Add ALGORITHM and LOCK support for MySQL ALTER TABLE operations

[dereuromark]

Summary

Adds support for MySQL's ALGORITHM and LOCK clauses in ALTER TABLE operations, enabling zero-downtime schema migrations for compatible operations on MySQL 8.0+ and MariaDB 10.3+.

Why This Is Useful

Production Impact:

• Zero-downtime migrations: Using ALGORITHM=INSTANT allows adding nullable columns, dropping columns, and other compatible operations without copying the entire table
• Large table performance: On production databases with millions of rows, instant migrations complete in milliseconds instead of minutes or hours
• Explicit locking control: Developers can specify LOCK=NONE to ensure migrations don't block concurrent reads/writes

Real-world scenario:

// Before: Adding a column to a 100M row table = 30+ minutes of downtime
$table->addColumn('status', 'string')->update();

// After: Same operation = instant, no downtime
$table->addColumn('status', 'string', [
    'null' => true,
    'algorithm' => MysqlAdapter::ALGORITHM_INSTANT,
])->update();

  // Or with explicit locking control (use INPLACE for LOCK options)
  $table->addColumn('price', 'decimal', [
      'precision' => 10,
      'scale' => 2,
      'null' => true,
      'algorithm' => MysqlAdapter::ALGORITHM_INPLACE,  // ✅ INPLACE with LOCK
      'lock' => MysqlAdapter::LOCK_NONE,
  ])->update();

Implementation

Class Constants (No Magic Strings)

// Algorithm options
MysqlAdapter::ALGORITHM_DEFAULT
MysqlAdapter::ALGORITHM_INSTANT  // MySQL 8.0+ / MariaDB 10.3+
MysqlAdapter::ALGORITHM_INPLACE
MysqlAdapter::ALGORITHM_COPY

// Lock options
MysqlAdapter::LOCK_DEFAULT
MysqlAdapter::LOCK_NONE       // No locks, full concurrency
MysqlAdapter::LOCK_SHARED     // Allow reads, block writes
MysqlAdapter::LOCK_EXCLUSIVE  // Block all access

Key Features

• ✅ Validation of algorithm and lock values
• ✅ Conflict detection in batched operations
• ✅ Backward compatible (existing code unchanged)
• ✅ Case-insensitive option values
• ✅ Works with both single and batched operations
• ✅ Comprehensive test coverage (11 new tests)

Important MySQL Restriction

⚠️ ALGORITHM=INSTANT cannot be combined with explicit LOCK modes (LOCK=NONE, LOCK=SHARED, LOCK=EXCLUSIVE) due to MySQL limitations. Use either:

• ALGORITHM=INSTANT alone (recommended)
• ALGORITHM=INSTANT with LOCK=DEFAULT
• ALGORITHM=INPLACE with any LOCK option

Usage Examples

Single operation:

$table->addColumn('price', 'decimal', [
    'precision' => 10,
    'scale' => 2,
    'null' => true,
    'algorithm' => MysqlAdapter::ALGORITHM_INSTANT,
])->update();

Batched operations:

$table->addColumn('col1', 'string', [
        'algorithm' => MysqlAdapter::ALGORITHM_INSTANT,
    ])
    ->addColumn('col2', 'string', [
        'algorithm' => MysqlAdapter::ALGORITHM_INSTANT,
    ])
    ->update();

Changes

• MysqlAdapter.php: Added constants, validation, and algorithm/lock clause generation
• Column.php: Added algorithm and lock properties with getters/setters
• MysqlAdapterTest.php: Added 11 comprehensive test cases

Compatibility

• MySQL 8.0+ supports all algorithm options
• MariaDB 10.3+ supports all algorithm options
• Falls back gracefully on older versions (MySQL will use default behavior)
• Backward compatible: existing migrations work unchanged

[markstory]

Can we not duplicate all of this logic? This feels like a big smell that we're missing a better design solution. Perhaps we could have an adapter hook method at the end of executeActions() that receives both the actions and instructions. That would allow the MySqlAdapter to append the lock/algorithm clauses without having to create all this duplication.

[markstory]

Won't we be missing lock/algorithm when $adapter->addColumn() and changeColumn() are used because of where this logic is?