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