Google Cloud Spanner C++ Client
1.23.0
A C++ Client Library for Google Cloud Spanner
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The Cloud Spanner C++ Client library offers types and functions to use Cloud Spanner from C++11 applications.
This library requires a C++11 compiler, it is supported (and tested) on multiple Linux distributions.
The following instructions show you how to perform basic tasks in Cloud Spanner using the C++ client library.
In order to use the Cloud Spanner C++ client library from your own code, you'll need to teach your build system how to fetch and compile the Cloud C++ client library. The Cloud Spanner C++ client library natively supports the Bazel and CMake build systems. We've created a minimal, "Hello world", quickstart repo that includes detailed instructions on how to compile the library for use in your application. You can fetch the source from GitHub as normal:
The following shows the code that you'll run in the google/cloud/spanner/quickstart/
directory, which should give you a taste of the Cloud Spanner C++ client library API.
The following are general notes about using the library.
There are several environment variables that can be set to configure certain behaviors in the library.
GOOGLE_CLOUD_CPP_ENABLE_CLOG=yes
turns on logging in the library, basically the library always "logs" but the logging infrastructure has no backend to actually print anything until the application sets a backend or they set this environment variable.GOOGLE_CLOUD_CPP_ENABLE_TRACING=rpc
turns on tracing for most gRPC calls, the library injects an additional Stub decorator that prints each gRPC request and response.GOOGLE_CLOUD_CPP_ENABLE_TRACING=rpc-streams
turns on tracing for streaming gRPC calls, such as Client::Read()
, Client::ExecuteQuery()
, and Client::ProfileQuery()
. This can produce a lot of output, so use with caution!GOOGLE_CLOUD_CPP_TRACING_OPTIONS=...
modifies the behavior of gRPC tracing, including whether messages will be output on multiple lines, or whether string/bytes fields will be truncated.GOOGLE_CLOUD_CPP_SPANNER_DEFAULT_ENDPOINT=...
changes the default endpoint (spanner.googleapis.com) for the library.GOOGLE_CLOUD_PROJECT=...
is used in examples and integration tests to configure the GCP project.GOOGLE_CLOUD_CPP_SPANNER_TEST_INSTANCE_ID=...
is used in examples and integration tests to, well, configure the spanner instance.GOOGLE_CLOUD_CPP_SPANNER_TEST_SERVICE_ACCOUNT=...
is used in examples and integration tests to set the service account for testing IAM operations.SPANNER_EMULATOR_HOST=host:port
tells the library to connect to the specified emulator rather than the default endpoint.SPANNER_OPTIMIZER_VERSION=n
sets the default query optimizer version to use in Client::ExecuteQuery()
calls.This library never throws exceptions to signal error. In general, the library returns a StatusOr<T>
if an error is possible. Some functions return objects that are not wrapped in a StatusOr<>
but will themselves return a StatusOr<T>
to signal an error. For example, wrappers for long running operations return future<StatusOr<T>>
, and the methods on Client
that read from a database return a RowStream
, which iterates a stream of StatusOr<T>
.
Applications should check if the StatusOr<T>
contains a value before using it, much like how you might check that a pointer is not null before dereferencing it. Indeed, a StatusOr<T>
object can be used like a smart-pointer to T
, with the main difference being that when it does not hold a T
it will instead hold a Status
object with extra information about the error.
You can check that a StatusOr<T>
contains a value by calling the .ok()
method, or by using operator bool()
(like with other smart pointers). If there is no value, you can access the contained Status
object using the .status()
member. If there is a value, you may access it by dereferencing with operator*()
or operator->()
. As with all smart pointers, callers must first check that the StatusOr<T>
contains a value before dereferencing and accessing the contained value. Alternatively, callers may instead use the .value()
member function which is defined to throw a RuntimeStatusError
if there is no value.
.value()
on a StatusOr<T>
that does not contain a value will terminate the program instead of throwing.The library automatically retries requests that fail with transient errors, and follows the recommended practices with respect to backoff between retries. Application developers can override the default retry and backoff policies.
The default policies are to continue retrying for up to 15 minutes, and to use truncated (at 5 minutes) exponential backoff, doubling the maximum backoff period between retries.