source-mysql v10: preserve saved schema history so column additions don't break CDC

[tanishq171]

What

v10 of the patched source-mysql connector: preserve the saved Debezium schema history instead of unconditionally rebuilding it, so adding a column to a source table no longer breaks CDC. Built on v9 (source-mysql-gtid-patch-v9, the PR base) — this is the single schema-history commit on top of it.

Why

The v7 schema-history rebuild replaces the saved history with a fresh snapshot from live SHOW CREATE TABLE on every warm start. When a column is added on the source, that seeds the connector with the current (post-ALTER, N-column) shape, but the connector resumes from a saved binlog offset that predates the ALTER. Debezium then validates old, pre-ALTER row events (N-1 columns) against the rebuilt N-column schema and aborts:

Error processing row in <table>, internal schema size N, but row size N-1, restart connector with schema recovery mode.

Observed on testhub-015 → btcer (build_test_case_execution_results), job 18847: the rebuild jumped btcer to 83 columns while the connector was ~620 binlog files behind, so the first pre-ALTER 82-column row killed the sync — instead of Airbyte's normal auto-propagation of the new column.

The change

MySqlSourceDebeziumOperations.validate(): keep debeziumState.schemaHistory when non-empty; fall back to the SHOW CREATE TABLE rebuild only when there is no saved history to resume from. This lets Debezium replay the ALTER … ADD COLUMN from the binlog at its correct position and evolve the schema in lockstep — the stock behavior the v7 rebuild was clobbering.

Verification

• Compiles clean.
• Image boots clean (spec): tanishq171/source-mysql:3.52.3-gtid-patch-v10 (linux/amd64), digest sha256:ab2d029b392c9f062566f5970e658dab6c2279b98e81ecf4e22eaaebb0a11bcf.

Trade-off

The rebuild now runs only for empty history, so a non-empty-but-incomplete history (a table missing after a master/replica swap + retention gap — v7's original target) is no longer force-rebuilt. Accepted here in favor of not breaking column additions; revisit with a per-table merge if the swap case resurfaces.

🤖 Generated with Claude Code

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