Description

The recent release of 4.9.0 and 5.1.0 has a bug which makes MySQL backups fail. Because in this commit, the logic of when to use --single-transaction was reversed.
97da6ca#diff-83d39a4592b31403e3830a3100e22c596322d8dd9a240e07f6ecf173ec1d7bb7

Breaking change in detail

Before the commit if mysql version is newer than 5.7.41 or 8.0.32 results in FALSE

if (($isMySQL5 && version_compare($serverVersion, '5.7.41', '>=')) ||
     ($isMySQL8 && version_compare($serverVersion, '8.0.32', '>='))) {
     $useSingleTransaction = false;
 }

After the commit if mysql version is newer than 5.7.41 or 8.0.32 results in TRUE

 $useSingleTransaction =
     ($isMySQL5 && version_compare($serverVersion, '5.7.41', '>=')) ||
     ($isMySQL8 && version_compare($serverVersion, '8.0.32', '>='));

Why do we even check MySQL versions?

This check is done because after those versions, mysqldump will require the FLUSH TABLES privileges to run, which shared hosting usually will not give, as it is considered system privileges. Thus breaking any use of mysqldump. (See #12557)

Related issues

This fixes: #14922