Before upgrading to MySQL 8.0, review the changes described in this section to identify those that apply to your current MySQL installation and applications. Perform any recommended actions.
Changes marked as Incompatible change are incompatibilities with earlier versions of MySQL, and may require your attention before upgrading. 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 an upgrade issue applicable to your installation involves an incompatibility, 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 requires that you verify the upgrade readiness of your installation by checking specific prerequisites. For more information, see Section 3.6, “Preparing Your Installation for Upgrade”. A data dictionary-enabled server entails some general operational differences; see Section 16.7, “Data Dictionary Usage Differences”.
The caching_sha2_password
and
sha256_password
authentication plugins
provide more secure password encryption than the
mysql_native_password
plugin, and
caching_sha2_password
provides better
performance than 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 libmysqlclient
client
library:
For the server, the default value of the
default_authentication_plugin
system variable changes frommysql_native_password
tocaching_sha2_password
.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_password
can do so using theALTER USER
statement:ALTER USER user IDENTIFIED WITH caching_sha2_password BY 'password';
The
libmysqlclient
library treatscaching_sha2_password
as the default authentication plugin rather thanmysql_native_password
.
The following sections discuss the implications of the more
prominent role of caching_sha2_password
:
caching_sha2_password Compatibility Issues and Solutions
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:
[mysqld]
default_authentication_plugin=mysql_native_password
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 caching_sha2_password
.
The use of caching_sha2_password
offers 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
installations:
Clients and connectors that have not been updated to know about
caching_sha2_password
may have trouble connecting to a MySQL 8.0 server configured withcaching_sha2_password
as the default authentication plugin, even to use accounts that do not authenticate withcaching_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_password
must 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 tomysql_native_passsword
, so the switch tocaching_sha2_password
may require additional configuration (see Section 8.4.1.2, “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_password
cannot connect to accounts that authenticate withcaching_sha2_password
because 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 againstlibmysqlclient
from MySQL 8.0 or higher, or obtain an updated connector that recognizescaching_sha2_password
.Because
caching_sha2_password
is also now the default authentication plugin in thelibmysqlclient
client library, authentication requires an extra round trip in the client/server protocol for connections from MySQL 8.0 clients to accounts that usemysql_native_password
(the previous default authentication plugin), unless the client program is invoked with a--default-auth=mysql_native_password
option.
The 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:
Standard MySQL clients such as mysql and mysqladmin are
libmysqlclient
-based.The DBD::mysql driver for Perl DBI is
libmysqlclient
-based.MySQL Connector/Python has a C Extension module that is
libmysqlclient
-based. To use it, include theuse_pure=False
option at connect time.
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
caching_sha2_password
.After the upgrade, the same scripts become able to use
caching_sha2_password
accounts 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
linked to 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 libmysqlclient
from 8.0.4 or higher for full compatibility with MySQL 8.0
servers and caching_sha2_password
accounts.
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
caching_sha2_password
accounts.)
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 mysqlnd
, which currently
does not know about caching_sha2_password
.
Until an updated version of 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 caching_sha2_password
. Examples:
Some MySQL clients support a
--default-auth
option. (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
libmysqlclient
C API can call themysql_options()
function with theMYSQL_DEFAULT_AUTH
option.MySQL Connector/Python scripts that use the native Python implementation of the client/server protocol can specify the
auth_plugin
connection option. (Alternatively, use the Connector/Python C Extension, which is able to connect to MySQL 8.0 servers without the need forauth_plugin
.)
caching_sha2_password-Compatible Clients and Connectors
If a client or connector is available that has been updated to
know about 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
authentication plugin.
These clients and connectors have been upgraded to support
caching_sha2_password
:
The
libmysqlclient
client library in MySQL 8.0 (8.0.4 or higher). Standard MySQL clients such as mysql and mysqladmin arelibmysqlclient
-based, so they are compatible as well.The
libmysqlclient
client library in MySQL 5.7 (5.7.23 or higher). Standard MySQL clients such as mysql and mysqladmin arelibmysqlclient
-based, so they are compatible as well.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
caching_sha2_password
.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 withdefault_authentication_plugin=caching_sha2_password
even ifcaching_sha2_password
is not used.
