
+		setOpenQueuePrefetchRatio(rc.getInt("core", "dht", "openQueuePrefetchRatio", getOpenQueuePrefetchRatio()));
+		setWalkCommitsPrefetchRatio(rc.getInt("core", "dht", "walkCommitsPrefetchRatio", getWalkCommitsPrefetchRatio()));
+		setWalkTreesPrefetchRatio(rc.getInt("core", "dht", "walkTreesPrefetchRatio", getWalkTreesPrefetchRatio()));
+		setWriteObjectsPrefetchRatio(rc.getInt("core", "dht", "writeObjectsPrefetchRatio", getWriteObjectsPrefetchRatio()));
 
 		setObjectIndexConcurrentBatches(rc.getInt("core", "dht", "objectIndexConcurrentBatches", getObjectIndexConcurrentBatches()));
 		setObjectIndexBatchSize(rc.getInt("core", "dht", "objectIndexBatchSize", getObjectIndexBatchSize()));
@@ -286,7 +346,6 @@ public class DhtReaderOptions {
 		setDeltaBaseCacheLimit(rc.getInt("core", "dht", "deltaBaseCacheLimit", getDeltaBaseCacheLimit()));
 
 		setRecentInfoCacheSize(rc.getInt("core", "dht", "recentInfoCacheSize", getRecentInfoCacheSize()));
-		setRecentChunkCacheSize(rc.getInt("core", "dht", "recentChunkCacheSize", getRecentChunkCacheSize()));
 
 		setTrackFirstChunkLoad(rc.getBoolean("core", "dht", "debugTrackFirstChunkLoad", isTrackFirstChunkLoad()));
 		return this;
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ObjectIndexKey.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ObjectIndexKey.java
index b38fdcec22..ab8f8352b0 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ObjectIndexKey.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/ObjectIndexKey.java
@@ -55,7 +55,7 @@ import org.eclipse.jgit.lib.ObjectId;
 
 /** Identifies an ObjectId in the DHT. */
 public final class ObjectIndexKey extends ObjectId implements RowKey {
-	private static final int KEYLEN = 52;
+	private static final int KEYLEN = 49;
 
 	/**
 	 * @param repo
@@ -75,8 +75,8 @@ public final class ObjectIndexKey extends ObjectId implements RowKey {
 			throw new IllegalArgumentException(MessageFormat.format(
 					DhtText.get().invalidChunkKey, decode(key)));
 
-		int repo = parse32(key, 3);
-		ObjectId id = ObjectId.fromString(key, 12);
+		int repo = parse32(key, 0);
+		ObjectId id = ObjectId.fromString(key, 9);
 		return new ObjectIndexKey(repo, id);
 	}
 
@@ -106,13 +106,9 @@ public final class ObjectIndexKey extends ObjectId implements RowKey {
 
 	public byte[] asBytes() {
 		byte[] r = new byte[KEYLEN];
-		copyTo(r, 12);
-		format32(r, 3, repo);
-		// bucket is the leading 2 digits of the SHA-1.
-		r[11] = '.';
-		r[2] = '.';
-		r[1] = r[12 + 1];
-		r[0] = r[12 + 0];
+		format32(r, 0, repo);
+		r[8] = '.';
+		copyTo(r, 9);
 		return r;
 	}
 
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/OpenQueue.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/OpenQueue.java
index e47f2b2cb4..32b22340d1 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/OpenQueue.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/OpenQueue.java
@@ -159,6 +159,7 @@ final class OpenQueue<T extends ObjectId> extends QueueObjectLookup<T>
 
 	@Override
 	public void release() {
+		reader.getRecentChunks().setMaxBytes(reader.getOptions().getChunkLimit());
 		prefetcher = null;
 		currChunk = null;
 	}
@@ -173,8 +174,13 @@ final class OpenQueue<T extends ObjectId> extends QueueObjectLookup<T>
 				list = new ArrayList<ObjectWithInfo<T>>();
 				byChunk.put(chunkKey, list);
 
-				if (prefetcher == null)
-					prefetcher = new Prefetcher(reader, 0);
+				if (prefetcher == null) {
+					int limit = reader.getOptions().getChunkLimit();
+					int ratio = reader.getOptions().getOpenQueuePrefetchRatio();
+					int prefetchLimit = (int) (limit * (ratio / 100.0));
+					reader.getRecentChunks().setMaxBytes(limit - prefetchLimit);
+					prefetcher = new Prefetcher(reader, 0, prefetchLimit);
+				}
 				prefetcher.push(chunkKey);
 			}
 			list.add(c);
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/PackChunk.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/PackChunk.java
index c0684022f3..66d3d3386b 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/PackChunk.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/PackChunk.java
@@ -291,7 +291,7 @@ public final class PackChunk {
 	}
 
 	int findOffset(RepositoryKey repo, AnyObjectId objId) {
-		if (key.getRepositoryId() == repo.asInt())
+		if (key.getRepositoryId() == repo.asInt() && index != null)
 			return index.findOffset(objId);
 		return -1;
 	}
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/Prefetcher.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/Prefetcher.java
index 743f1f5944..fef2b4f29d 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/Prefetcher.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/Prefetcher.java
@@ -104,7 +104,7 @@ class Prefetcher implements StreamingCallback<Collection<PackChunk.Members>> {
 
 	private DhtException error;
 
