What does, "FATAL: Error computing merge base" mean?

Question

I've had Jenkins running for about a year now. It builds master, rc*, and production branches. On every commit, it performs a git clone, does a bundle install, runs a migration, etc. It's been working perfectly. Recently, it has been failing and I'm getting the following traceback:

FATAL: Error computing merge base
hudson.plugins.git.GitException: Error computing merge base
  at hudson.plugins.git.util.GitUtils.filterTipBranches(GitUtils.java:149)
  at hudson.plugins.git.util.DefaultBuildChooser.getAdvancedCandidateRevisions(DefaultBuildChooser.java:201)
  at hudson.plugins.git.util.DefaultBuildChooser.getCandidateRevisions(DefaultBuildChooser.java:46)
  at hudson.plugins.git.GitSCM$2.invoke(GitSCM.java:1057)
  at hudson.plugins.git.GitSCM$2.invoke(GitSCM.java:948)
  at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2417)
  at hudson.remoting.UserRequest.perform(UserRequest.java:118)
  at hudson.remoting.UserRequest.perform(UserRequest.java:48)
  at hudson.remoting.Request$2.run(Request.java:326)
  at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
  at java.util.concurrent.FutureTask.run(FutureTask.java:166)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
  at java.lang.Thread.run(Thread.java:679)

With the following displayed immediately after:

Caused by: org.eclipse.jgit.errors.MissingObjectException: Missing commit 2faf546491565d033b1e0a79bef4b2d107447f49
  at org.eclipse.jgit.internal.storage.file.WindowCursor.open(WindowCursor.java:149)
  at org.eclipse.jgit.revwalk.RevWalk.getCachedBytes(RevWalk.java:853)
  at org.eclipse.jgit.revwalk.RevCommit.parseHeaders(RevCommit.java:142)
  at org.eclipse.jgit.revwalk.MergeBaseGenerator.next(MergeBaseGenerator.java:148)
  at org.eclipse.jgit.revwalk.StartGenerator.next(StartGenerator.java:102)
  at org.eclipse.jgit.revwalk.RevWalk.next(RevWalk.java:414)
  at hudson.plugins.git.util.GitUtils.filterTipBranches(GitUtils.java:127)
  ... 14 more

This commit error is also confusing since all branches include it.

What exactly does, "Error computing merge base mean?" and why am I getting the missing commit message?

Any insights here would be greatly appreciated.

Thanks.

git fsck:

Checking object directories: 100% (256/256), done.
Checking objects: 100% (3203/3203), done.

In my Jenkins configuration, my git plugin config is set to:

1. Wipe out workspace before build
2. Use shallow clone

I'm using Jenkins, ver. 1.528.

Answer 1

Per twalberg's comment above, disabling shallow clone solved this issue. All branches built and jobs completed.