caching_sha2_password and the root Administrative Account
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 2.9.1, “Initializing the Data Directory”), the
'root'@'localhost'
account is created, and
that account uses caching_sha2_password
by
default. To connect to the server following data directory
initialization, you must therefore use a client or connector
that supports caching_sha2_password
. If you
can do this but prefer that the root
account
use mysql_native_password
after installation,
install MySQL and initialize the data directory as you normally
would. Then connect to the server as root
and
use ALTER 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 associates the
root
account with
mysql_native_password
as soon as the account
is created. To do so, use either of these techniques:
Supply a
--default-authentication-plugin=mysql_native_password
option along with--initialize
or--initialize-insecure
.Set
default_authentication_plugin
tomysql_native_password
in an option file, and name that option file using a--defaults-file
option along with--initialize
or--initialize-insecure
. (In this case, if you continue to use that option file for subsequent server startups, new accounts are created withmysql_native_password
rather thancaching_sha2_password
unless you remove thedefault_authentication_plugin
setting from the option file.)
caching_sha2_password and Replication
In replication scenarios for which all servers have been
upgraded to MySQL 8.0.4 or higher, replica connections to source
servers can use accounts that authenticate with
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 caching_sha2_password
account
for source/replica replication:
Use any of the following
CHANGE MASTER TO
options:MASTER_SSL = 1 GET_MASTER_PUBLIC_KEY = 1 MASTER_PUBLIC_KEY_PATH='path to RSA public key file'
Alternatively, you can use the RSA public key-related options if the required keys are supplied at server startup.
To connect to a caching_sha2_password
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';
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.
InnoDB
andNDB
are the only storage engines that provide a native partitioning handler that is supported in MySQL 8.0. A partitioned table using any other storage engine must be altered—either to convert it toInnoDB
orNDB
, or to remove its partitioning—before upgrading the server, else it cannot be used afterwards.For information about converting
MyISAM
tables toInnoDB
, see Section 17.6.1.5, “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
InnoDB
or allowing it to be set asInnoDB
by default.NoteThe procedure given at Section 3.6, “Preparing Your Installation for Upgrade”, describes how to identify partitioned tables that must be altered before upgrading to MySQL 8.0.
See Section 26.6.2, “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
latin1
toutf8mb4
. These system variables are affected:The default value of the
character_set_server
andcharacter_set_database
system variables has changed fromlatin1
toutf8mb4
.The default value of the
collation_server
andcollation_database
system variables has changed fromlatin1_swedish_ci
toutf8mb4_0900_ai_ci
.
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
my.cnf
file:[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
utf8mb4
.In addition, you should be aware that MySQL 8.0 enforces checks on permitted characters in a given character set which MySQL 5.7 does not; this is a known issue. This means that, prior to attempting to upgrade, you should ensure that no comments contain characters that are not defined for the character set in use. You can fix this in either of two ways:
Change the character set to one that includes the character or characters in question.
Remove the offending character or characters.
The preceding applies to table, file, and index comments.
Incompatible change: As of MySQL 8.0.11, it is prohibited to start the server with a
lower_case_table_names
setting 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 thelower_case_table_names
setting that was defined when the server was 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
GRANT
statement to modify nonprivilege characteristics of user accounts, theNO_AUTO_CREATE_USER
SQL mode, thePASSWORD()
function, and theold_passwords
system variable.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
NO_AUTO_CREATE_USER
fromsql_mode
system variable settings in MySQL option files.Loading a dump file that includes the
NO_AUTO_CREATE_USER
SQL 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 removesNO_AUTO_CREATE_USER
from stored program definitions. Dump files created with an earlier version ofmysqldump
must be modified manually to remove instances ofNO_AUTO_CREATE_USER
.In MySQL 8.0.11, these deprecated compatibility SQL modes were removed:
DB2
,MAXDB
,MSSQL
,MYSQL323
,MYSQL40
,ORACLE
,POSTGRESQL
,NO_FIELD_OPTIONS
,NO_KEY_OPTIONS
,NO_TABLE_OPTIONS
. They can no longer be assigned to thesql_mode
system variable or used as permitted values for the mysqldump--compatible
option.Removal of
MAXDB
means that theTIMESTAMP
data type forCREATE TABLE
orALTER TABLE
is no longer treated asDATETIME
.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
CREATE
statements for stored programs (stored procedures and functions, triggers, and events) that are executed while the currentsql_mode
value includes any of the removed modes. Applications that use any of the removed modes should be revised to avoid them.The text of many MySQL 8.0 error messages has been revised and improved to provide more and better information than in MySQL 5.7. If your application depends on specific content or formatting of error messages, you should test these and be prepared to update the application accordingly prior to performing an upgrade.
