PXC-4799 : PXC member used for backups fails with Inconsistency when … #5809
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…pending DDL clashes with FTRWL". Draft fix for local deadlock issue. Ensure that CREATE TABLE statement (and other DDL statements) acquires protection against Backup Lock first (i.e. IX lock on BACKUP_LOCK MDL singleton) and only then tries to acquire protection against Global Read Lock (i.e. IX lock on GLOBAL MDL singleton) and not vice versa. This allows to avoid deadlock which sometimes occured and resulted in CREATE TABLE failure with appropriate error when mydumper backup tool was run concurrently. This (as well as some other) backup tool does LOCK INSTANCE FOR BACKUP first (which acquires S lock on BACKUP_LOCK singleton) and then does FLUSH TABLES WITH READ LOCK (which acquires S lock on GLOBAL MDL singleton). Acquiring conflicting lock in opposite order is deadlock-prone.
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…pending DDL clashes with FTRWL".
Draft fix for local deadlock issue.
Ensure that CREATE TABLE statement (and other DDL statements) acquires protection against Backup Lock first (i.e. IX lock on BACKUP_LOCK MDL singleton) and only then tries to acquire protection against Global Read Lock (i.e. IX lock on GLOBAL MDL singleton) and not vice versa.
This allows to avoid deadlock which sometimes occured and resulted in CREATE TABLE failure with appropriate error when mydumper backup tool was run concurrently. This (as well as some other) backup tool does LOCK INSTANCE FOR BACKUP first (which acquires S lock on BACKUP_LOCK singleton) and then does FLUSH TABLES WITH READ LOCK (which acquires S lock on GLOBAL MDL singleton). Acquiring conflicting lock in opposite order is deadlock-prone.