Current description of max_slowlog_size system variable is a bit misleading https://docs.percona.com/percona-server/5.7/flexibility/slowlog_rotation.html#max_slowlog_size . Currently documentation doesn’t mention Block Size=4096. A value that is not an integer multiple of this block size is rounded down to the next lower multiple of the block size. As a result, attempt to set max_slowlog_size to a value less than 4096 will lead to zero resulting value. This behavior is not clear without directly mentioning this in docs. Please see MySQLs docs for audit_log_max_size as an example

https://dev.mysql.com/doc/refman/8.4/en/audit-log-reference.html#sysvar_audit_log_max_size

https://dev.mysql.com/doc/refman/8.4/en/server-system-variables.html#system-variables-block-size