Test uniform bitmap commit selection across multiple branches

Test that the commit selection algorithm provides appropriate
coverage across all branches.

Change-Id: I82c71b52068f01e8cef2398aecfec8e144d9a68b
Signed-off-by: Terry Parker <tparker@google.com>

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/pack/GcCommitSelectionTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/pack/GcCommitSelectionTest.java
index d9b58e206fc91e88cc7caad05b043d53ac33794e..c50e88f97ca60111c95fa62e69ec77e6c58a2701 100644 (file)
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/pack/GcCommitSelectionTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/pack/GcCommitSelectionTest.java
@@ -50,6 +50,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -243,7 +244,8 @@ public class GcCommitSelectionTest extends GcTestCase {
 
                List<RevCommit> commits = Arrays.asList(m0, m1, m2, b3, m4, b5, m6, b7,
                                m8, m9);
-               PackWriterBitmapPreparer preparer = newPeparer(m9, commits);
+               PackWriterBitmapPreparer preparer = newPreparer(
+                               Collections.singleton(m9), commits, new PackConfig());
                List<BitmapCommit> selection = new ArrayList<>(
                                preparer.selectCommits(commits.size(), PackWriter.NONE));
 
@@ -267,15 +269,108 @@ public class GcCommitSelectionTest extends GcTestCase {
                return commit.create();
        }
 
-       private PackWriterBitmapPreparer newPeparer(RevCommit want,
-                       List<RevCommit> commits)
-                       throws IOException {
+       @Test
+       public void testDistributionOnMultipleBranches() throws Exception {
+               BranchBuilder[] branches = { tr.branch("refs/heads/main"),
+                               tr.branch("refs/heads/a"), tr.branch("refs/heads/b"),
+                               tr.branch("refs/heads/c") };
+               RevCommit[] tips = new RevCommit[branches.length];
+               List<RevCommit> commits = createHistory(branches, tips);
+               PackConfig config = new PackConfig();
+               config.setBitmapContiguousCommitCount(1);
+               config.setBitmapRecentCommitSpan(5);
+               config.setBitmapDistantCommitSpan(20);
+               config.setBitmapRecentCommitCount(100);
+               Set<RevCommit> wants = new HashSet<>(Arrays.asList(tips));
+               PackWriterBitmapPreparer preparer = newPreparer(wants, commits, config);
+               List<BitmapCommit> selection = new ArrayList<>(
+                               preparer.selectCommits(commits.size(), PackWriter.NONE));
+               Set<ObjectId> selected = new HashSet<>();
+               for (BitmapCommit c : selection) {
+                       selected.add(c.toObjectId());
+               }
+
+               // Verify that each branch has uniform bitmap selection coverage
+               for (RevCommit c : wants) {
+                       assertTrue(selected.contains(c.toObjectId()));
+                       int count = 1;
+                       int selectedCount = 1;
+                       RevCommit parent = c;
+                       while (parent.getParentCount() != 0) {
+                               parent = parent.getParent(0);
+                               count++;
+                               if (selected.contains(parent.toObjectId())) {
+                                       selectedCount++;
+                               }
+                       }
+                       // The selection algorithm prefers merges and will look in the
+                       // current range plus the recent commit span before selecting a
+                       // commit. Since this history has no merges, we expect the recent
+                       // span should have 100/10=10 and distant commit spans should have
+                       // 100/25=4 per 100 commit range.
+                       int expectedCount = 10 + (count - 100 - 24) / 25;
+                       assertTrue(expectedCount <= selectedCount);
+               }
+       }
+
+       private List<RevCommit> createHistory(BranchBuilder[] branches,
+                       RevCommit[] tips) throws Exception {
+               /*-
+                * Create a history like this, where branches a, b and c branch off of the main branch
+                * at commits 100, 200 and 300, and where commit times move forward alternating between
+                * branches.
+                *
+                * o...o...o...o...o      commits root,m0,m1,...,m399
+                *      \   \   \
+                *       \   \   o...     commits branch_c,c300,c301,...,c399
+                *        \   \
+                *         \   o...o...   commits branch_b,b200,b201,...,b399
+                *          \
+                *           o...o...o... commits branch_a,b100,b101,...,a399
+                */
+               List<RevCommit> commits = new ArrayList<>();
+               String[] prefixes = { "m", "a", "b", "c" };
+               int branchCount = branches.length;
+               tips[0] = addCommit(commits, branches[0], "root");
+               int counter = 0;
+
+               for (int b = 0; b < branchCount; b++) {
+                       for (int i = 0; i < 100; i++, counter++) {
+                               for (int j = 0; j <= b; j++) {
+                                       tips[j] = addCommit(commits, branches[j],
+                                                       prefixes[j] + counter);
+                               }
+                       }
+                       // Create a new branch from current value of the master branch
+                       if (b < branchCount - 1) {
+                               tips[b + 1] = addCommit(branches[b + 1],
+                                               "branch_" + prefixes[b + 1], tips[0]);
+                       }
+               }
+               return commits;
+       }
+
+       private RevCommit addCommit(List<RevCommit> commits, BranchBuilder bb,
+                       String msg, RevCommit... parents) throws Exception {
+               CommitBuilder commit = bb.commit().message(msg).add(msg, msg).tick(1);
+               if (parents.length > 0) {
+                       commit.noParents();
+                       for (RevCommit parent : parents) {
+                               commit.parent(parent);
+                       }
+               }
+               RevCommit c = commit.create();
+               tr.parseBody(c);
+               commits.add(c);
+               return c;
+       }
+
+       private PackWriterBitmapPreparer newPreparer(Set<RevCommit> wants,
+                       List<RevCommit> commits, PackConfig config) throws IOException {
                List<ObjectToPack> objects = new ArrayList<>(commits.size());
                for (RevCommit commit : commits) {
                        objects.add(new ObjectToPack(commit, Constants.OBJ_COMMIT));
                }
-               Set<ObjectId> wants = Collections.singleton((ObjectId) want);
-               PackConfig config = new PackConfig();
                PackBitmapIndexBuilder builder = new PackBitmapIndexBuilder(objects);
                return new PackWriterBitmapPreparer(
                                tr.getRepository().newObjectReader(), builder,