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Custom Retry Policy

The Spanner Cassandra driver provides a custom retry policy that is tailored for interacting with Spanner. This policy, com.google.cloud.spanner.adapter.SpannerCqlRetryPolicy, extends the default retry behavior of the DataStax Java driver to intelligently handle Spanner-specific transient errors.

Why Use a Custom Retry Policy?

Spanner may return specific ReadFailure/WriteFailure messages for transient issues that are safe to retry. The default retry policies in the DataStax driver are not aware of these Spanner-specific errors. The SpannerCqlRetryPolicy inspects the error messages from Spanner and will trigger a retry for errors that are known to be transient. This improves the resilience of your application and helps it recover from temporary server-side issues without propagating the error to the application layer.

The policy currently retries on the following error messages:

  • HTTP/2 error code: INTERNAL_ERROR
  • Connection closed with unknown cause
  • Received unexpected EOS on DATA frame from server
  • stream terminated by RST_STREAM
  • Authentication backend internal server error. Please retry.
  • DEADLINE_EXCEEDED
  • ABORTED
  • RESOURCE_EXHAUSTED
  • UNAVAILABLE

The policy will retry up to 10 times before re-throwing the exception.

How to Configure the Retry Policy

You can configure the retry policy in your application.conf file. This file is loaded by the DataStax driver when the CqlSession is created. You need to specify the custom retry policy class for the execution profiles that you want to use it.

Here is an example of how to set the SpannerCqlRetryPolicy as the default retry policy:

datastax-java-driver {
  advanced.retry-policy {
    class = com.google.cloud.spanner.adapter.SpannerCqlRetryPolicy
  }
  ...
}

You can also configure the policy programmatically in Java:

import com.google.cloud.spanner.adapter.SpannerCqlRetryPolicy;
...
CqlSession session =
        SpannerCqlSession.builder()
            .setDatabaseUri("projects/your_project/instances/your_instance/databases/your_db")
            .addContactEndPoint(yourEndpoint) 
            .withLocalDatacenter("datacenter1")
            .withConfigLoader(
                DriverConfigLoader.programmaticBuilder()
                    .withString(DefaultDriverOption.PROTOCOL_VERSION, "V4")
                    .withClass(DefaultDriverOption.RETRY_POLICY_CLASS, SpannerCqlRetryPolicy.class)
                    .build())
            .build();