Preparing Your Installation for Upgrade

Before upgrading to the latest MySQL 8.0 release, ensure the upgrade readiness of your current MySQL 5.7 or MySQL 8.0 server instance by performing the preliminary checks described below. The upgrade process may fail otherwise.

Tip

Consider using the MySQL Shell upgrade checker utility that enables you to verify whether MySQL server instances are ready for upgrade. You can select a target MySQL Server release to which you plan to upgrade, ranging from the MySQL Server 8.0.11 up to the MySQL Server release number that matches the current MySQL Shell release number. The upgrade checker utility carries out the automated checks that are relevant for the specified target release, and advises you of further relevant checks that you should make manually. The upgrade checker works for all GA releases of MySQL 5.7 and 8.0. Installation instructions for MySQL Shell can be found here.

Preliminary checks:

1. The following issues must not be present:
   • There must be no tables that use obsolete data types or functions.In-place upgrade to MySQL 8.0 is not supported if tables contain old temporal columns in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP columns without support for fractional seconds precision). If your tables still use the old temporal column format, upgrade them using REPAIR TABLE before attempting an in-place upgrade to MySQL 8.0. For more information, see Server Changes, in MySQL 5.7 Reference Manual.
   • There must be no orphan .frm files.
   • Triggers must not have a missing or empty definer or an invalid creation context (indicated by the character_set_client, collation_connection, Database Collation attributes displayed by SHOW TRIGGERS or the INFORMATION_SCHEMA TRIGGERS table). Any such triggers must be dumped and restored to fix the issue.To check for these issues, execute this command:

mysqlcheck -u root -p --all-databases --check-upgrade

2. If mysqlcheck reports any errors, correct the issues.
3. There must be no partitioned tables that use a storage engine that does not have native partitioning support. To identify such tables, execute this query:

SELECT TABLE_SCHEMA, TABLE_NAME

FROM INFORMATION_SCHEMA.TABLES

WHERE ENGINE NOT IN (‘innodb’, ‘ndbcluster’)

AND CREATE_OPTIONS LIKE ‘%partitioned%’;

Any table reported by the query must be altered to use InnoDB or be made nonpartitioned. To change a table storage engine to InnoDB, execute this statement:

ALTER TABLE table_name ENGINE = INNODB;

1. For information about converting MyISAM tables to InnoDB, see Section 15.6.1.5, “Converting Tables from MyISAM to InnoDB”.To make a partitioned table nonpartitioned, execute this statement:

ALTER TABLE table_name REMOVE PARTITIONING;

1. Some keywords may be reserved in MySQL 8.0 that were not reserved previously. See Section 9.3, “Keywords and Reserved Words”. This can cause words previously used as identifiers to become illegal. To fix affected statements, use identifier quoting. See Section 9.2, “Schema Object Names”.
2. There must be no tables in the MySQL 5.7 mysql system database that have the same name as a table used by the MySQL 8.0 data dictionary. To identify tables with those names, execute this query:

SELECT TABLE_SCHEMA, TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE LOWER(TABLE_SCHEMA) = ‘mysql’ and LOWER(TABLE_NAME) IN ( ‘catalogs’, ‘character_sets’, ‘check_constraints’, ‘collations’, ‘column_statistics’, ‘column_type_elements’, ‘columns’, ‘dd_properties’, ‘events’, ‘foreign_key_column_usage’, ‘foreign_keys’, ‘index_column_usage’, ‘index_partitions’, ‘index_stats’, ‘indexes’, ‘parameter_type_elements’, ‘parameters’, ‘resource_groups’, ‘routines’, ‘schemata’, ‘st_spatial_reference_systems’, ‘table_partition_values’, ‘table_partitions’, ‘table_stats’, ‘tables’, ‘tablespace_files’, ‘tablespaces’, ‘triggers’, ‘view_routine_usage’, ‘view_table_usage’ );

2. Any tables reported by the query must be dropped or renamed (use RENAME TABLE). This may also entail changes to applications that use the affected tables.
3. There must be no tables that have foreign key constraint names longer than 64 characters. Use this query to identify tables with constraint names that are too long:

SELECT TABLE_SCHEMA, TABLE_NAME

FROM INFORMATION_SCHEMA.TABLES

WHERE TABLE_NAME IN

(SELECT LEFT(SUBSTR(ID,INSTR(ID,’/’)+1), INSTR(SUBSTR(ID,INSTR(ID,’/’)+1),’_ibfk_’)-1)

FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN

WHERE LENGTH(SUBSTR(ID,INSTR(ID,’/’)+1))>64);

