Do not retain commit body in RevWalk for reachability checks

Commit body contains the message that is not needed for reachability checks, and
takes up memory unnecessarily.

Change-Id: I0c7f6da249bf9c4fda9dc9e62e809322c68effce
Signed-off-by: Minh Thai <mthai@google.com>

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

@@ -315,6 +315,7 @@ public class DfsReftableDatabase extends DfsRefDatabase {
 			throws IOException {
 		ReceiveCommand cmd = toCommand(oldRef, newRef);
 		try (RevWalk rw = new RevWalk(getRepository())) {
+			rw.setRetainBody(false);
 			newBatchUpdate().setAllowNonFastForwards(true).addCommand(cmd)
 					.execute(rw, NullProgressMonitor.INSTANCE);
 		}

org.eclipse.jgit/src/org/eclipse/jgit/lib/RefUpdate.java

@@ -599,6 +599,7 @@ public abstract class RefUpdate {
 	 */
 	public Result update() throws IOException {
 		try (RevWalk rw = new RevWalk(getRepository())) {
+			rw.setRetainBody(false);
 			return update(rw);
 		}
 	}
@@ -646,6 +647,7 @@ public abstract class RefUpdate {
 	 */
 	public Result delete() throws IOException {
 		try (RevWalk rw = new RevWalk(getRepository())) {
+			rw.setRetainBody(false);
 			return delete(rw);
 		}
 	}

org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java

@@ -489,6 +489,7 @@ public abstract class Repository implements AutoCloseable {
 			throws AmbiguousObjectException, IncorrectObjectTypeException,
 			RevisionSyntaxException, IOException {
 		try (RevWalk rw = new RevWalk(this)) {
+			rw.setRetainBody(false);
 			Object resolved = resolve(rw, revstr);
 			if (resolved instanceof String) {
 				final Ref ref = findRef((String) resolved);
@@ -515,6 +516,7 @@ public abstract class Repository implements AutoCloseable {
 	public String simplify(String revstr)
 			throws AmbiguousObjectException, IOException {
 		try (RevWalk rw = new RevWalk(this)) {
+			rw.setRetainBody(true);
 			Object resolved = resolve(rw, revstr);
 			if (resolved != null)
 				if (resolved instanceof String)

org.eclipse.jgit/src/org/eclipse/jgit/transport/BasePackFetchConnection.java

@@ -272,6 +272,7 @@ public abstract class BasePackFetchConnection extends BasePackConnection
 
 		if (local != null) {
 			walk = new RevWalk(local);
+			walk.setRetainBody(false);
 			reachableCommits = new RevCommitList<>();
 			REACHABLE = walk.newFlag("REACHABLE"); //$NON-NLS-1$
 			COMMON = walk.newFlag("COMMON"); //$NON-NLS-1$

org.eclipse.jgit/src/org/eclipse/jgit/transport/BaseReceivePack.java

@@ -314,6 +314,7 @@ public abstract class BaseReceivePack {
 	protected BaseReceivePack(Repository into) {
 		db = into;
 		walk = new RevWalk(db);
+		walk.setRetainBody(false);
 
 		TransferConfig tc = db.getConfig().get(TransferConfig.KEY);
 		objectChecker = tc.newReceiveObjectChecker();

org.eclipse.jgit/src/org/eclipse/jgit/transport/FetchProcess.java

@@ -200,6 +200,7 @@ class FetchProcess {
 				.setAllowNonFastForwards(true)
 				.setRefLogMessage("fetch", true); //$NON-NLS-1$
 		try (RevWalk walk = new RevWalk(transport.local)) {
+			walk.setRetainBody(false);
 			if (monitor instanceof BatchingProgressMonitor) {
 				((BatchingProgressMonitor) monitor).setDelayStart(
 						250, TimeUnit.MILLISECONDS);