Spanner
^^^^^^^

`Cloud Spanner`_ is the world's first fully managed relational database service
to offer both strong consistency and horizontal scalability for
mission-critical online transaction processing (OLTP) applications. With Cloud
Spanner you enjoy all the traditional benefits of a relational database; but
unlike any other relational database service, Cloud Spanner scales horizontally
to hundreds or thousands of servers to handle the biggest transactional
workloads.

.. _Cloud Spanner: https://cloud.google.com/spanner/

.. toctree::
  :maxdepth: 1
  :titlesonly:
  :hidden:

  instance-usage
  database-usage
  batch-usage
  snapshot-usage
  transaction-usage
  advanced-session-pool-topics
  api-reference

Installation
============

Install the ``google-cloud-spanner`` library using ``pip``:

.. code-block:: console

    $ pip install google-cloud-spanner

Spanner Client
==============

.. _spanner-client:


Instantiating a Client
----------------------

To use the API, the :class:`~google.cloud.spanner.client.Client`
class defines a high-level interface which handles authorization
and creating other objects:

.. code:: python

    from google.cloud import spanner
    client = spanner.Client()

Long-lived Defaults
-------------------

When creating a :class:`~google.cloud.spanner.client.Client`, the
``user_agent`` and ``timeout_seconds`` arguments have sensible
defaults
(:data:`~google.cloud.spanner.client.DEFAULT_USER_AGENT` and
:data:`~google.cloud.spanner.client.DEFAULT_TIMEOUT_SECONDS`).
However, you may over-ride them and these will be used throughout all API
requests made with the ``client`` you create.

Configuration
-------------

- For an overview of authentication in ``google.cloud-python``,
  see :doc:`/core/auth`.

- In addition to any authentication configuration, you can also set the
  :envvar:`GCLOUD_PROJECT` environment variable for the Google Cloud Console
  project you'd like to interact with. If your code is running in Google App
  Engine or Google Compute Engine the project will be detected automatically.
  (Setting this environment variable is not required, you may instead pass the
  ``project`` explicitly when constructing a
  :class:`~google.cloud.storage.client.Client`).

- After configuring your environment, create a
  :class:`~google.cloud.storage.client.Client`

  .. code::

     >>> from google.cloud import spanner
     >>> client = spanner.Client()

  or pass in ``credentials`` and ``project`` explicitly

  .. code::

     >>> from google.cloud import spanner
     >>> client = spanner.Client(project='my-project', credentials=creds)

.. tip::

    Be sure to use the **Project ID**, not the **Project Number**.

Warnings about Multiprocessing
-------------------------------------------------
- When using multiprocessing, the application may hang if a
  :class:~google.cloud.spanner_v1.client.Client instance is created before
  :class:multiprocessing.Pool or :class:multiprocessing.Process invokes :func:os.fork.
  The issue is under investigation, but may be only happening on Macintosh and not Linux.
  See `GRPC/GRPC#12455 <https://github.com/grpc/grpc/issues/12455#issuecomment-348578950>`_ for more information.

Next Step
---------

After a :class:`~google.cloud.spanner.client.Client`, the next
highest-level object is an :class:`~google.cloud.spanner.instance.Instance`.
You'll need one before you can interact with databases.

Next, learn about the :doc:`instance-usage`.

.. _Instance Admin: https://cloud.google.com/spanner/reference/rpc/google.spanner.admin.instance.v1
.. _Database Admin: https://cloud.google.com/spanner/reference/rpc/google.spanner.admin.database.v1

Changelog
=========

For a list of all ``google-cloud-spanner`` releases:

.. toctree::
  :maxdepth: 2

  changelog