1. For a table with a constraint name that exceeds 64 characters, drop the constraint and add it back with constraint name that does not exceed 64 characters (use ALTER TABLE).
2. There must be no obsolete SQL modes defined by sql_mode system variable. Attempting to use an obsolete SQL mode prevents MySQL 8.0 from starting. Applications that use obsolete SQL modes should be revised to avoid them. For information about SQL modes removed in MySQL 8.0, see Server Changes.
3. There must be no views with explicitly defined columns names that exceed 64 characters (views with column names up to 255 characters were permitted in MySQL 5.7). To avoid upgrade errors, such views should be altered before upgrading. Currently, the only method of identify views with column names that exceed 64 characters is to inspect the view definition using SHOW CREATE VIEW. You can also inspect view definitions by querying the INFORMATION_SCHEMA.VIEWS table.
4. There must be no tables or stored procedures with individual ENUM or SET column elements that exceed 255 characters or 1020 bytes in length. Prior to MySQL 8.0, the maximum combined length of ENUM or SET column elements was 64K. In MySQL 8.0, the maximum character length of an individual ENUM or SET column element is 255 characters, and the maximum byte length is 1020 bytes. (The 1020 byte limit supports multibyte character sets). Before upgrading to MySQL 8.0, modify any ENUM or SET column elements that exceed the new limits. Failing to do so causes the upgrade to fail with an error.
5. Before upgrading to MySQL 8.0.13 or higher, there must be no table partitions that reside in shared InnoDB tablespaces, which include the system tablespace and general tablespaces. Identify table partitions in shared tablespaces by querying INFORMATION_SCHEMA:If upgrading from MySQL 5.7, run this query:

SELECT DISTINCT NAME, SPACE, SPACE_TYPE FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME LIKE ‘%#P#%’ AND SPACE_TYPE NOT LIKE ‘Single’;

If upgrading from an earlier MySQL 8.0 release, run this query:

SELECT DISTINCT NAME, SPACE, SPACE_TYPE FROM INFORMATION_SCHEMA.INNODB_TABLES
  WHERE NAME LIKE '%#P#%' AND SPACE_TYPE NOT LIKE 'Single';

Move table partitions from shared tablespaces to file-per-table tablespaces using ALTER TABLE ... REORGANIZE PARTITION:

ALTER TABLE table_name REORGANIZE PARTITION partition_name
  INTO (partition_definition TABLESPACE=innodb_file_per_table);

1. There must be no queries and stored program definitions from MySQL 8.0.12 or lower that use ASC or DESC qualifiers for GROUP BY clauses. Otherwise, upgrading to MySQL 8.0.13 or higher may fail, as may replicating to MySQL 8.0.13 or higher replica servers. For additional details, see SQL Changes.
2. Your MySQL 5.7 installation must not use features that are not supported by MySQL 8.0. Any changes here are necessarily installation specific, but the following example illustrates the kind of thing to look for:Some server startup options and system variables have been removed in MySQL 8.0. See Features Removed in MySQL 8.0, and Section 1.4, “Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 8.0”. If you use any of these, an upgrade requires configuration changes.Example: Because the data dictionary provides information about database objects, the server no longer checks directory names in the data directory to find databases. Consequently, the --ignore-db-dir option is extraneous and has been removed. To handle this, remove any instances of --ignore-db-dir from your startup configuration. In addition, remove or move the named data directory subdirectories before upgrading to MySQL 8.0. (Alternatively, let the 8.0 server add those directories to the data dictionary as databases, then remove each of those databases using DROP DATABASE.)
3. If you intend to change the lower_case_table_names setting to 1 at upgrade time, ensure that schema and table names are lowercase before upgrading. Otherwise, a failure could occur due to a schema or table name lettercase mismatch. You can use the following queries to check for schema and table names containing uppercase characters:

mysql> select TABLE_NAME, if(sha(TABLE_NAME) !=sha(lower(TABLE_NAME)),'Yes','No') as UpperCase from information_schema.tables;

As of MySQL 8.0.19, if lower_case_table_names=1, table and schema names are checked by the upgrade process to ensure that all characters are lowercase. If table or schema names are found to contain uppercase characters, the upgrade process fails with an error.

Note

Changing the lower_case_table_names setting at upgrade time is not recommended.

If upgrade to MySQL 8.0 fails due to any of the issues outlined above, the server reverts all changes to the data directory. In this case, remove all redo log files and restart the MySQL 5.7 server on the existing data directory to address the errors. The redo log files (ib_logfile*) reside in the MySQL data directory by default. After the errors are fixed, perform a slow shutdown (by setting innodb_fast_shutdown=0) before attempting the upgrade again.

source : https://dev.mysql.com/doc/refman/8.0/en/upgrade-prerequisites.html