Changes in MySQL 8.0 •The default value of the  expire_logs_days  system variable changed from  0  to  30 . The new default 30  causes  mysqld  to periodically purge unused binary logs that are older than 30 days. This change helps prevent excessive amounts of disk space being wasted on binary logs that are no longer needed for replication or recovery purposes. The old value of  0  disables any automatic binary log purges. •The default value of the  master_info_repository  and  relay_log_info_repository  system variables change from  FILE  to  TABLE . Thus in 8.0, replication metadata is stored in InnoDB by default. This increases reliability to try and achieve crash safe replication by default. •The default value of the  transaction-write-set-extraction  system variable changed from  OFF to  XXHASH64 . This change enables transaction write sets by default. By using Transaction Write Sets, the source has to do slightly more work to generate the write sets, but the result is helpful in conflict detection. This is a requirement for Group Replication and the new default makes it easy to enable binary log writeset parallelization on the source to speed up replication. •The default value of the  slave_rows_search_algorithms  system variable changed from INDEX_SCAN,TABLE_SCAN  to  INDEX_SCAN,HASH_SCAN . This change speeds up row-based replication by reducing the number of table scans the replica applier has to do to apply the changes to a table without a primary key. •The default value of the  slave_pending_jobs_size_max  system variable changed from  16M  to 128M . This change increases the amount of memory available to multithreaded replicas. •The default value of the  gtid_executed_compression_period  system variable changed from  1000 to  0 . This change ensures that compression of the  mysql.gtid_executed  table only occurs implicitly as required. •The default value of  group_replication_autorejoin_tries  changed from 0 to 3, which means that automatic rejoin is enabled by default. This system variable specifies the number of tries that a member makes to automatically rejoin the group if it is expelled, or if it is unable to contact a majority of the group before the  group_replication_unreachable_majority_timeout  setting is reached. •The default value of  group_replication_exit_state_action  changed from  ABORT_SERVER  to READ_ONLY . This means that when a member exits the group, for example after a network failure, the instance becomes read-only, rather than being shut down. •The default value of  group_replication_member_expel_timeout  changed from 0 to 5, meaning that a member suspected of having lost contact with the group is liable for expulsion 5 seconds after the 5-second detection period. 282 Most of these defaults are reasonably good for both development and production environments. There is one exception to this, we decided to keep the new option called innodb_dedicated_server  set to  OFF although we recommend it to be  ON  for production environments. The reason for defaulting to  OFF  is that it causes shared environments such as developer laptops to become unusable, because it takes  all  the memory it can find. For production environments we recommend setting  innodb_dedicated_server  to  ON . When set to  ON  the following InnoDB variables (if not specified explicitly) are autoscaled based on the available memory  innodb_buffer_pool_size ,  innodb_log_file_size , and  innodb_flush_method . See Section 15.8.12, “Enabling Automatic Configuration for a Dedicated MySQL Server” . Although the new defaults are the best configuration choices for most use cases, there are special cases, as well as legacy reasons for using existing 5.7 configuration choices. For example, some people prefer to upgrade to 8.0 with as few changes to their applications or operational environment as possible. We recommend to evaluate all the new defaults and use as many as you can. Most new defaults can be tested in 5.7, so you can validate the new defaults in 5.7 production before upgrading to 8.0. For the few defaults Group Replication Defaults