As of MySQL 8.0.3, spatial data types permit an
SRID
attribute, to explicitly indicate the spatial reference system (SRS) for values stored in the column. See Section 13.4.1, “Spatial Data Types”.A spatial column with an explicit
SRID
attribute is SRID-restricted: The column takes only values with that ID, andSPATIAL
indexes on the column become subject to use by the optimizer. The optimizer ignoresSPATIAL
indexes on spatial columns with noSRID
attribute. See Section 10.3.3, “SPATIAL Index Optimization”. If you want the optimizer to considerSPATIAL
indexes 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
SRID
attribute.Recreate the
SPATIAL
index.
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 anMBR
prefix 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 theirST_
orMBR
named replacements. For a list of removed spatial functions, refer to Features Removed in MySQL 8.0.The
BACKUP_ADMIN
privilege is automatically granted to users with theRELOAD
privilege when performing an in-place upgrade to MySQL 8.0.3 or higher.From MySQL 8.0.13, because of differences between row-based or mixed replication mode and statement-based replication mode in the way that temporary tables are handled, there are new restrictions on switching the binary logging format at runtime.
SET @@SESSION.binlog_format
cannot be used if the session has any open temporary tables.SET @@global.binlog_format
andSET @@persist.binlog_format
cannot be used if any replication channel has any open temporary tables.SET @@persist_only.binlog_format
is allowed if replication channels have open temporary tables, because unlikePERSIST
,PERSIST_ONLY
does not modify the runtime global system variable value.SET @@global.binlog_format
andSET @@persist.binlog_format
cannot be used if any replication channel applier is running. This is because the change only takes effect on a replication channel when its applier is restarted, at which time the replication channel might have open temporary tables. This behavior is more restrictive than before.SET @@persist_only.binlog_format
is allowed if any replication channel applier is running.From MySQL 8.0.27, configuring a session setting for
internal_tmp_mem_storage_engine
requires theSESSION_VARIABLES_ADMIN
orSYSTEM_VARIABLES_ADMIN
privilege.As of MySQL 8.0.27, the clone plugin permits concurrent DDL operations on the donor MySQL Server instance while a cloning operation is in progress. Previously, a backup lock was held during the cloning operation, preventing concurrent DDL on the donor. To revert to the previous behavior of blocking concurrent DDL on the donor during a clone operation, enable the
clone_block_ddl
variable. See Section 7.6.7.4, “Cloning and Concurrent DDL”.
From MySQL 8.0.30, error log components listed in the
log_error_services
value at startup are loaded implicitly early in the MySQL Server startup sequence. If you have previously installed loadable error log components usingINSTALL COMPONENT
and you list those components in alog_error_services
setting that is read at startup (from an option file, for example), your configuration should be updated to avoid startup warnings. For more information, see Error Log Configuration Methods.
INFORMATION_SCHEMA
views based onInnoDB
system tables were replaced by internal system views on data dictionary tables. AffectedInnoDB
INFORMATION_SCHEMA
views were renamed:Table 3.1 Renamed InnoDB Information Schema Views
Old Name New Name INNODB_SYS_COLUMNS
INNODB_COLUMNS
INNODB_SYS_DATAFILES
INNODB_DATAFILES
INNODB_SYS_FIELDS
INNODB_FIELDS
INNODB_SYS_FOREIGN
INNODB_FOREIGN
INNODB_SYS_FOREIGN_COLS
INNODB_FOREIGN_COLS
INNODB_SYS_INDEXES
INNODB_INDEXES
INNODB_SYS_TABLES
INNODB_TABLES
INNODB_SYS_TABLESPACES
INNODB_TABLESPACES
INNODB_SYS_TABLESTATS
INNODB_TABLESTATS
INNODB_SYS_VIRTUAL
INNODB_VIRTUAL
After upgrading to MySQL 8.0.3 or higher, update any scripts that reference previous
InnoDB
INFORMATION_SCHEMA
view names.The zlib library version bundled with MySQL was raised from version 1.2.3 to version 1.2.11.
