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epriestley 892a9a1f07 Make cluster repositories more resistant to freezing
Summary:
Ref T10860. This allows us to recover if the connection to the database is lost during a push.

If we lose the connection to the master database during a push, we would previously freeze the repository. This is very safe, but not very operator-friendly since you have to go manually unfreeze it.

We don't need to be quite this aggressive about freezing things. The repository state is still consistent after we've "upgraded" the lock by setting `isWriting = 1`, so we're actually fine even if we lost the global lock.

Instead of just freezing the repository immediately, sit there in a loop waiting for the master to come back up for a few minutes. If it recovers, we can release the lock and everything will be OK again.

Basically, the changes are:

  - If we can't release the lock at first, sit in a loop trying really hard to release it for a while.
  - Add a unique lock identifier so we can be certain we're only releasing //our// lock no matter what else is going on.
  - Do the version reads on the same connection holding the lock, so we can be sure we haven't lost the lock before we do that read.

Test Plan:
  - Added a `sleep(10)` after accepting the write but before releasing the lock so I could run `mysqld stop` and force this issue to occur.
  - Pushed like this:

```
$ echo D >> record && git commit -am D && git push
[master 707ecc3] D
 1 file changed, 1 insertion(+)
# Push received by "local001.phacility.net", forwarding to cluster host.
# Waiting up to 120 second(s) for a cluster write lock...
# Acquired write lock immediately.
# Waiting up to 120 second(s) for a cluster read lock on "local001.phacility.net"...
# Acquired read lock immediately.
# Device "local001.phacility.net" is already a cluster leader and does not need to be synchronized.
# Ready to receive on cluster host "local001.phacility.net".
Counting objects: 3, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 254 bytes | 0 bytes/s, done.
Total 3 (delta 1), reused 0 (delta 0)
BEGIN SLEEP
```

  - Here, I stopped `mysqld` from the CLI in another terminal window.

```
END SLEEP
# CRITICAL. Failed to release cluster write lock!
# The connection to the master database was lost while receiving the write.
# This process will spend 300 more second(s) attempting to recover, then give up.
```

  - Here, I started `mysqld` again.

```
# RECOVERED. Link to master database was restored.
# Released cluster write lock.
To ssh://local@localvault.phacility.com/diffusion/26/locktopia.git
   2cbf87c..707ecc3  master -> master
```

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10860

Differential Revision: https://secure.phabricator.com/D15792
2016-04-25 11:37:31 -07:00
bin Provide bin/nuance import and ngram indexes for sources 2016-03-08 10:30:24 -08:00
conf Support "ssl.chain" in Aphlict configuration 2016-04-14 10:41:21 -07:00
externals Improve Amazon SES code error handling behavior 2016-04-05 17:28:45 -07:00
resources Make cluster repositories more resistant to freezing 2016-04-25 11:37:31 -07:00
scripts Allow cluster devices to SSH to one another without acting as a user 2016-04-19 13:04:41 -07:00
src Make cluster repositories more resistant to freezing 2016-04-25 11:37:31 -07:00
support Support Aphlict clustering 2016-04-14 13:26:30 -07:00
webroot Give application actors in feed reasonable icons 2016-04-20 14:38:55 -07:00
.arcconfig Use the configuration driven unit test engine 2015-08-11 07:57:11 +10:00
.arclint Begin adding test coverage to GitHub Events API parsers 2016-03-09 09:30:07 -08:00
.arcunit Use the configuration driven unit test engine 2015-08-11 07:57:11 +10:00
.editorconfig Fix text lint issues 2015-02-12 07:00:13 +11:00
.gitignore Move server-related Aphlict options to a configuration file 2016-04-14 04:54:42 -07:00
LICENSE Fix text lint issues 2015-02-12 07:00:13 +11:00
NOTICE Update Phabricator NOTICE file to reflect modern legal circumstances 2014-06-25 13:42:13 -07:00
README.md Remove push to IRC from "readme.md" too 2015-10-24 18:39:16 -07:00

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