I occasionally see customers who are taking backups from their PXC clusters that complain that the cluster “stalls” during the backup. As I wrote about in a previous blog post, often these stalls are really just Flow Control. But why would a backup cause Flow control?
Most backups I know of (even Percona XtraBackup) take a FLUSH TABLES WITH READ LOCK (FTWRL) at some point in the backup process. This can be disabled in XtraBackup (in certain circumstances), but it is enabled by[Read more...]