The zlib
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. ThecompressBound()
function is called byInnoDB
functions that determine the maximum row size permitted when creating compressedInnoDB
tables or inserting and updating rows in compressedInnoDB
tables. As a result,CREATE TABLE ... ROW_FORMAT=COMPRESSED
,INSERT
, andUPDATE
operations with row sizes very close to the maximum row size that were successful in earlier releases could now fail. To avoid this issue, testCREATE TABLE
statements for compressedInnoDB
tables with large rows on a MySQL 8.0 test instance prior to upgrading.With the introduction of the
--innodb-directories
feature, 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 theinnodb_directories
argument value. Otherwise,InnoDB
is not able to locate these files during recovery. To view tablespace file locations, query the Information SchemaFILES
table:SELECT TABLESPACE_NAME, FILE_NAME FROM INFORMATION_SCHEMA.FILES \G
Undo logs can no longer reside in the system tablespace. In MySQL 8.0, undo logs reside in two undo tablespaces by default. For more information, see Section 17.6.3.4, “Undo Tablespaces”.
When upgrading from MySQL 5.7 to MySQL 8.0, any undo tablespaces that exist in the MySQL 5.7 instance are removed and replaced by two new default undo tablespaces. Default undo tablespaces are created in the location defined by the
innodb_undo_directory
variable. If theinnodb_undo_directory
variable is undefined, undo tablespaces are created in the data directory. Upgrade from MySQL 5.7 to MySQL 8.0 requires a slow shutdown which ensures that undo tablespaces in the MySQL 5.7 instance are empty, permitting them to be removed safely.When upgrading to MySQL 8.0.14 or later from an earlier MySQL 8.0 release, undo tablespaces that exist in the pre-upgrade instance as a result of an
innodb_undo_tablespaces
setting greater than 2 are treated as user-defined undo tablespaces, which can be deactivated and dropped usingALTER UNDO TABLESPACE
andDROP UNDO TABLESPACE
syntax, respectively, after upgrading. Upgrade within the MySQL 8.0 release series may not always require a slow shutdown which means that existing undo tablespaces could contain undo logs. Therefore, existing undo tablespaces are not removed by the upgrade process.Incompatible change: As of MySQL 8.0.17, the
CREATE TABLESPACE ... ADD DATAFILE
clause does not permit circular directory references. For example, the circular directory reference (/../
) in the following statement is not permitted:CREATE TABLESPACE ts1 ADD DATAFILE ts1.ibd 'any_directory/../ts1.ibd';
An exception to the restriction exists on Linux, where a circular directory reference is permitted if the preceding directory is a symbolic link. For example, the data file path in the example above is permitted if
any_directory
is a symbolic link. (It is still permitted for data file paths to begin with '../
'.)To avoid upgrade issues, remove any circular directory references from tablespace data file paths before upgrading to MySQL 8.0.17 or higher. To inspect tablespace paths, query the Information Schema
INNODB_DATAFILES
table.Due to a regression introduced in MySQL 8.0.14, in-place upgrade on a case-sensitive file system from MySQL 5.7 or a MySQL 8.0 release prior to MySQL 8.0.14 to MySQL 8.0.16 failed for instances with partitioned tables and
lower_case_table_names=1
. The failure was caused by a case mismatch issue related to partitioned table file names. The fix that introduced the regression was reverted, which permits upgrades to MySQL 8.0.17 from MySQL 5.7 or MySQL 8.0 releases prior to MySQL 8.0.14 to function as normal. However, the regression is still present in the MySQL 8.0.14, 8.0.15, and 8.0.16 releases.In-place upgrade on a case-sensitive file system from MySQL 8.0.14, 8.0.15, or 8.0.16 to MySQL 8.0.17 fails with the following error when starting the server after upgrading binaries or packages to MySQL 8.0.17 if partitioned tables are present and
lower_case_table_names=1
:Upgrading from server version version_number with partitioned tables and lower_case_table_names == 1 on a case sensitive file system may cause issues, and is therefore prohibited. To upgrade anyway, restart the new server version with the command line option 'upgrade=FORCE'. When upgrade is completed, please execute 'RENAME TABLE part_table_name TO new_table_name; RENAME TABLE new_table_name TO part_table_name;' for each of the partitioned tables. Please see the documentation for further information.
