[JGIT PATCH 5/9] Arrange pack files in recency order to improve quick hits

["Shawn O. Pearce" <spearce@spearce.org>]

Packs with newer modification dates are more likely to contain data
related to recent commits, and thus will have a better probability
of containing an object we care about when we are looking only at
recent history.

In some cases, this may permit JGit to avoid reading a very large
historical pack's index file into memory if the only data we ever
need is available in newer pack files.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
 .../src/org/spearce/jgit/lib/PackFile.java         |   11 +++++++++++
 .../src/org/spearce/jgit/lib/Repository.java       |    1 +
 2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
index 3542560..7a16bf7 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
@@ -43,6 +43,7 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.Collections;
+import java.util.Comparator;
 import java.util.Iterator;
 import java.util.zip.CRC32;
 import java.util.zip.CheckedOutputStream;
@@ -57,10 +58,19 @@
  * objects are similar.
  */
 public class PackFile implements Iterable<PackIndex.MutableEntry> {
+	/** Sorts PackFiles to be most recently created to least recently created. */
+	public static Comparator<PackFile> SORT = new Comparator<PackFile>() {
+		public int compare(final PackFile a, final PackFile b) {
+			return b.packLastModified - a.packLastModified;
+		}
+	};
+
 	private final File idxFile;
 
 	private final WindowedFile pack;
 
+	private int packLastModified;
+
 	private PackIndex loadedIdx;
 
 	private PackReverseIndex reverseIdx;
@@ -75,6 +85,7 @@
 	 */
 	public PackFile(final File idxFile, final File packFile) {
 		this.idxFile = idxFile;
+		this.packLastModified = (int) (packFile.lastModified() >> 10);
 		pack = new WindowedFile(packFile) {
 			@Override
 			protected void onOpen() throws IOException {
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/Repository.java b/org.spearce.jgit/src/org/spearce/jgit/lib/Repository.java
index b9c7b2e..96c62df 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/Repository.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/Repository.java
@@ -823,6 +823,7 @@ public void scanForPacks() {
 			scanForPacks(new File(d, "pack"), p);
 		final PackFile[] arr = new PackFile[p.size()];
 		p.toArray(arr);
+		Arrays.sort(arr, PackFile.SORT);
 		synchronized (this) {
 			packFileList = arr;
 		}
-- 
1.6.2.rc0.204.gf6b427