Changes in MySQL 8.0 + (max_connections / 5) . The  back_log  queues up incoming IP connect requests in situations where the server is not able to keep up with incoming requests. In the worst case, with max_connections  number of clients trying to reconnect at the same time, for example after a network failure, they can all be buffered and reject-retry loops are avoided. InnoDB Defaults 280 • Incompatible change  The default value of the  innodb_autoinc_lock_mode  system variable changed from  1  (consecutive) to  2  (interleaved). The change to interleaved lock mode as the default setting reflects the change from statement-based to row-based replication as the default replication •The default value of the  innodb_flush_method  system variable changed from  NULL  to  fsync on Unix-like systems and from  NULL  to  unbuffered  on Windows systems. This is more of a terminology and option cleanup without any tangible impact. For Unix this is just a documentation change as the default was  fsync  also in 5.7 (the default  NULL  meant  fsync ). Similarly on Windows, innodb_flush_method  default  NULL  meant  async_unbuffered  in 5.7, and is replaced by default unbuffered  in 8.0, which in combination with the existing default  innodb_use_native_aio=ON  has the same effect. • Incompatible change  The default value of the  innodb_undo_tablespaces  system variable changed from  0  to  2 . The configures the number of undo tablespaces used by InnoDB. In MySQL 8.0 the minimum value for  innodb_undo_tablespaces  is 2 and rollback segments cannot be created in the system tablespace anymore. Thus, this is a case where you cannot revert back to 5.7 behavior. The purpose of this change is to be able to auto-truncate Undo logs (see next item), reclaiming disk space used by (occasional) long transactions such as a  mysqldump . •The default value of the  innodb_undo_log_truncate  system variable changed from OFF  to  ON . When enabled, undo tablespaces that exceed the threshold value defined by innodb_max_undo_log_size  are marked for truncation. Only undo tablespaces can be truncated. Truncating undo logs that reside in the system tablespace is not supported. An upgrade from 5.7 to 8.0 automatically converts your system to use undo tablespaces, using the system tablespace is not an option in 8.0. •The default value of the  log_error_verbosity  system variable changed from  3  (Notes) to  2 (Warning). The purpose is to make the MySQL 8.0 error log less verbose by default. •The default value of the  table_open_cache  system variable changed from  2000  to  4000 . This is a minor change which increases session concurrency on table access. •The default value of the  event_scheduler  system variable changed from  OFF  to  ON . In other words, the event scheduler is enabled by default. This is an enabler for new features in SYS, for example “kill idle transactions”. •The default value of the  max_error_count  system variable changed from  64  to  1024 . This ensures that MySQL handles a larger number of warnings, such as an UPDATE statement that touches 1000s of rows and many of them give conversion warnings. It is common for many tools to batch updates, to help reduce replication lag. External tools such as pt-online-schema-change defaults to 1000, and gh- ost defaults to 100. MySQL 8.0 covers full error history for these two use cases. There are no static allocations, so this change only affects memory consumption for statements that generate lots of warnings. •The default value of the  max_allowed_packet  system variable changed from  4194304  (4M) to 67108864  (64M). The main advantage with this larger default is less chance of receiving errors about an insert or query being larger than  max_allowed_packet . It should be as big as the largest Section 11.3.4, “The BLOB and TEXT Types”  you want to use. To revert to the previous behavior, set max_allowed_packet=4194304 .