fix: retry CreateSession also when waitForMinSessions is zero

[olavloite]

The creation of a session at startup would only be retried if waitForMinSessions was set. This changed introduces retries for CreateSession at startup if the error code is potentially transient. The number of retries is set to maximum 10.

[gemini-code-assist]

Summary of Changes

Hello @olavloite, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request improves the robustness of the Spanner client library by implementing more comprehensive retry mechanisms for session creation during application startup. It ensures that transient issues during initial session establishment are handled gracefully, preventing immediate failures. Additionally, the changes include new test coverage for transaction options and error handling during session creation, contributing to overall stability and reliability.

Highlights

• Enhanced Session Creation Retries: The CreateSession operation now includes retry logic for transient errors during startup, even when waitForMinSessions is not explicitly configured.
• Increased Initial Retry Attempts: When waitForMinSessions is zero or null, the initial CreateSession call will now attempt up to 10 retries for transient errors.
• New Test for ExcludeFromChangeStream: A new test file was added to validate the functionality of excluding transactions from change streams under various conditions, including transaction aborts and unavailable reads.
• New Test for CreateSession Deadline Exceeded: A test case was introduced to specifically verify the client's behavior when CreateSession encounters a DEADLINE_EXCEEDED error.

Changelog

• google-cloud-spanner/src/main/java/com/google/cloud/spanner/MultiplexedSessionDatabaseClient.java
  • Modified asyncCreateMultiplexedSession method signature to accept a remainingAttempts parameter.
  • Implemented retry logic within onSessionCreateFailure for transient SpannerException error codes, using the remainingAttempts count.
  • Adjusted the initial call to asyncCreateMultiplexedSession to use 10 attempts if waitForMinSessions is zero or null, otherwise 1 attempt.
  • Updated maybeWaitForSessionCreation to pass 1 as the remainingAttempts when retrying session creation.
• google-cloud-spanner/src/test/java/com/google/cloud/spanner/ExcludeFromChangeStreamTest.java
  • Added a new test file ExcludeFromChangeStreamTest.java.
  • Included tests for testStandardTransaction, testTransactionAbortedDuringRead, testTransactionAbortedDuringCommit, testReadReturnsUnavailable, and testReadReturnsUnavailableHalfway.
• google-cloud-spanner/src/test/java/com/google/cloud/spanner/MultiplexedSessionDatabaseClientMockServerTest.java
  • Added testCreateSessionDeadlineExceeded to verify handling of DEADLINE_EXCEEDED errors during CreateSession.

Activity

• The pull request was created by olavloite to address a fix for retrying CreateSession calls, specifically when waitForMinSessions is zero, to handle transient errors more effectively.

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[gemini-code-assist]

Code Review

This pull request introduces retry logic for CreateSession at startup, which is a valuable improvement for handling transient network issues. The implementation in MultiplexedSessionDatabaseClient.java is sound. I've added one suggestion to replace a magic number with a named constant to improve code maintainability. Additionally, please note that the new test file google-cloud-spanner/src/test/java/com/google/cloud/spanner/ExcludeFromChangeStreamTest.java appears to be unrelated to the scope of this pull request and may have been included unintentionally.