If you encounter this error when upgrading to MySQL 8.0.17, perform the following workaround:
Restart the server with
--upgrade=force
to force the upgrade operation to proceed.Identify partitioned table file names with lowercase partition name delimiters
(#p#
or#sp#
):mysql> SELECT FILE_NAME FROM INFORMATION_SCHEMA.FILES WHERE FILE_NAME LIKE '%#p#%' OR FILE_NAME LIKE '%#sp#%';
For each file identified, rename the associated table using a temporary name, then rename the table back to its original name.
mysql> RENAME TABLE table_name TO temporary_table_name; mysql> RENAME TABLE temporary_table_name TO table_name;
Verify that there are no partitioned table file names lowercase partition name delimiters (an empty result set should be returned).
mysql> SELECT FILE_NAME FROM INFORMATION_SCHEMA.FILES WHERE FILE_NAME LIKE '%#p#%' OR FILE_NAME LIKE '%#sp#%'; Empty set (0.00 sec)
Run
ANALYZE TABLE
on each renamed table to update the optimizer statistics in themysql.innodb_index_stats
andmysql.innodb_table_stats
tables.
Because of the regression still present in the MySQL 8.0.14, 8.0.15, and 8.0.16 releases, importing partitioned tables from MySQL 8.0.14, 8.0.15, or 8.0.16 to MySQL 8.0.17 is not supported on case-sensitive file systems where
lower_case_table_names=1
. Attempting to do so results in a “Tablespace is missing for table” error.MySQL uses delimiter strings when constructing tablespace names and file names for table partitions. A “
#p#
” delimiter string precedes partition names, and an “#sp#
” delimiter string precedes subpartition names, as shown:schema_name.table_name#p#partition_name#sp#subpartition_name table_name#p#partition_name#sp#subpartition_name.ibd
Historically, delimiter strings have been uppercase (
#P#
and#SP#
) on case-sensitive file systems such as Linux, and lowercase (#p#
and#sp#
) on case-insensitive file systems such as Windows. As of MySQL 8.0.19, delimiter strings are lowercase on all file systems. This change prevents issues when migrating data directories between case-sensitive and case-insensitive file systems. Uppercase delimiter strings are no longer used.Additionally, partition tablespace names and file names generated based on user-specified partition or subpartition names, which can be specified in uppercase or lowercase, are now generated (and stored internally) in lowercase regardless of the
lower_case_table_names
setting to ensure case-insensitivity. For example, if a table partition is created with the namePART_1
, the tablespace name and file name are generated in lowercase:schema_name.table_name#p#part_1 table_name#p#part_1.ibd
During upgrade, MySQL checks and modifies if necessary:
Partition file names on disk and in the data dictionary to ensure lowercase delimiters and partition names.
Partition metadata in the data dictionary for related issues introduced by previous bug fixes.
InnoDB
statistics data for related issues introduced by previous bug fixes.
During tablespace import operations, partition tablespace file names on disk are checked and modified if necessary to ensure lowercase delimiters and partition names.
As of MySQL 8.0.21, a warning is written to the error log at startup or when upgrading from MySQL 5.7 if tablespace data files are found to reside in unknown directories. Known directories are those defined by the
datadir
,innodb_data_home_dir
, andinnodb_directories
variables. To make a directory known, add it to theinnodb_directories
setting. Making directories known ensures that data files can be found during recovery. For more information, see Tablespace Discovery During Crash Recovery.Important change: From MySQL 8.0.30, the
innodb_redo_log_capacity
variable controls the amount of disk space occupied by redo log files. With this change, the default number of redo log files and their location has also changed. From MySQL 8.0.30,InnoDB
maintains 32 redo log files in the#innodb_redo
directory in the data directory. Previously,InnoDB
created two redo log files in the data directory by default, and the number and size of redo log files were controlled by theinnodb_log_files_in_group
andinnodb_log_file_size
variables. These two variables are now deprecated.When the
innodb_redo_log_capacity
setting is defined,innodb_log_files_in_group
andinnodb_log_file_size
settings are ignored; otherwise, those settings are used to compute theinnodb_redo_log_capacity
setting (innodb_log_files_in_group
*innodb_log_file_size
=innodb_redo_log_capacity
). If none of those variables are set, redo log capacity is set to theinnodb_redo_log_capacity
default value, which is 104857600 bytes (100MB).As is generally required for any upgrade, this change requires a clean shutdown before upgrading.
