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.
> 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.
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