A number of environment variables can be used to configure the behavior of the library. There are also functions to configure this behavior in code. The environment variables are convenient when troubleshooting problems.
Endpoint Overrides
GOOGLE_CLOUD_CPP_SPANNER_DEFAULT_ENDPOINT=...: changes the default endpoint (spanner.googleapis.com) for the library. Intended for testing only.
SPANNER_EMULATOR_HOST=host:port: tells the library to connect to the specified emulator rather than the default endpoint. Intended for testing only.
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. Unless you have configured your own logging backend, you should also set GOOGLE_CLOUD_CPP_ENABLE_CLOG to produce any output on the program's console.
See Also
google::cloud::TracingComponentsOptionGOOGLE_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.
See Also
google::cloud::GrpcTracingOptionsOptionGOOGLE_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_PROJECT=...: is used in examples and integration tests to configure the GCP project. This has no effect in the library.
GOOGLE_CLOUD_CPP_SPANNER_TEST_INSTANCE_ID=... is used in examples and integration tests to, well, configure the spanner instance. This has no effect in the library.
GOOGLE_CLOUD_CPP_SPANNER_TEST_SERVICE_ACCOUNT=...: is used in examples and integration tests to set the service account for testing IAM operations. This has no effect in the library.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-22 UTC."],[[["\u003cp\u003eThis document details environment variables and configuration options for the C++ Spanner library, covering versions from 2.11.0 up to the latest release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eYou can override the default endpoint for the library using \u003ccode\u003eGOOGLE_CLOUD_CPP_SPANNER_DEFAULT_ENDPOINT\u003c/code\u003e, or connect to a local emulator with \u003ccode\u003eSPANNER_EMULATOR_HOST\u003c/code\u003e, which are both primarily for testing purposes.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eSPANNER_OPTIMIZER_VERSION\u003c/code\u003e and \u003ccode\u003eSPANNER_OPTIMIZER_STATISTICS_PACKAGE\u003c/code\u003e environment variables allow you to set the default query optimizer settings for \u003ccode\u003eClient::ExecuteQuery()\u003c/code\u003e calls.\u003c/p\u003e\n"],["\u003cp\u003eTracing for gRPC calls can be enabled by setting \u003ccode\u003eGOOGLE_CLOUD_CPP_ENABLE_TRACING=rpc\u003c/code\u003e and further modified with \u003ccode\u003eGOOGLE_CLOUD_CPP_TRACING_OPTIONS\u003c/code\u003e, while \u003ccode\u003eGOOGLE_CLOUD_CPP_ENABLE_CLOG=yes\u003c/code\u003e activates logging in the library.\u003c/p\u003e\n"],["\u003cp\u003eSeveral other environment variables like \u003ccode\u003eGOOGLE_CLOUD_PROJECT\u003c/code\u003e, \u003ccode\u003eGOOGLE_CLOUD_CPP_SPANNER_TEST_INSTANCE_ID\u003c/code\u003e and \u003ccode\u003eGOOGLE_CLOUD_CPP_SPANNER_TEST_SERVICE_ACCOUNT\u003c/code\u003e are mentioned as being used in tests and examples, however they do not effect the library itself.\u003c/p\u003e\n"]]],[],null,[]]
