pt-archiver doesn't reconnect and retry its SELECT queries
pt-archiver queries are likely to be killed by automatic query killers. (Ask me how I know.) The tool then exits with a message such as the following:
DBD::mysql::st execute failed: Lost connection to MySQL server during query [for Statement "SELECT /*!40001 SQL_NO_CACHE ...
Where the code in question is the $get_sth execute here:
PTDEBUG && _d('Fetching rows in next chunk');
my $select_start = time;
PTDEBUG && _d('Fetched', $get_sth->rows, 'rows');
This makes the tool not very resilient. I think it should catch errors there and reconnect, then try again --retries times.