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::LoggingComponentsOptionGOOGLE_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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-22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 page details environment variables and their effects on the C++ Spanner library, with a focus on troubleshooting, testing, and configuring library behaviors.\u003c/p\u003e\n"],["\u003cp\u003eThe latest available version of the C++ Spanner library documentation is \u003ccode\u003e2.37.0-rc\u003c/code\u003e, with a comprehensive list of previous versions back to \u003ccode\u003e2.11.0\u003c/code\u003e, each linking to its corresponding documentation.\u003c/p\u003e\n"],["\u003cp\u003eEnvironment variables like \u003ccode\u003eGOOGLE_CLOUD_CPP_SPANNER_DEFAULT_ENDPOINT\u003c/code\u003e and \u003ccode\u003eSPANNER_EMULATOR_HOST\u003c/code\u003e can override the default endpoint and direct connections to an emulator, 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 enable customization of the query optimizer for \u003ccode\u003eClient::ExecuteQuery()\u003c/code\u003e calls.\u003c/p\u003e\n"],["\u003cp\u003eTracing and logging within the library can be controlled via \u003ccode\u003eGOOGLE_CLOUD_CPP_ENABLE_TRACING\u003c/code\u003e, \u003ccode\u003eGOOGLE_CLOUD_CPP_TRACING_OPTIONS\u003c/code\u003e, and \u003ccode\u003eGOOGLE_CLOUD_CPP_ENABLE_CLOG\u003c/code\u003e, allowing for detailed diagnostics and monitoring of gRPC calls.\u003c/p\u003e\n"]]],[],null,[]]