-	Prefetcher(DhtReader reader, int objectType) {
+	Prefetcher(DhtReader reader, int objectType, int prefetchLimitInBytes) {
 		this.db = reader.getDatabase();
 		this.stats = reader.getStatistics();
 		this.objectType = objectType;
@@ -113,7 +113,7 @@ class Prefetcher implements StreamingCallback<Collection<PackChunk.Members>> {
 		this.queue = new LinkedList<ChunkKey>();
 		this.followEdgeHints = reader.getOptions().isPrefetchFollowEdgeHints();
 		this.averageChunkSize = reader.getInserterOptions().getChunkSize();
-		this.highWaterMark = reader.getOptions().getPrefetchLimit();
+		this.highWaterMark = prefetchLimitInBytes;
 
 		int lwm = (highWaterMark / averageChunkSize) - 4;
 		if (lwm <= 0)
diff --git a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/RecentChunks.java b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/RecentChunks.java
index f75e3bdc82..22608ee1b3 100644
--- a/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/RecentChunks.java
+++ b/org.eclipse.jgit.storage.dht/src/org/eclipse/jgit/storage/dht/RecentChunks.java
@@ -44,6 +44,7 @@
 package org.eclipse.jgit.storage.dht;
 
 import java.io.IOException;
+import java.util.HashMap;
 
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.ObjectLoader;
@@ -55,9 +56,11 @@ final class RecentChunks {
 
 	private final DhtReader.Statistics stats;
 
-	private final int maxSize;
+	private final HashMap<ChunkKey, Node> byKey;
 
-	private int curSize;
+	private int maxBytes;
+
+	private int curBytes;
 
 	private Node lruHead;
 
@@ -66,38 +69,56 @@ final class RecentChunks {
 	RecentChunks(DhtReader reader) {
 		this.reader = reader;
 		this.stats = reader.getStatistics();
-		this.maxSize = reader.getOptions().getRecentChunkCacheSize();
+		this.byKey = new HashMap<ChunkKey, Node>();
+		this.maxBytes = reader.getOptions().getChunkLimit();
+	}
+
+	void setMaxBytes(int newMax) {
+		maxBytes = Math.max(0, newMax);
+		if (0 < maxBytes)
+			prune();
+		else
+			clear();
 	}
 
 	PackChunk get(ChunkKey key) {
-		for (Node n = lruHead; n != null; n = n.next) {
-			if (key.equals(n.chunk.getChunkKey())) {
-				hit(n);
-				stats.recentChunks_Hits++;
-				return n.chunk;
-			}
+		Node n = byKey.get(key);
+		if (n != null) {
+			hit(n);
+			stats.recentChunks_Hits++;
+			return n.chunk;
 		}
 		stats.recentChunks_Miss++;
 		return null;
 	}
 
 	void put(PackChunk chunk) {
-		for (Node n = lruHead; n != null; n = n.next) {
-			if (n.chunk == chunk) {
-				hit(n);
-				return;
-			}
+		Node n = byKey.get(chunk.getChunkKey());
+		if (n != null && n.chunk == chunk) {
+			hit(n);
+			return;
 		}
 
-		Node n;
-		if (curSize < maxSize) {
-			n = new Node();
-			curSize++;
-		} else {
-			n = lruTail;
-		}
+		curBytes += chunk.getTotalSize();
+		prune();
+
+		n = new Node();
 		n.chunk = chunk;
-		hit(n);
+		byKey.put(chunk.getChunkKey(), n);
+		first(n);
+	}
+
+	private void prune() {
+		while (maxBytes < curBytes) {
+			Node n = lruTail;
+			if (n == null)
+				break;
+
+			PackChunk c = n.chunk;
+			curBytes -= c.getTotalSize();
+			byKey.remove(c.getChunkKey());
+			remove(n);
+		}
 	}
 
 	ObjectLoader open(RepositoryKey repo, AnyObjectId objId, int typeHint)
@@ -164,9 +185,10 @@ final class RecentChunks {
 	}
 
 	void clear() {
-		curSize = 0;
+		curBytes = 0;
 		lruHead = null;
 		lruTail = null;
+		byKey.clear();
 	}
 
 	private void hit(Node n) {