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added Compose topics on caching options for performance (#3932) 

* added Compose topics on caching options for performance

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>

* updated title for Compose topic

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>

* line wrap per review

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
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43
compose/compose-file/index.md
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@ -1426,9 +1426,50 @@ services:
constraints: [node.role == manager] constraints: [node.role == manager]
``` ```
#### Caching options for volume mounts (Docker for Mac)
On Docker 17.04 CE Edge and up, including 17.06 CE Edge and Stable, you can
configure container-and-host consistency requirements for bind-mounted
directories in Compose files to allow for better performance on read/write of
volume mounts. These options address issues specific to `osxfs` file sharing,
and therefore are only applicable on Docker for Mac.
The flags are:
* `consistent`: Full consistency. The container runtime and the
host maintain an identical view of the mount at all times. This is the default.
* `cached`: The host's view of the mount is authoritative. There may be
delays before updates made on the host are visible within a container.
* `delegated`: The container runtime's view of the mount is
authoritative. There may be delays before updates made in a container
are visible on the host.
Here is an example of configuring a volume as `cached`:
```
version: '3'
services:
php:
image: php:7.1-fpm
ports:
- 9000
volumes:
- .:/var/www/project:cached
```
Full detail on these flags, the problems they solve, and their
`docker run` counterparts is in the Docker for Mac topic [Performance tuning for
volume mounts (shared filesystems)](/docker-for-mac/osxfs-caching.md).
### restart ### restart
`no` is the default restart policy, and it will not restart a container under any circumstance. When `always` is specified, the container always restarts. The `on-failure` policy restarts a container if the exit code indicates an on-failure error. `no` is the default restart policy, and it will not restart a container under
any circumstance. When `always` is specified, the container always restarts. The
`on-failure` policy restarts a container if the exit code indicates an
on-failure error.
restart: "no" restart: "no"
restart: always restart: always

34
docker-for-mac/osxfs-caching.md
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@ -15,7 +15,22 @@ of mounted volume access on Docker for Mac. These options begin to solve some of
the challenges discussed in [Performance issues, solutions, and the challenges discussed in [Performance issues, solutions, and
roadmap](/docker-for-mac/osxfs.md#performance-issues-solutions-and-roadmap). roadmap](/docker-for-mac/osxfs.md#performance-issues-solutions-and-roadmap).
> **Tip:** Release notes for Docker CE Edge 17.04 are [here](https://github.com/moby/moby/releases/tag/v17.04.0-ce), and the associated pull request for the additional `docker run -v` flags is [here](https://github.com/moby/moby/pull/31047). > **Tip:** Release notes for Docker CE Edge 17.04 are
[here](https://github.com/moby/moby/releases/tag/v17.04.0-ce), and the
associated pull request for the additional `docker run -v` flags is
[here](https://github.com/moby/moby/pull/31047).
The following topics describe the challenges of bind-mounted volumes on `osxfs`,
and the caching options provided to optimize performance.
This blog post on [Docker on Mac
Performance](https://stories.amazee.io/docker-on-mac-performance-docker-machine-vs-docker-for-mac-4c64c0afdf99)
gives a nice, quick summary.
For information on how to configure these options in a Compose file, see
[Caching options for volume
mounts](/compose/compose-file.md#caching-options-for-volume-mounts-docker-for-mac)
the Docker Compose topics.
## Performance implications of host-container file system consistency ## Performance implications of host-container file system consistency
@ -67,9 +82,10 @@ there is no need for writes to build artifacts within the container to
be immediately reflected on the host file system. Distinguishing between be immediately reflected on the host file system. Distinguishing between
these two cases makes it possible to significantly improve performance. these two cases makes it possible to significantly improve performance.
There are three broad scenarios to consider, based on which you can dial in the level of consistency you need. In each case, the container There are three broad scenarios to consider, based on which you can dial in the
has an internally-consistent view of bind-mounted directories, but in level of consistency you need. In each case, the container has an
two cases temporary discrepancies are allowed between container and host. internally-consistent view of bind-mounted directories, but in two cases
temporary discrepancies are allowed between container and host.
* `consistent`: perfect consistency * `consistent`: perfect consistency
(host and container have an identical view of the mount at all times) (host and container have an identical view of the mount at all times)
@ -82,10 +98,12 @@ two cases temporary discrepancies are allowed between container and host.
## Examples ## Examples
Each of these configurations (`consistent`, `cached`, `delegated`) can be specified as a suffix to the [`-v`](https://docs.docker.com/engine/reference/run/#volume-shared-filesystems) Each of these configurations (`consistent`, `cached`, `delegated`) can be
option of [`docker run`](https://docs.docker.com/engine/reference/run.md). specified as a suffix to the
For example, to bind-mount `/Users/yallop/project` in a container under [`-v`](https://docs.docker.com/engine/reference/run/#volume-shared-filesystems)
the path `/project`, you might run the following command: option of [`docker run`](https://docs.docker.com/engine/reference/run.md). For
example, to bind-mount `/Users/yallop/project` in a container under the path
`/project`, you might run the following command:
``` ```
docker run -v /Users/yallop/project:/project:cached alpine command docker run -v /Users/yallop/project:/project:cached alpine command