[jiangzzhu]

Summary

Makes InitializeDoFn.createFakeParentPartition() idempotent under overlapping or retried InitializeDoFn executions during pipeline startup:

• Problem: Because DoFn execution has at-least-once semantics, two workers can execute InitializeDoFn concurrently during job startup before the first CREATE TABLE IF NOT EXISTS DDL operation completes. Both executions observe partitionMetadataDao.tableExists() == false, both execute createPartitionMetadataTable() (CREATE TABLE IF NOT EXISTS), and both proceed to createFakeParentPartition(), causing the second execution to fail with SpannerException: ALREADY_EXISTS: Row [Parent0] ... already exists.
• Fix:
  • Inside a read-write transaction (partitionMetadataDao.runInTransaction), check transaction.getPartition(...) == null before inserting each initial parent partition (consistent with ChildPartitionsRecordAction and PartitionStartRecordAction), ensuring existing Parent0 rows (and any state transitions already in progress) are never overwritten.
  • Also catch and ignore SpannerException with ErrorCode.ALREADY_EXISTS as a safeguard against concurrent insert races.

Testing

• Updated and expanded unit tests in InitializeDoFnTest covering new insertions, pre-existing initial partitions (single and TVF list), ErrorCode.ALREADY_EXISTS handling, and non-ALREADY_EXISTS exception propagation.