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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-22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 page details environment variables that can configure the behavior of the Spanner C++ library, primarily for troubleshooting and testing purposes.\u003c/p\u003e\n"],["\u003cp\u003eThe latest release candidate version is 2.37.0-rc, and there are numerous prior versions listed, ranging from 2.36.0 down to 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eEnvironment variables can override default settings like the endpoint (using \u003ccode\u003eGOOGLE_CLOUD_CPP_SPANNER_DEFAULT_ENDPOINT\u003c/code\u003e or \u003ccode\u003eSPANNER_EMULATOR_HOST\u003c/code\u003e), and manage the query optimizer's version and statistics package using \u003ccode\u003eSPANNER_OPTIMIZER_VERSION\u003c/code\u003e and \u003ccode\u003eSPANNER_OPTIMIZER_STATISTICS_PACKAGE\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eLogging and tracing for gRPC calls can be enabled and customized with variables such as \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.\u003c/p\u003e\n"],["\u003cp\u003eCertain 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 primarily for testing and example purposes and do not directly impact the library's behavior.\u003c/p\u003e\n"]]],[],null,[]]
