Changes

v1.2.0

Support tracking stacktrace of sessionPool.take() that allows the user to instruct the session pool to keep track of the stacktrace of each goroutine that checks out a session from the pool. This is disabled by default, but it can be enabled by setting SessionPoolConfig.TrackSessionHandles: true.
Add resource-based routing that includes a step to retrieve the instance-specific endpoint before creating the session client when creating a new spanner client. This is disabled by default, but it can be enabled by setting GOOGLE_CLOUD_SPANNER_ENABLE_RESOURCE_BASED_ROUTING.
Make logger configurable so that the Spanner client can now be configured to use a specific logger instead of the standard logger.
Support encoding custom types that point back to supported basic types.
Allow decoding Spanner values to custom types that point back to supported types.

The String() method of NullString, NullTime and NullDate will now return an unquoted string instead of a quoted string. This is a BREAKING CHANGE. If you relied on the old behavior, please use fmt.Sprintf(“%q”, T).
The Spanner client will now use the new BatchCreateSessions RPC to initialize the session pool. This will improve the startup time of clients that are initialized with a minimum number of sessions greater than zero (i.e. SessionPoolConfig.MinOpened>0).
Spanner clients that are created with the NewClient method will now default to a minimum of 100 opened sessions in the pool (i.e. SessionPoolConfig.MinOpened=100). This will improve the performance of the first transaction/query that is executed by an application, as a session will normally not have to be created as part of the transaction. Spanner clients that are created with the NewClientWithConfig method are not affected by this change.
Spanner clients that are created with the NewClient method will now default to a write sessions fraction of 0.2 in the pool (i.e. SessionPoolConfig.WriteSessions=0.2). Spanner clients that are created with the NewClientWithConfig method are not affected by this change.
The session pool maintenance worker has been improved so it keeps better track of the actual number of sessions needed. It will now less often delete and re-create sessions. This can improve the overall performance of applications with a low transaction rate.