[JGIT RFC] How read versions of a specific object

Hi,

I am trying to read all or n-th version of an object. Currently to do this I am using the following piece of code, which has to walk to every commit is present and from there prepare a set of its object id, it is definitely expensive if the commit history is huge, is there a faster/better way to achieve it?

for (int i = 0; i < App.OBJECT_COUNT;
            ++i) {
            System.out.println("INDEX: " + i);
            String isbn =
                String.valueOf(Integer.parseInt(App.INIT_ID) + i);
            System.out.println("ISBN: " + isbn);
            ObjectWalk objectWalk = new ObjectWalk(repo);
            /*
             * Checks whether the Commit has the tree or not. It does not
             * check whether it has changed or not.
             */
            objectWalk.setTreeFilter(PathFilter.create(isbn));
            RevObject revObject = null;
            objectWalk.markStart(objectWalk.parseCommit(repo.resolve(
                Constants.HEAD)));
            Set<ObjectId> revisions =
                new HashSet<ObjectId>();
            do {
                if (revObject != null) {
                    Commit revision = repo.mapCommit(revObject.getId());
                    Tree versionTree = repo.mapTree(revision.getTreeId());
                    if (versionTree.existsBlob(isbn)) {
                        revisions.add(versionTree.findBlobMember(isbn).getId());
                    }
                }
                revObject = objectWalk.next();
            }
            while (revObject != null);
            System.out.println("Revisions: " + revisions);
        }

The details source code of the project is available @ http://github.com/imyousuf/jgit-usage/tree/master

Thank you,

Imran M Yousuf <imyousuf@gmail.com> wrote:

Not really. You can more efficiently use JGit and reduce some of the overheads, but that's about it.

Don't use ObjectWalk, use a RevWalk. You don't need it to keep track of tree or blob identities. The ObjectWalk code has more overhead to do that bookkeeping.

Use a TreeWalk to do this. Its quicker because it doesn't have to parse as much data to come up with the same result.

More specifically there's a static factory method that sets up for a path limited walk and returns the TreeWalk pointing at that entry.

You can use the fact that RevWalk.next() returns a RevCommit to get you the RevTree, which is the tree you need to give to the TreeWalk constructor (its the root level tree of the commit).

But if App.OBJECT_COUNT is quite large and covers most of your objects, you are probably better off using a loop over the commits and diff'ing against the ancestor:

	final HashMap<String, Set<ObjectId>> versions = ...;
	final RevWalk rw = new RevWalk(repo);
	final TreeWalk tw = new TreeWalk(repo);
	rw.markStart(rw.parseCommit(repo.parse(HEAD)));
	tw.setFilter(TreeFilter.ANY_DIFF);

	RevCommit c;
	while ((c = rw.next()) != null) {
		final ObjectId[] p = new ObjectId[c.getParentCount() + 1];
		for (int i = 0; i < c.getParentCount(); i++) {
			rw.parse(c.getParent(i));
			p[i] = c.getParent(i).getTree();
		}
		final int me = p.length -1;
		p[me] = c.getTree();
		tw.reset(p);
		while (tw.next()) {
			if (tw.getFileMode(me).getObjectType() == Constants.OBJ_BLOB) {
				// This path was modified relative to the ancestor(s).
				//
				String s = tw.getPathString();
				Set<ObjectId> i = versions.get(s);
				if (i == null)
					versions.put(s, i = new HashSet<ObjectId>());
				i.add(tw.getObjectId(me));
			}

			if (tw.isSubtree()) {
				// make sure we recurse into modified directories
				tw.enterSubtree();
			}
		}
	}

On Wed, Jan 7, 2009 at 10:04 AM, Shawn O. Pearce <spearce@spearce.org> wrote:

Thanks Shawn, for pointing it out and it actually does improve the performance, for every lookup its like 200ms.

Best regards,

Imran