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@@ -200,3 +200,21 @@ When using the Alpine variants, any postgres extension not listed in [postgres-c
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If there is no database when `postgres` starts in a container, then `postgres` will create the default database for you. While this is the expected behavior of `postgres`, this means that it will not accept incoming connections during that time. This may cause issues when using automation tools, such as `docker-compose`, that start several containers simultaneously.
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Also note that the default `/dev/shm` size for containers is 64MB. If the shared memory is exhausted you will encounter `ERROR: could not resize shared memory segment . . . : No space left on device`. You will want to pass [`--shm-size=256MB`](https://docs.docker.com/engine/reference/run/#runtime-constraints-on-resources) for example to `docker run`, or alternatively in [`docker-compose`](https://docs.docker.com/compose/compose-file/#shm_size)
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+
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+## Where to Store Data
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+
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+Important note: There are several ways to store data used by applications that run in Docker containers. We encourage users of the `%%IMAGE%%` images to familiarize themselves with the options available, including:
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+
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+- Let Docker manage the storage of your database data [by writing the database files to disk on the host system using its own internal volume management](https://docs.docker.com/engine/tutorials/dockervolumes/#adding-a-data-volume). This is the default and is easy and fairly transparent to the user. The downside is that the files may be hard to locate for tools and applications that run directly on the host system, i.e. outside containers.
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+- Create a data directory on the host system (outside the container) and [mount this to a directory visible from inside the container](https://docs.docker.com/engine/tutorials/dockervolumes/#mount-a-host-directory-as-a-data-volume). This places the database files in a known location on the host system, and makes it easy for tools and applications on the host system to access the files. The downside is that the user needs to make sure that the directory exists, and that e.g. directory permissions and other security mechanisms on the host system are set up correctly.
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+
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+The Docker documentation is a good starting point for understanding the different storage options and variations, and there are multiple blogs and forum postings that discuss and give advice in this area. We will simply show the basic procedure here for the latter option above:
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+
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+1. Create a data directory on a suitable volume on your host system, e.g. `/my/own/datadir`.
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+2. Start your `%%IMAGE%%` container like this:
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+
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+ ```console
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+ $ docker run --name some-%%REPO%% -v /my/own/datadir:/var/lib/postgresql/data -d %%IMAGE%%:tag
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+ ```
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+
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+The `-v /my/own/datadir:/var/lib/postgresql/data` part of the command mounts the `/my/own/datadir` directory from the underlying host system as `/var/lib/postgresql/data` inside the container, where PostgreSQL by default will write its data files.
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