GitHub user ewencp opened a pull request:

    https://github.com/apache/kafka/pull/3380

    MINOR: Add serialized vagrant rsync until upstream fixes broken parallelism

    See https://github.com/mitchellh/vagrant/issues/7531. The core of the issue 
is that vagrant rsync uses a fixed set of 1000 possible temp file entries for 
SSH ControlMaster files to cache SSH connections for rsyncing. A few notes:
    
    * We can't break down the steps further and maintain performance due to 
various limitations in vagrant/vagrant-aws (rsync is only executed on `vagrant 
up`/`vagrant reload`/`vagrant rsync`, you can't enable/disable and rsync shared 
folder only during some of those stages, and provisioning only runs in parallel 
with vagrant-aws during `vagrant up`).
    * We need to isolate each of the serialized rsync calls. (If we assumed 
`parallel` was available, we actually could get the parallelism back.) This is 
required because even across calls they could randomly choose the same 
temporary file.
    * If there's a chance multiple instances were running on the same server at 
the same or nearly the same time, they can conflict since the same temp file 
entries are used globally. This means anything running on shared CI servers 
might end up syncing data between different CI jobs (!!), which could lead to 
some very strange results. Especially weird if they aren't even for the same 
type of job.
    * Provisioning error check needs to be removed because it is catching rsync 
errors, but those can still happen in the initial `vagrant up` rsync step 
before the `vagrant up` provisioning step. It seems likely this bug was the 
cause of missing files anyway so this check might not be as valuable anymore.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/ewencp/kafka deparallelize-rsync

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/kafka/pull/3380.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #3380
    
----
commit 96d68f6141d3b84d6c8622f3212e29ee2d0db726
Author: Ewen Cheslack-Postava <m...@ewencp.org>
Date:   2017-06-20T01:58:32Z

    MINOR: Add serialized vagrant rsync until upstream fixes broken parallelism
    
    See https://github.com/mitchellh/vagrant/issues/7531

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