For more information about this feature, see Section 17.6.5, “Redo Log”.
Before MySQL 5.7.35, there was no size limitation for indexes in tables with redundant or compact row format. As of MySQL 5.7.35, the limit is 767 bytes. An upgrade from a MySQL version before 5.7.35 to MySQL 8.0 can produce inaccessible tables. If a table with redundant or compact row format has an index larger than 767 bytes, drop the index and re-create it before an upgrade to MySQL 8.0. The error message is:
mysql> ERROR 1709 (HY000): Index column size too large. The maximum column size is 767 bytes.
Incompatible change: As of MySQL 8.0.13, the deprecated
ASC
orDESC
qualifiers forGROUP BY
clauses have been removed. Queries that previously relied onGROUP BY
sorting may produce results that differ from previous MySQL versions. To produce a given sort order, provide anORDER BY
clause.Queries and stored program definitions from MySQL 8.0.12 or lower that use
ASC
orDESC
qualifiers forGROUP BY
clauses should be amended. Otherwise, upgrading to MySQL 8.0.13 or higher may fail, as may replicating to MySQL 8.0.13 or higher replica servers.Some keywords may be reserved in MySQL 8.0 that were not reserved in MySQL 5.7. See Section 11.3, “Keywords and Reserved Words”. This can cause words previously used as identifiers to become illegal. To fix affected statements, use identifier quoting. See Section 11.2, “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.
Incompatible change: In MySQL 5.7, specifying a
FOREIGN KEY
definition for anInnoDB
table without aCONSTRAINT
clause, or specifying thesymbol
CONSTRAINT
keyword without asymbol
, causesInnoDB
to use a generated constraint name. That behavior changed in MySQL 8.0, withInnoDB
using theFOREIGN KEY
value instead of a generated name. Because constraint names must be unique per schema (database), the change caused errors due to foreign key index names that were not unique per schema. To avoid such errors, the new constraint naming behavior has been reverted in MySQL 8.0.16, andindex_name
InnoDB
once again uses a generated constraint name.For consistency with
InnoDB
,NDB
releases based on MySQL 8.0.16 or higher use a generated constraint name if theCONSTRAINT
clause is not specified, or thesymbol
CONSTRAINT
keyword is specified without asymbol
.NDB
releases based on MySQL 5.7 and earlier MySQL 8.0 releases used theFOREIGN KEY
value.index_name
The changes described above may introduce incompatibilities for applications that depend on the previous foreign key constraint naming behavior.
The handling of system variable values by MySQL flow control functions such as
IFNULL()
andCASE()
changed in MySQL 8.0.22; system variable values are now handled as column values of the same character and collation, rather than as constants. Some queries using these functions with system variables that were previously successful may subsequently be rejected with Illegal mix of collations. In such cases, cast the system variable to the correct character set and collation.Incompatible change: MySQL 8.0.28 fixes an issue in previous MySQL 8.0 releases whereby the
CONVERT()
function sometimes allowed invalid casts ofBINARY
values to nonbinary character sets. Applications which may have relied on this behavior should be checked and if necessary modified prior to upgrade.In particular, where
CONVERT()
was used as part of an expression for an indexed generated column, the change in the function's behavior may result in index corruption following an upgrade to MySQL 8.0.28. You can prevent this from happening by following these steps:Prior to performing the upgrade, correct any invalid input data.
Drop and then re-create the index.
You can also force a table rebuild using
ALTER TABLE
, instead.table
FORCEUpgrade the MySQL software.
If you cannot validate the input data beforehand, you should not re-create the index or rebuild the table until after you perform the upgrade to MySQL 8.0.28.
MySQL 8.0 comes with improved defaults, aiming at the best out of the box experience possible. These changes are driven by the fact that technology is advancing (machines have more CPUS, use SSDs and so on), more data is being stored, MySQL is evolving (InnoDB, Group Replication, AdminAPI), and so on. The following table summarizes the defaults which have been changed to provide the best MySQL experience for the majority of users.
