Before upgrading to MySQL 8.0, review the changes described in this section to identify upgrade issues that apply to your MySQL installation and applications.
Changes marked as either Known issue or Incompatible change are incompatibilities with earlier versions of MySQL, and may require your attention before you upgrade. Our aim is to avoid these changes, but occasionally they are necessary to correct problems that would be worse than an incompatibility between releases. If any upgrade issue applicable to your installation involves an incompatibility that requires special handling, follow the instructions given in the description.
MySQL Server 8.0 incorporates a global data dictionary containing information about database objects in transactional tables. In previous MySQL series, dictionary data was stored in metadata files and nontransactional system tables. As a result, the upgrade procedure is somewhat different from previous MySQL releases and requires that you verify the upgrade readiness of your installation by checking specific prerequisites. For more information, see Verifying Upgrade Prerequisites for Your MySQL 5.7 Installation. A data dictionary-enabled server entails some general operational differences; see Section 14.7, “Data Dictionary Usage Differences”.
sha256_password authentication plugins
provide more secure password encryption than the
mysql_native_password plugin, and
caching_sha2_password provides better
sha256_password. Due to
these superior security and performance characteristics of
caching_sha2_password, it is as of MySQL
8.0 the preferred authentication plugin, and is also the
default authentication plugin rather than
mysql_native_password. This change affects
both the server and the
For the server, the default value of the
default_authentication_pluginsystem variable changes from
This change applies only to new accounts created after installing or upgrading to MySQL 8.0 or higher. For accounts already existing in an upgraded installation, their authentication plugin remains unchanged. Existing users who wish to switch to
caching_sha2_passwordcan do so using the
ALTER USER user IDENTIFIED WITH caching_sha2_password BY 'password';
caching_sha2_passwordas the default authentication plugin rather than
The following sections discuss the implications of the more
prominent role of
If your MySQL installation must serve pre-8.0 clients and
you encounter compatibility issues after upgrading to MySQL
8.0 or higher, the simplest way to address those issues and
restore pre-8.0 compatibility is to reconfigure the server
to revert to the previous default authentication plugin
mysql_native_password). For example, use
these lines in the server option file:
That setting enables pre-8.0 clients to connect to 8.0
servers until such time as the clients and connectors in use
at your installation are upgraded to know about
caching_sha2_password. However, the
setting should be viewed as temporary, not as a long term or
permanent solution, because it causes new accounts created
with the setting in effect to forego the improved
authentication security provided by
The use of
more secure password hashing than
mysql_native_password (and consequent
improved client connection authentication). However, it also
has compatibility implications that may affect existing MySQL
Clients and connectors that have not been updated to know about
caching_sha2_passwordmay have trouble connecting to a MySQL 8.0 server configured with
caching_sha2_passwordas the default authentication plugin, even to use accounts that do not authenticate with
caching_sha2_password. This issue occurs because the server specifies the name of its default authentication plugin to clients. If a client or connector is based on a client/server protocol implementation that does not gracefully handle an unrecognized default authentication plugin, it may fail with an error such as one of these:
Authentication plugin 'caching_sha2_password' is not supported
Authentication plugin 'caching_sha2_password' cannot be loaded: dlopen(/usr/local/mysql/lib/plugin/caching_sha2_password.so, 2): image not found
Warning: mysqli_connect(): The server requested authentication method unknown to the client [caching_sha2_password]
For information about writing connectors to gracefully handle requests from the server for unknown default authentication plugins, see Authentication Plugin Connector-Writing Considerations.
Clients that use an account that authenticates with
caching_sha2_passwordmust use either a secure connection (made using TCP using TLS/SSL credentials, a Unix socket file, or shared memory), or an unencrypted connection that supports password exchange using an RSA key pair. This security requirement does not apply to
mysql_native_passsword, so the switch to
caching_sha2_passwordmay require additional configuration (see Section 22.214.171.124, “Caching SHA-2 Pluggable Authentication”). However, client connections in MySQL 8.0 prefer use of TLS/SSL by default, so clients that already conform to that preference may need no additional configuration.
