解决Gerrit的git unpack error问题
今天上午同事和我说neutron项目要换成全新的内部代码，原先仓库里的代码要全部废弃掉。于是我就简单地创建了一个空项目使用git push --force将其置空。
下午的时候，麻烦事情就来了，同事发现提交patch的时候，会发现如下报错：
remote: Resolving deltas: 100% (2/2) error: unpack failed: error Missing unknown 613fd2557fba30aff2dbd51c3807cc57561bab08 fatal: Unpack error, check server log To ssh://newptone@review.ustack.com:29418/neutron.git ! [remote rejected] HEAD -> refs/publish/datong (n/a (unpacker error)) error: failed to push some refs to 'ssh://newptone@review.ustack.com:29418/neutron.git'
通过google我找到了两篇文章：
《Gerrit Code Review - Unpack error Missing unknown》一文是说git的某object受损导致：
http://asheepapart.blogspot.jp/2011/10/gerrit-code-review-unpack-error-missing.html
我使用文提供的方法发现根本就不存在 613fd2557fba30aff2dbd51c3807cc57561bab08 object。
然后我又搜到了一个在stackoverflow上的相关提问：
http://stackoverflow.com/questions/16586642/git-unpack-error-on-push-to-gerrit
提问指出如果你使用了git 1.8 + gerrit 2.7版本的组合，就会出现这样的问题，可惜的是我所使用的git和gerrit版本均低于此。
鉴于网上没有靠谱的解决办法，只能自己去查问题所在了。先查看了gerrit的日志：
[2014-01-07 03:57:15,400] ERROR com.google.gerrit.sshd.BaseCommand : Internal server error (user newptone account 1) during git-receive-pack '/neutron.git' com.google.gerrit.sshd.BaseCommand$Failure: fatal: Unpack error, check server log at com.google.gerrit.sshd.commands.Receive.runImpl(Receive.java:157) at com.google.gerrit.sshd.AbstractGitCommand.service(AbstractGitCommand.java:106) at com.google.gerrit.sshd.AbstractGitCommand.access$000(AbstractGitCommand.java:34) at com.google.gerrit.sshd.AbstractGitCommand$1.run(AbstractGitCommand.java:72) at com.google.gerrit.sshd.BaseCommand$TaskThunk.run(BaseCommand.java:430) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) at java.util.concurrent.FutureTask.run(FutureTask.java:166) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:165) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:266) at com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:337) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:701) Caused by: java.io.IOException: Unpack error on project "neutron": AdvertiseRefsHook: org.eclipse.jgit.transport.AdvertiseRefsHookChain@77348c71class org.eclipse.jgit.transport.AdvertiseRefsHookChain at com.google.gerrit.sshd.commands.Receive.runImpl(Receive.java:156) ... 13 more Caused by: org.eclipse.jgit.errors.UnpackException: Exception while parsing pack stream at org.eclipse.jgit.transport.ReceivePack.service(ReceivePack.java:202) at org.eclipse.jgit.transport.ReceivePack.receive(ReceivePack.java:142) at com.google.gerrit.sshd.commands.Receive.runImpl(Receive.java:98) ... 13 more Caused by: org.eclipse.jgit.errors.MissingObjectException: Missing unknown 613fd2557fba30aff2dbd51c3807cc57561bab08 at org.eclipse.jgit.storage.file.WindowCursor.open(WindowCursor.java:125) at org.eclipse.jgit.lib.ObjectReader.open(ObjectReader.java:228) at org.eclipse.jgit.revwalk.RevWalk.parseAny(RevWalk.java:812) at org.eclipse.jgit.transport.BaseReceivePack.checkConnectivity(BaseReceivePack.java:956) at org.eclipse.jgit.transport.BaseReceivePack.receivePackAndCheckConnectivity(BaseReceivePack.java:756) at org.eclipse.jgit.transport.ReceivePack.service(ReceivePack.java:167) ... 15 more
那么就定义到613fd2557fba30aff2dbd51c3807cc57561bab08这串哈希值，为什么会丢失这个object ?
我顺手敲了一个 git review -l，发现gerrit上居然有一个还没有关闭的patch:
1974 master Add two interfaces for manipulate forwarding individually
我打开Gerrit web界面，点击这个patchset，跳出一段错误说明：613fd2557fba30aff2dbd51c3807cc57561bab08 cannot found.
啊哈，到这里真相就大白了。原因就是上午我在删除原先的旧有neutron代码时，忘记把gerrit上相关的neutron提交做关闭处理，而输入git review命令时，gerrit会先做一个rebase操作，再做提交，然而neutron仓库发生变化后，存在数据库中的1974号patch_set找不到对应的object了，所以在执行：git push gerrit HEAD:refs/publish/datong 操作时发生了前面的问题。
事已至此，解决的办法就是到reviewdb数据库里，先从patch_sets表中找出change_id是1974的记录，确定无误后，我们从changes表中找出对应的记录：
mysql> select * from changes where change_id=1974\G; *************************** 1. row *************************** change_key: I6596720099473969b19675f8fbb97a2db29b5532 created_on: 2014-01-06 12:20:07 last_updated_on: 2014-01-07 03:02:09 sort_key: 002a4736000007b6 owner_account_id: 25 dest_project_name: neutron dest_branch_name: refs/heads/master open: Y status: n nbr_patch_sets: 1 current_patch_set_id: 1 subject: Add two interfaces for manipulate forwarding individually topic: portforwarding-api last_sha1_merge_tested: NULL mergeable: N row_version: 2 change_id: 1974 1 row in set (0.00 sec)
我们要做的是将其关闭，并把状态置为Abandon。（友情提醒，涉及重要业务，注意备份数据库）
mysql> update changes set open='N',status='A' where change_id=1974; Query OK, 1 row affected (0.05 sec) Rows matched: 1 Changed: 1 Warnings: 0
OK，现在neutron的提交已经恢复正常，我可以安心地去做其他事情了:)
