Commits on Dec 13, 2023

1. perf: optimize isValid implementation …

   Cloud Spanner JDBC connections do not maintain a physical connection to
   Cloud Spanner, but are merely a wrapper around the underlying Java
   client library. This again uses a pool of gRPC channels to communicate
   with Cloud Spanner. This means that a single JDBC connection will never
   lose its network connection with Cloud Spanner, and checking whether it
   is valid or not by executing a query every time is not useful. Instead,
   the check should:
   1. Verify that a connection has successfully been established with Cloud
      Spanner. The result should be cached for all JDBC connections using
      the same Cloud Spanner client library instance.
   2. Verify that the connection has not been closed.
   
   The above can be achieved by checking that the dialect of the database
   that the connection is connected to has been successfully fetched. This
   result is cached in the client library, and being able to get that means
   that there has been a valid connection.
   
   This means that the isValid method will still return true if the network
   connectivity has been lost completely between the client and Cloud
   Spanner. However, this check is mostly used by connection pools to
   determine whether a connection is safe to be handed out to an
   application, and when all network connectivity has been lost, this will
   apply to all JDBC connections and not just one, meaning that the check
   is void.
   
   The original isValid check can be enabled by setting the System property
   spanner.jdbc.use_legacy_is_valid_check to true or setting the
   Environment variable SPANNER_JDBC_USE_LEGACY_IS_VALID_CHECK to true.
   
   Fixes #1443

   

   olavloite committed Dec 13, 2023
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