Clients and connectors that have not been updated to know about
caching_sha2_passwordcannot connect to accounts that authenticate with
caching_sha2_passwordbecause they do not recognize this plugin as valid. (This is a particular instance of how client/server authentication plugin compatibility requirements apply, as discussed at Authentication Plugin Client/Server Compatibility.) To work around this issue, relink clients against
libmysqlclientfrom MySQL 8.0 or higher, or obtain an updated connector that recognizes
caching_sha2_passwordis also now the default authentication plugin in the
libmysqlclientclient library, authentication requires an extra round trip in the client/server protocol for connections from MySQL 8.0 clients to accounts that use
mysql_native_password(the previous default authentication plugin), unless the client program is invoked with a
libmysqlclient client library for
pre-8.0 MySQL versions is able to connect to MySQL 8.0 servers
(except for accounts that authenticate with
caching_sha2_password). That means pre-8.0
clients based on
libmysqlclient should also
be able to connect. Examples:
When an existing MySQL 8.0 installation is upgraded to MySQL
8.0.4 or higher, some older
libmysqlclient-based clients may
“automatically” upgrade if they are dynamically
linked, because they use the new client library installed by
the upgrade. For example, if the DBD::mysql driver for Perl
DBI uses dynamic linking, it can use the
libmysqlclient in place after an upgrade to
MySQL 8.0.4 or higher, with this result:
Prior to the upgrade, DBI scripts that use DBD::mysql can connect to a MySQL 8.0 server, except for accounts that authenticate with
After the upgrade, the same scripts become able to use
caching_sha2_passwordaccounts as well.
However, the preceding results occur because
libmysqlclient instances from MySQL 8.0
installations prior to 8.0.4 are binary compatible: They both
use a shared library major version number of 21. For clients
libmysqlclient from MySQL 5.7 or
older, they link to a shared library with a different version
number that is not binary compatible. In this case, the client
must be recompiled against
from 8.0.4 or higher for full compatibility with MySQL 8.0
MySQL Connector/J 5.1 through 8.0.8 is able to connect to MySQL 8.0
servers, except for accounts that authenticate with
caching_sha2_password. (Connector/J 8.0.9 or
higher is required to connect to
Clients that use an implementation of the client/server
protocol other than
libmysqlclient may need
to be upgraded to a newer version that understands the new
authentication plugin. For example, in PHP, MySQL connectivity
usually is based on
currently does not know about
caching_sha2_password. Until an updated
mysqlnd is available, the way to
enable PHP clients to connect to MySQL 8.0 is to reconfigure
the server to revert to
mysql_native_password as the default
authentication plugin, as previously discussed.
If a client or connector supports an option to explicitly
specify a default authentication plugin, use it to name a
plugin other than
Some MySQL clients support a
--default-authoption. (Standard MySQL clients such as mysql and mysqladmin support this option but can successfully connect to 8.0 servers without it. However, other clients may support a similar option. If so, it is worth trying it.)
Programs that use the
libmysqlclientC API can call the
mysql_options()function with the
MySQL Connector/Python scripts that use the native Python implementation of the client/server protocol can specify the
auth_pluginconnection option. (Alternatively, use the Connector/Python C Extension, which is able to connect to MySQL 8.0 servers without the need for
If a client or connector is available that has been updated to
caching_sha2_password, using it
is the best way to ensure compatibility when connecting to a
MySQL 8.0 server configured with
caching_sha2_password as the default
These clients and connectors have been upgraded to support
MySQL Connector/C++ 1.1.11 or higher or 8.0.7 or higher.
MySQL Connector/J 8.0.9 or higher.
MySQL Connector/NET 8.0.10 or higher (through the classic MySQL protocol).
MySQL Connector/Node.js 8.0.9 or higher.
PHP: the X DevAPI PHP extension (mysql_xdevapi) supports
PHP: the PDO_MySQL and ext/mysqli extensions do not support
caching_sha2_password. In addition, when used with PHP versions before 7.1.16 and PHP 7.2 before 7.2.4, they fail to connect with
caching_sha2_passwordis not used.
For upgrades to MySQL 8.0, the authentication plugin existing
accounts remains unchanged, including the plugin for the
'root'@'localhost' administrative account.
For new MySQL 8.0 installations, when you initialize the data
directory (using the instructions at
Section 126.96.36.199, “Initializing the Data Directory Manually Using mysqld”), the
'root'@'localhost' account is created, and
that account uses
default. To connect to the server following data directory
initialization, you must therefore use a client or connector
caching_sha2_password. If you
can do this but prefer that the
installation, install MySQL and initialize the data directory
as you normally would. Then connect to the server as
root and use
USER as follows to change the account authentication
plugin and password:
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';
If the client or connector that you use does not yet support
caching_sha2_password, you can use a
modified data directory-initialization procedure that
root account with
mysql_native_password as soon as the
account is created. To do so, use either of these techniques:
--default-authentication-plugin=mysql_native_passwordoption along with
mysql_native_passwordin an option file, and name that option file using a
--defaults-fileoption along with
--initialize-insecure. (In this case, if you continue to use that option file for subsequent server startups, new accounts will be created with
caching_sha2_passwordunless you remove the
default_authentication_pluginsetting from the option file.)
