Crash Recovery Simulation

The inno simulate subcommand helps you understand what would happen at each InnoDB innodb_force_recovery level before you commit to setting it in production.

When to Use

  • MySQL refuses to start after a crash and you need to choose a recovery level
  • You want to assess the risk of data loss before setting innodb_force_recovery
  • You need to document the state of a corrupted tablespace for incident response
  • You want to verify that a tablespace can survive recovery without data loss

Quick Start

# Simulate all recovery levels against your system tablespace
inno simulate -f /var/lib/mysql/ibdata1 -d /var/lib/mysql

# Focus on a specific level
inno simulate -f /var/lib/mysql/ibdata1 -d /var/lib/mysql --level 3 -v

Recovery Level Decision Tree

Start at level 1 and only increase if the previous level is insufficient:

  1. Level 1 — Try first. Skips corrupt pages but preserves all recoverable data. Safe for most single-page corruption.

  2. Level 2 — If level 1 hangs on background operations. Prevents purge and insert buffer merge.

  3. Level 3 — If crash recovery itself fails. Skips transaction rollback, which means uncommitted transactions remain visible.

  4. Level 4 — If insert buffer corruption is suspected. Skips merge operations entirely.

  5. Level 5 — If undo log is corrupted. Skips undo scanning, meaning the undo tablespace is treated as empty.

  6. Level 6 — Last resort. Skips redo log entirely. The database starts in whatever state the data files are in, ignoring any pending redo operations.

JSON Output

inno simulate -f ibdata1 -d /var/lib/mysql --json

{
  "file": "ibdata1",
  "levels": [
    {
      "level": 1,
      "name": "SRV_FORCE_IGNORE_CORRUPT",
      "survivable": true,
      "affected_pages": 2,
      "risks": ["2 corrupt pages will be skipped"]
    }
  ]
}

Workflow: Post-Crash Recovery

  1. Assess: Run inno simulate to understand the damage
  2. Back up: Copy all data files before attempting recovery
  3. Recover: Set innodb_force_recovery to the lowest effective level
  4. Export: Use mysqldump to export all data
  5. Rebuild: Restore from the dump into a fresh MySQL instance
  6. Verify: Run inno verify and inno audit on the new data directory
  • inno verify — structural integrity verification
  • inno recover — page-level recoverability assessment
  • inno checksum — checksum validation
  • inno repair — fix corrupt checksums