On Wed, Jan 7, 2009 at 10:04 AM, Shawn O. Pearce <spearce@xxxxxxxxxxx> wrote:
> Imran M Yousuf <imyousuf@xxxxxxxxx> wrote:
>> 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?
>
> Not really. You can more efficiently use JGit and reduce some of
> the overheads, but that's about it.
>
Thanks Shawn, for pointing it out and it actually does improve the
performance, for every lookup its like 200ms.
Best regards,
Imran
>> for (int i = 0; i < App.OBJECT_COUNT;
>> ++i) {
>> ObjectWalk objectWalk = new ObjectWalk(repo);
>
> 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.
>
>> Commit revision = repo.mapCommit(revObject.getId());
>> Tree versionTree = repo.mapTree(revision.getTreeId());
>> if (versionTree.existsBlob(isbn)) {
>> revisions.add(versionTree.findBlobMember(isbn).getId());
>
> 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();
> }
> }
> }
>
> --
> Shawn.
>
--
Imran M Yousuf
Entrepreneur & Software Engineer
Smart IT Engineering
Dhaka, Bangladesh
Email: imran@xxxxxxxxxxxxxxxxxxxxxx
Blog: http://imyousuf-tech.blogs.smartitengineering.com/
Mobile: +880-1711402557
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