In replication scenarios for which all servers have been
upgraded to MySQL 8.0.4 or higher, slave/replica connections
to master/primary servers can use accounts that authenticate
caching_sha2_password. For such
connections, the same requirement applies as for other clients
that use accounts that authenticate with
caching_sha2_password: Use a secure
connection or RSA-based password exchange.
To connect to a
account for master/slave replication:
For MySQL built using OpenSSL, use any of the following
CHANGE MASTER TOoptions:
MASTER_SSL = 1 GET_MASTER_PUBLIC_KEY = 1 MASTER_PUBLIC_KEY_PATH='path to RSA public key file'
For MySQL built using wolfSSL, use
CHANGE MASTER TO.
Alternatively, you can use the RSA public key-related options if the required keys are supplied at server startup.
To connect to a
account for Group Replication:
For MySQL built using OpenSSL, set any of the following system variables:
SET GLOBAL group_replication_recovery_use_ssl = ON; SET GLOBAL group_replication_recovery_get_public_key = 1; SET GLOBAL group_replication_recovery_public_key_path = 'path to RSA public key file';
For MySQL built using wolfSSL, set this system variable:
SET GLOBAL group_replication_recovery_use_ssl = ON;
Alternatively, you can use the RSA public key-related options if the required keys are supplied at server startup.
Incompatible change: A MySQL storage engine is now responsible for providing its own partitioning handler, and the MySQL server no longer provides generic partitioning support.
InnoDBis the only storage engine providing a native partitioning handler that is supported in MySQL 8.0. (The
NDBstorage engine also provides native partitioning support, but it is not yet supported in MySQL 8.0.) A partitioned table using any other storage engine must be altered—either to convert it to
InnoDB, or to remove its partitioning—before upgrading the server, else it cannot be used afterwards.
For information about converting
InnoDB, see Section 188.8.131.52, “Converting Tables from MyISAM to InnoDB”.
A table creation statement that would result in a partitioned table using a storage engine without such support fails with an error (ER_CHECK_NOT_IMPLEMENTED) in MySQL 8.0. If you import databases from a dump file created in MySQL 5.7 (or earlier) using mysqldump into a MySQL 8.0 server, you must make sure that any statements creating partitioned tables do not also specify an unsupported storage engine, either by removing any references to partitioning, or by specifying the storage engine as
InnoDBor allowing it to be set as
The procedure given at Verifying Upgrade Prerequisites for Your MySQL 5.7 Installation, describes how to identify partitioned tables that must be altered before upgrading to MySQL 8.0.
See Section 22.6.2, “Partitioning Limitations Relating to Storage Engines”, for further information.
Incompatible change: Several server error codes are not used and have been removed (for a list, see Features Removed in MySQL 8.0). Applications that test specifically for any of them should be updated.
Important change: The default character set has changed from
utf8mb4. These system variables are affected:
As a result, the default character set and collation for new objects differ from previously unless an explicit character set and collation are specified. This includes databases and objects within them, such as tables, views, and stored programs. Assuming that the previous defaults were used, one way to preserve them is to start the server with these lines in the
[mysqld] character_set_server=latin1 collation_server=latin1_swedish_ci
In a replicated setting, when upgrading from MySQL 5.7 to 8.0, it is advisable to change the default character set back to the character set used in MySQL 5.7 before upgrading. After the upgrade is completed, the default character set can be changed to
Incompatible change: As of MySQL 8.0.11, it is prohibited to start the server with a
lower_case_table_namessetting that is different from the setting used when the server was initialized. The restriction is necessary because collations used by various data dictionary table fields are based on the setting defined when the server is initialized, and restarting the server with a different setting would introduce inconsistencies with respect to how identifiers are ordered and compared.
In MySQL 8.0.11, several deprecated features related to account management have been removed, such as use of the
GRANTstatement to modify nonprivilege characteristics of user accounts, the
NO_AUTO_CREATE_USERSQL mode, the
PASSWORD()function, and the
Replication from MySQL 5.7 to 8.0 of statements that refer to these removed features can cause replication failure. Applications that use any of the removed features should be revised to avoid them and use alternatives when possible, as described in Features Removed in MySQL 8.0.
To avoid a startup failure on MySQL 8.0, remove any instance of
sql_modesystem variable settings in MySQL option files.
