handle retryable errors in AssignShardIdFn [reverse replication]

[sm745052]

fixes b/460679219

Context:

• if the AssignShardIdFn cannot provide a shardId, then we consider it to be permanent error.
• to get the shardId we need the entire row (in multi-shard migration). However, in case of a DELETE, the ChangeStream doesnot provide the entire row. this requires a read from spanner.
• if we cannot read from spanner, we set the shardId as NULL which causes the template to consider it as a permanent error.

Solution:
Using a sentinel shard_id to identify that it was a retryable error or severe error in SourceWriterFn.

Changes:

• added constant shard ids to represent permanent and retryable errors.
• Added a spanner to sourcedb exception classifier to use it in assignshardidfn and sourcewriterfn

Extra:

• Chore: removed an unused import on AssignShardIdFn

[gemini-code-assist]

Summary of Changes

Hello @sm745052, 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 enhances the robustness of the reverse replication pipeline by refining error handling during shard ID assignment. Previously, failures to determine a shard ID were uniformly treated as permanent errors. The changes introduce a distinction between retryable and severe errors, allowing the system to appropriately tag and potentially reprocess records affected by transient issues, thereby improving the overall resilience of the data flow.

Highlights

• Improved Error Handling for Shard ID Assignment: Introduced a mechanism to differentiate between retryable and severe errors when the AssignShardIdFn fails to determine a shard ID, particularly during DELETE operations where a Spanner read is required.
• Sentinel Shard IDs: Defined two new constants, RETRYABLE_SENTINEL_SHARD_ID and SEVERE_SENTINEL_SHARD_ID, to act as flags for different error types within the data records.
• Updated Shard Assignment Logic: The AssignShardIdFn now checks if a SpannerException is retryable. If so, it assigns the RETRYABLE_SENTINEL_SHARD_ID; otherwise, it assigns the SEVERE_SENTINEL_SHARD_ID.
• Refined Error Tagging in SourceWriterFn: The SourceWriterFn has been updated to process records with RETRYABLE_SENTINEL_SHARD_ID by outputting them to a RETRYABLE_ERROR_TAG, and records with SEVERE_SENTINEL_SHARD_ID to a PERMANENT_ERROR_TAG.
• Comprehensive Test Coverage: New unit tests have been added and existing ones updated in AssignShardIdFnTest and SourceWriterFnTest to ensure correct handling of both retryable and severe Spanner exceptions and the new sentinel shard IDs.

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[codecov]

Codecov Report

❌ Patch coverage is 96.55172% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 50.80%. Comparing base (4a4a597) to head (f42fd5e).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...es/utils/SpannerToSourceDbExceptionClassifier.java	95.23%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3157      +/-   ##
============================================
+ Coverage     50.79%   50.80%   +0.01%     
- Complexity     5106     5117      +11     
============================================
  Files           975      976       +1     
  Lines         59984    59994      +10     
  Branches       6552     6555       +3     
============================================
+ Hits          30468    30480      +12     
  Misses        27375    27375              
+ Partials       2141     2139       -2     

Components	Coverage Δ
spanner-templates	71.00% <96.55%> (+0.02%)	⬆️
spanner-import-export	68.98% <ø> (-0.02%)	⬇️
spanner-live-forward-migration	80.02% <ø> (-0.02%)	⬇️
spanner-live-reverse-replication	77.72% <96.55%> (+0.07%)	⬆️
spanner-bulk-migration	88.47% <ø> (-0.02%)	⬇️

Files with missing lines	Coverage Δ
...eport/v2/templates/transforms/AssignShardIdFn.java	78.38% <100.00%> (+0.24%)	⬆️
...leport/v2/templates/transforms/SourceWriterFn.java	86.66% <100.00%> (+2.10%)	⬆️
...es/utils/SpannerToSourceDbExceptionClassifier.java	95.23% <95.23%> (ø)

... and 3 files with indirect coverage changes

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[bharadwaj-aditya]

LGTM

[bharadwaj-aditya]

This logic should be made uniform in other templates/flows as well. Please create a follow up task to take up that exercise.

[sm745052]

created b/472217883