First iteration of the automatic task executor

[gabocic]

Works in two phases

Phase 1: Validation

• Connects to MySQL/MariaDB database server
• Retrieves database flavor and version
• Validates binary log is enabled
• Checks storage engine (must be InnoDB for Online DDL)
• Validates if Online DDL (ALGORITHM=INPLACE, LOCK=NONE) is possible
• Checks table size (rows and megabytes)

Phase 2: Execution

• Performs table backups (mysqldump, xtrabackup)
• Estimates backup size and checks that there is enough space in the filesystem
• Executes schema changes using
  • pt-online-schema-change (if requested)
  • Falls back to Online DDL when pt-online-schema-change is not used
  • Direct execution for operations that don't support Online DDL