Loading a dump file that includes the
NO_AUTO_CREATE_USERSQL mode in stored program definitions into a MySQL 8.0 server causes a failure. As of MySQL 5.7.24 and MySQL 8.0.13, mysqldump removes
NO_AUTO_CREATE_USERfrom stored program definitions. Dump files created with an earlier version of
mysqldumpmust be modified manually to remove instances of
In MySQL 8.0.11, these deprecated compatibility SQL modes were removed:
NO_TABLE_OPTIONS. They can no longer be assigned to the
sql_modesystem variable or used as permitted values for the mysqldump
Replication from MySQL 5.7 to 8.0 of statements that refer to the removed SQL modes can cause replication failure. This includes replication of
CREATEstatements for stored programs (stored procedures and functions, triggers, and events) that are executed while the current
sql_modevalue includes any of the removed modes. Applications that use any of the removed modes should be revised to avoid them.
As of MySQL 8.0.3, spatial data types permit an
SRIDattribute, to explicitly indicate the spatial reference system (SRS) for values stored in the column. See Section 11.5.1, “Spatial Data Types”.
A spatial column with an explicit
SRIDattribute is SRID-restricted: The column takes only values with that ID, and
SPATIALindexes on the column become subject to use by the optimizer. The optimizer ignores
SPATIALindexes on spatial columns with no
SRIDattribute. See Section 8.3.3, “SPATIAL Index Optimization”. If you wish the optimizer to consider
SPATIALindexes on spatial columns that are not SRID-restricted, each such column should be modified:
Verify that all values within the column have the same SRID. To determine the SRIDs contained in a geometry column
col_name, use the following query:
SELECT DISTINCT ST_SRID(col_name) FROM tbl_name;
If the query returns more than one row, the column contains a mix of SRIDs. In that case, modify its contents so all values have the same SRID.
Redefine the column to have an explicit
Several spatial functions were removed in MySQL 8.0.0 due to a spatial function namespace change that implemented an
ST_prefix for functions that perform an exact operation, or an
MBRprefix for functions that perform an operation based on minimum bounding rectangles. The use of removed spatial functions in generated column definitions could cause an upgrade failure. Before upgrading, run mysqlcheck --check-upgrade for removed spatial functions and replace any that you find with their
MBRnamed replacements. For a list of removed spatial functions, refer to Features Removed in MySQL 8.0.
Table 2.15 Renamed InnoDB Information Schema Views
Old Name New Name
After upgrading to MySQL 8.0.3 or higher, update any scripts that reference previous
The zlib library version bundled with MySQL was raised from version 1.2.3 to version 1.2.11.
compressBound()function in zlib 1.2.11 returns a slightly higher estimate of the buffer size required to compress a given length of bytes than it did in zlib version 1.2.3. The
compressBound()function is called by
InnoDBfunctions that determine the maximum row size permitted when creating compressed
InnoDBtables or inserting rows into compressed
InnoDBtables. As a result,
CREATE TABLE ... ROW_FORMAT=COMPRESSEDor
INSERToperations with row sizes very close to the maximum row size that were successful in earlier releases could now fail.
If you have compressed
InnoDBtables with large rows, it is recommended that you test compressed table
CREATE TABLEstatements on a MySQL 8.0 test instance prior to upgrading.
With the introduction of the
--innodb-directoriesfeature, the location of file-per-table and general tablespace files created with an absolute path or in a location outside of the data directory should be added to the
innodb_directoriesargument value. Otherwise,
InnoDBis not able to locate these files during recovery. To view tablespace file locations, query the
SELECT TABLESPACE_NAME, FILE_NAME FROM INFORMATION_SCHEMA.FILES \G
Undo logs no longer reside in the system tablespace in MySQL 8.0. Upgrading form MySQL 5.7 to MySQL 8.0 moves undo logs from the system tablespace (the previous default location) to separate undo tablespaces. For more information, see Section 15.7.8, “Configuring Undo Tablespaces”.
Incompatible change: As of MySQL 8.0.13, the deprecated
GROUP BYclauses have been removed. Queries that previously relied on
GROUP BYsorting may produce results that differ from previous MySQL versions. To produce a given sort order, provide an
Queries and stored program definitions from MySQL 8.0.12 or lower that use
GROUP BYclauses should be amended. Otherwise, upgrading to MySQL 8.0.13 or higher may fail, as may replicating to MySQL 8.0.13 or higher slave servers.
Some keywords may be reserved in MySQL 8.0 that were not reserved in MySQL 5.7. 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”.
After upgrading, it is recommended that you test optimizer hints specified in application code to ensure that the hints are still required to achieve the desired optimization strategy. Optimizer enhancements can sometimes render certain optimizer hints unnecessary. In some cases, an unnecessary optimizer hint may even be counterproductive.