Option/Parameter | Old Default | New Default |
---|---|---|
Server changes | ||
character_set_server |
latin1 | utf8mb4 |
collation_server |
latin1_swedish_ci | utf8mb4_0900_ai_ci |
explicit_defaults_for_timestamp |
OFF | ON |
optimizer_trace_max_mem_size |
16KB | 1MB |
validate_password_check_user_name |
OFF | ON |
back_log |
-1 (autosize) changed from : back_log = 50 + (max_connections / 5) | -1 (autosize) changed to : back_log = max_connections |
max_allowed_packet |
4194304 (4MB) | 67108864 (64MB) |
max_error_count |
64 | 1024 |
event_scheduler |
OFF | ON |
table_open_cache |
2000 | 4000 |
log_error_verbosity |
3 (Notes) | 2 (Warning) |
local_infile |
ON (5.7) | OFF |
InnoDB changes | ||
innodb_undo_tablespaces |
0 | 2 |
innodb_undo_log_truncate |
OFF | ON |
innodb_flush_method |
NULL | fsync (Unix), unbuffered (Windows) |
innodb_autoinc_lock_mode |
1 (consecutive) | 2 (interleaved) |
innodb_flush_neighbors |
1 (enable) | 0 (disable) |
innodb_max_dirty_pages_pct_lwm |
0 (%) | 10 (%) |
innodb_max_dirty_pages_pct |
75 (%) | 90 (%) |
Performance Schema changes | ||
performance-schema-instrument='wait/lock/metadata/sql/%=ON' |
OFF | ON |
performance-schema-instrument='memory/%=COUNTED' |
OFF | COUNTED |
performance-schema-consumer-events-transactions-current=ON |
OFF | ON |
performance-schema-consumer-events-transactions-history=ON |
OFF | ON |
performance-schema-instrument='transaction%=ON' |
OFF | ON |
Replication changes | ||
log_bin |
OFF | ON |
server_id |
0 | 1 |
log-slave-updates |
OFF | ON |
expire_logs_days |
0 | 30 |
master-info-repository |
FILE | TABLE |
relay-log-info-repository |
FILE | TABLE |
transaction-write-set-extraction |
OFF | XXHASH64 |
slave_rows_search_algorithms |
INDEX_SCAN, TABLE_SCAN | INDEX_SCAN, HASH_SCAN |
slave_pending_jobs_size_max |
16M | 128M |
gtid_executed_compression_period |
1000 | 0 |
Group Replication changes | ||
group_replication_autorejoin_tries |
0 | 3 |
group_replication_exit_state_action |
ABORT_SERVER | READ_ONLY |
group_replication_member_expel_timeout |
0 | 5 |
For more information about options or variables which have been added, see Option and Variable Changes for MySQL 8.0, in the MySQL Server Version Reference.
The following sections explain the changes to defaults and any impact they might have on your deployment.
Server Defaults
The default value of the
character_set_server
system variable and command line option--character-set-server
changed fromlatin1
toutf8mb4
. This is the server’s default character set. At this time, UTF8MB4 is the dominant character encoding for the web, and this change makes life easier for the vast majority of MySQL users. The upgrade from 5.7 to 8.0 does not change the character set for any existing database objects, but, unless you setcharacter_set_server
explicitly (either back to the previous value, or to a new one), a new schema usesutf8mb4
by default. We recommend that you move toutf8mb4
whenever possible.The default value of the
collation_server
system variable and command line argument--collation-server
changed fromlatin1_swedish_ci
toutf8mb4_0900_ai_ci
. This is the server’s default collation, the ordering of characters in a character set. There is a link between collations and character sets as each character set comes with a list of possible collations. The upgrade from 5.7 to 8.0 does not change any collation for any existing database objects, but takes effect for new objects.The default value of the
explicit_defaults_for_timestamp
system variable changed fromOFF
(MySQL legacy behavior) toON
(SQL standard behavior). This option was originally introduced in 5.6 and wasOFF
in 5.6 and 5.7.The default value of the
optimizer_trace_max_mem_size
system variable changed from16KB
to1MB
. The old default caused the optimizer trace to be truncated for any non-trivial query. This change ensures useful optimizer traces for most queries.The default value of the
validate_password_check_user_name
system variable changed fromOFF
toON
. This means that when thevalidate_password
plugin is enabled, by default it now rejects passwords that match the current session user name.The autosize algorithm for the
back_log
system variable has changed. The value for autosize (-1) is now set to the value ofmax_connections
, which is bigger than the calculated by50 + (max_connections / 5)
. Theback_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, withmax_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.The default value of the
max_allowed_packet
system variable changed from4194304
(4M) to67108864
(64M). The main advantage with this larger default is less chance of receiving errors about an insert or query being larger thanmax_allowed_packet
. It should be as big as the largest Section 13.3.4, “The BLOB and TEXT Types” you want to use. To revert to the previous behavior, setmax_allowed_packet=4194304
.The default value of the
max_error_count
system variable changed from64
to1024
. 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
event_scheduler
system variable changed fromOFF
toON
. 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
table_open_cache
system variable changed from2000
to4000
. This is a minor change which increases session concurrency on table access.The default value of the
log_error_verbosity
system variable changed from3
(Notes) to2
(Warning). The purpose is to make the MySQL 8.0 error log less verbose by default.
