Migrating MySQL 8.0 Default Charset from latin1 to utf8mb4: A Step‑by‑Step Guide

When MySQL 8.0 changed its default character set from latin1 to utf8mb4 , many systems that previously used utf8 (limited to three‑byte characters) need to migrate to support four‑byte characters such as rare glyphs and emojis.

Migration Plan 1 (Create a New Instance)

Prepare a new MySQL instance and modify my.cnf (or my.ini ) with the following settings: [mysqld] ## Character Settings init_connect='SET NAMES utf8mb4' character-set-server = utf8mb4 collation-server = utf8mb4_general_ci skip-character-set-client-handshake ## InnoDB Settings innodb_file_format = Barracuda innodb_file_format_max = Barracuda innodb_file_per_table = 1 innodb_large_prefix = ON

Stop the application, monitor SHOW MASTER STATUS to ensure no new writes are occurring.

Export the schema: mysqldump -u -p --no-data --default-character-set=utf8mb4 --single-transaction --set-gtid-purged=OFF --databases testdb > /backup/testdb.sql

Export the data: mysqldump -u -p --no-create-info --master-data=2 --flush-logs --routines --events --triggers --default-character-set=utf8mb4 --single-transaction --set-gtid-purged=OFF --database testdb > /backup/testdata.sql

Modify the dumped DDL, replacing every occurrence of utf8 with utf8mb4 .

Import the schema: mysql -u -p testdb < /backup/testdb.sql

Import the data: mysql -u -p testdb < /backup/testdata.sql

Create the required database users in the new instance.

Change the new MySQL port, restart the service, and point the application to the new instance for testing.

Migration Plan 2 (In‑Place Conversion)

Stop the application to avoid table locks during conversion.

Shut down MySQL and back up the data directory (or perform a full logical backup).

Update the same configuration parameters shown in Plan 1 and restart MySQL.

Convert each table: ALTER TABLE t CONVERT TO CHARACTER SET utf8mb4; Note: This copies the whole table, may be slow, and locks writes.

Convert specific columns if needed (e.g., CHAR columns): ALTER TABLE t MODIFY a CHAR CHARACTER SET utf8mb4; Impact is similar to table conversion.

Convert the database itself (metadata only, fast): ALTER DATABASE sbtest CHARACTER SET utf8mb4;

Update the JDBC URL to include characterEncoding=utf8mb4 (or utf-8 as appropriate).

After migration, verify that the application reads and writes Unicode characters correctly and that no data loss occurred.

Community Announcements

The article also includes a brief notice about upcoming community activities, such as free Mycat diagnostics, a call for technical article submissions on MySQL, DBLE, and DTLE, and contact information for the open‑source community.