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Optimize RevWalk.getMergedInto() 

Transitive Relation Definition:
On the DAG of commit history, if A can reach B, C can reach A, then C
can reach B.

Example:
As is shown in the graph below:

  1 - 2 - 3 - 4 (side)
            \
             5 -  6^ (master) - 7 (topic)

Find out which branches is 2 merged into:
After we calculated that master contains 2, we can mark 6 as TEMP_MARK
to avoid unwanted walks.
When we want to figure out if 2 is merge into the topic, the traversal
path would be [7, 6] instead of [7, 6, 5, 3, 2].

Test:
This change can significantly improve performance for tags.
On a copy of the Linux repository, the command 'git tag --contains
<commit>' had the following performance improvement:

commit      | Before   | After   | Rel %
47a44d27ca  | 29251ms  | 6687ms  | -77%
90327e7dff  | 21388ms  | 6256ms  | -70%
f85fac0efa  | 11150ms  | 7338ms  | -34%

The current version ignores tags, even though the tag is a type of
the ref.
Follow-up commits I'll fix it.

Change-Id: Ie6295ca4d16070499912af462239e679a97cce47
Signed-off-by: kylezhao <kylezhao@tencent.com>
Reviewed-by: Christian Halstrick <christian.halstrick@sap.com>
Reviewed-by: Martin Fick <mfick@codeaurora.org>
This commit is contained in:
kylezhao 2021-08-31 19:36:44 +08:00 committed by Matthias Sohn
parent c0380e9cdd
commit c5b3054735
2 changed files with 24 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/RevWalkUtilsReachableTest.java
View File

@ -82,20 +82,33 @@ public void findBranchesReachableManyTimes() throws Exception {
* a b
* | |
* c d
* | \
* f e
* | /
* g
*/
RevCommit a = commit();
RevCommit b = commit();
RevCommit c = commit(a);
RevCommit d = commit(b);
RevCommit f = commit(d);
RevCommit e = commit(d);
RevCommit g = commit(f, e);
Ref branchA = branch("a", a);
Ref branchB = branch("b", b);
Ref branchC = branch("c", c);
Ref branchD = branch("d", d);
Ref branchE = branch("e", e);
Ref branchF = branch("f", f);
Ref branchG = branch("g", g);
assertContains(a, asList(branchA, branchC));
assertContains(b, asList(branchB, branchD));
assertContains(b, asList(branchB, branchD, branchE, branchF, branchG));
assertContains(c, asList(branchC));
assertContains(d, asList(branchD));
assertContains(d, asList(branchD, branchE, branchF, branchG));
assertContains(e, asList(branchE, branchG));
assertContains(f, asList(branchF, branchG));
assertContains(g, asList(branchG));
}
private Ref branch(String name, RevCommit dst) throws Exception {

11
org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevWalk.java
View File

@ -528,6 +528,7 @@ private List<Ref> getMergedInto(RevCommit needle, Collection<Ref> haystacks,
Enum returnStrategy, ProgressMonitor monitor) throws IOException {
List<Ref> result = new ArrayList<>();
List<RevCommit> uninteresting = new ArrayList<>();
List<RevCommit> marked = new ArrayList<>();
RevFilter oldRF = filter;
TreeFilter oldTF = treeFilter;
try {
@ -545,17 +546,20 @@ private List<Ref> getMergedInto(RevCommit needle, Collection<Ref> haystacks,
continue;
}
RevCommit c = (RevCommit) o;
resetRetain(RevFlag.UNINTERESTING);
reset(UNINTERESTING | TEMP_MARK);
markStart(c);
boolean commitFound = false;
RevCommit next;
while ((next = next()) != null) {
if (References.isSameObject(next, needle)) {
if (References.isSameObject(next, needle)
|| (next.flags & TEMP_MARK) != 0) {
result.add(r);
if (returnStrategy == GetMergedIntoStrategy.RETURN_ON_FIRST_FOUND) {
return result;
}
commitFound = true;
c.flags |= TEMP_MARK;
marked.add(c);
break;
}
}
@ -571,6 +575,9 @@ private List<Ref> getMergedInto(RevCommit needle, Collection<Ref> haystacks,
roots.addAll(uninteresting);
filter = oldRF;
treeFilter = oldTF;
for (RevCommit c : marked) {
c.flags &= ~TEMP_MARK;
}
}
return result;
}