DfsInserter: Optionally disable existing object check

When using a DfsInserter for high-throughput insertion of many
objects (analogous to git-fast-import), we don't necessarily want to
do a random object lookup for each. It'll be faster from the
inserter's perspective to insert the duplicate objects and let a later
GC handle the deduplication.

Change-Id: Ic97f5f01657b4525f157e6df66023f1f07fc1851

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsInserterTest.java

@@ -219,6 +219,37 @@ public class DfsInserterTest {
 		assertTrue(pack_sources.contains(PackSource.INSERT));
 	}
 
+	@Test
+	public void testNoCheckExisting() throws IOException {
+		byte[] contents = Constants.encode("foo");
+		ObjectId fooId;
+		try (ObjectInserter ins = db.newObjectInserter()) {
+			fooId = ins.insert(Constants.OBJ_BLOB, contents);
+			ins.flush();
+		}
+		assertEquals(1, db.getObjectDatabase().listPacks().size());
+
+		try (ObjectInserter ins = db.newObjectInserter()) {
+			((DfsInserter) ins).checkExisting(false);
+			assertEquals(fooId, ins.insert(Constants.OBJ_BLOB, contents));
+			ins.flush();
+		}
+		assertEquals(2, db.getObjectDatabase().listPacks().size());
+
+		// Verify that we have a foo in both INSERT packs.
+		DfsReader reader = new DfsReader(db.getObjectDatabase());
+		DfsPackFile packs[] = db.getObjectDatabase().getPacks();
+
+		assertEquals(2, packs.length);
+		DfsPackFile p1 = packs[0];
+		assertEquals(PackSource.INSERT, p1.getPackDescription().getPackSource());
+		assertTrue(p1.hasObject(reader, fooId));
+
+		DfsPackFile p2 = packs[1];
+		assertEquals(PackSource.INSERT, p2.getPackDescription().getPackSource());
+		assertTrue(p2.hasObject(reader, fooId));
+	}
+
 	private static String readString(ObjectLoader loader) throws IOException {
 		return RawParseUtils.decode(readStream(loader));
 	}

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java

@@ -106,6 +106,7 @@ public class DfsInserter extends ObjectInserter {
 	DfsPackDescription packDsc;
 	PackStream packOut;
 	private boolean rollback;
+	private boolean checkExisting = true;
 
 	/**
 	 * Initialize a new inserter.
@@ -117,6 +118,15 @@ public class DfsInserter extends ObjectInserter {
 		this.db = db;
 	}
 
+	/**
+	 * @param check
+	 *            if false, will write out possibly-duplicate objects without
+	 *            first checking whether they exist in the repo; default is true.
+	 */
+	public void checkExisting(boolean check) {
+		checkExisting = check;
+	}
+
 	void setCompressionLevel(int compression) {
 		this.compression = compression;
 	}
@@ -138,7 +148,7 @@ public class DfsInserter extends ObjectInserter {
 		if (objectMap != null && objectMap.contains(id))
 			return id;
 		// Ignore unreachable (garbage) objects here.
-		if (db.has(id, true))
+		if (checkExisting && db.has(id, true))
 			return id;
 
 		long offset = beginObject(type, len);