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
! 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：
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:
1974masterAdd 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 cannotfound.
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:
1Changed: 1Warnings: 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:)
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