4 Byte PK support

[sm745052]

This PR updates the uniform splitter to correctly handle 4-byte string characters (like emojis) in primary keys during SourceDB to Spanner migrations.
Previously, the string mapper used Java char types. Since char is limited to 2 bytes, it cannot represent 4-byte characters without surrogate pairs. Refactored CollationIndex, CollationMapper, and CollationOrderRow to use String representations instead. This removes the byte length constraints.
I also updated the MySQL and PostgreSQL collation order SQL queries to accurately handle these characters in range calculations.

To verify the fixes, I added two new integration tests that copy tables with 4-byte primary keys:

• MySQLSourceDbToSpanner4ByteStringPKIT
• PostgreSQLSourceDbToSpanner4ByteStringPKIT

Logs showing all characters were captured:

MySQL

Initialized Index ALL_POSITIONS for CollationReference{dbCharacterSet=`utf8mb4`, dbCollation=`utf8mb4_bin`, padSpace=true}, with 1112064 characters, 1112064 unique characters, and {} empty characters

PG

Initialized Index ALL_POSITIONS for CollationReference{dbCharacterSet=UTF8, dbCollation=default, padSpace=false}, with 1112063 characters, 1112063 unique characters, and {} empty characters

I increased the DirectRunner test timeout to 15 minutes in SourceDbToSpannerITBase although the tests use DataflowRunner in github actions so that we can test these tests locally using direct runner (the default timeout there was 4 min)

[gemini-code-assist]

Summary of Changes

Hello, 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 introduces support for 4-byte character sets (such as emojis) in primary keys during source database to Spanner migrations. The changes involve refining the collation order logic for both MySQL and PostgreSQL to ensure these characters are correctly processed and validated, alongside new integration tests to validate the end-to-end migration flow.

Highlights

• 4-Byte Character Support: Updated SQL collation queries for MySQL and PostgreSQL to correctly handle 4-byte UTF-8 characters (like emojis) in primary keys.
• Integration Testing: Added new integration tests for both MySQL and PostgreSQL to verify the migration of tables containing 4-byte string primary keys.

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[gemini-code-assist]

Code Review

This pull request updates the collation order queries for MySQL and PostgreSQL to support 4-byte UTF-8 characters and adds corresponding integration tests. Feedback highlights a significant performance concern in the MySQL query due to the massive increase in rows (to over 1.1 million) processed during 4-byte codepoint generation, which could cause high CPU/IO load and disk sorting. Additionally, the new integration tests should be refactored to use instance fields instead of static fields for resource managers and to declare the Dataflow job info as a local variable.

[codecov]

Codecov Report

❌ Patch coverage is 87.87879% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.87%. Comparing base (a73f5e5) to head (b14d2b8).
⚠️ Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
...niformsplitter/stringmapper/CollationOrderRow.java	50.00%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4010      +/-   ##
============================================
+ Coverage     55.74%   63.87%   +8.12%     
+ Complexity     7241     2685    -4556     
============================================
  Files          1124      556     -568     
  Lines         68476    31520   -36956     
  Branches       7726     3483    -4243     
============================================
- Hits          38173    20132   -18041     
+ Misses        27826    10353   -17473     
+ Partials       2477     1035    -1442     

Components	Coverage Δ
spanner-templates	87.54% <87.87%> (-0.13%)	⬇️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	89.24% <ø> (-0.05%)	⬇️
spanner-live-reverse-replication	83.43% <ø> (-0.04%)	⬇️
spanner-bulk-migration	92.21% <87.87%> (-0.28%)	⬇️
gcs-spanner-dv	88.52% <ø> (-0.03%)	⬇️

Files with missing lines	Coverage Δ
...c/uniformsplitter/stringmapper/CollationIndex.java	97.29% <100.00%> (+0.11%)	⬆️
.../uniformsplitter/stringmapper/CollationMapper.java	98.26% <100.00%> (+0.98%)	⬆️
...niformsplitter/stringmapper/CollationOrderRow.java	86.66% <50.00%> (-9.89%)	⬇️

... and 604 files with indirect coverage changes

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[gemini-code-assist]

Code Review

This pull request updates the collation mapping classes to use String instead of Character to support multi-byte characters (such as 4-byte UTF-8 emojis) and adds corresponding integration tests for MySQL and PostgreSQL. The review feedback highlights a critical bug where reference equality (== and !=) is used with BigInteger.ZERO instead of .equals(), which can lead to infinite loops during deserialization. Additionally, suggestions are provided to simplify padding calculations and use Java 8 streams for more idiomatic code point extraction.

[bharadwaj-aditya]

Thanks for putting this together. This flow looks a lot simpler.