InnoDB Defaults
Incompatible change The default value of the
innodb_undo_tablespaces
system variable changed from0
to2
. The configures the number of undo tablespaces used by InnoDB. In MySQL 8.0 the minimum value forinnodb_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 fromOFF
toON
. When enabled, undo tablespaces that exceed the threshold value defined byinnodb_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
innodb_flush_method
system variable changed fromNULL
tofsync
on Unix-like systems and fromNULL
tounbuffered
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 wasfsync
also in 5.7 (the defaultNULL
meantfsync
). Similarly on Windows,innodb_flush_method
defaultNULL
meantasync_unbuffered
in 5.7, and is replaced by defaultunbuffered
in 8.0, which in combination with the existing defaultinnodb_use_native_aio=ON
has the same effect.Incompatible change The default value of the
innodb_autoinc_lock_mode
system variable changed from1
(consecutive) to2
(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 type, which occurred in MySQL 5.7. Statement-based replication requires the consecutive auto-increment lock mode to ensure that auto-increment values are assigned in a predictable and repeatable order for a given sequence of SQL statements, whereas row-based replication is not sensitive to the execution order of SQL statements. Thus, this change is known to be incompatible with statement based replication, and may break some applications or user-generated test suites that depend on sequential auto increment. The previous default can be restored by settinginnodb_autoinc_lock_mode=1;
The default value of the
innodb_flush_neighbors
system variable changes from1
(enable) to0
(disable). This is done because fast IO (SSDs) is now the default for deployment. We expect that for the majority of users, this results in a small performance gain. Users who are using slower hard drives may see a performance loss, and are encouraged to revert to the previous defaults by settinginnodb_flush_neighbors=1
.The default value of the
innodb_max_dirty_pages_pct_lwm
system variable changed from0
(%) to10
(%). Withinnodb_max_dirty_pages_pct_lwm=10
, InnoDB increases its flushing activity when >10% of the buffer pool contains modified (‘dirty’) pages. The purpose of this change is to trade off peak throughput slightly, in exchange for more consistent performance.The default value of the
innodb_max_dirty_pages_pct
system variable changed from75
(%) to90
(%). This change combines with the change toinnodb_max_dirty_pages_pct_lwm
and together they ensure a smooth InnoDB flushing behavior, avoiding flushing bursts. To revert to the previous behavior, setinnodb_max_dirty_pages_pct=75
andinnodb_max_dirty_pages_pct_lwm=0
.
Performance Schema Defaults
Performance Schema Meta Data Locking (MDL) instrumentation is turned on by default. The compiled default for
performance-schema-instrument='wait/lock/metadata/sql/%=ON'
changed fromOFF
toON
. This is an enabler for adding MDL oriented views in SYS.Performance Schema Memory instrumentation is turned on by default. The compiled default for
performance-schema-instrument='memory/%=COUNTED'
changed fromOFF
toCOUNTED
. This is important because the accounting is incorrect if instrumentation is enabled after server start, and you could get a negative balance from missing an allocation, but catching a free.Performance Schema Transaction instrumentation is turned on by default. The compiled default for
performance-schema-consumer-events-transactions-current=ON
,performance-schema-consumer-events-transactions-history=ON
, andperformance-schema-instrument='transaction%=ON'
changed fromOFF
toON
.
Replication Defaults
The default value of the
log_bin
system variable changed fromOFF
toON
. In other words, binary logging is enabled by default. Nearly all production installations have the binary log enabled as it is used for replication and point-in-time recovery. Thus, by enabling binary log by default we eliminate one configuration step, enabling it later requires a mysqld restart. Enabling it by default also provides better test coverage and it becomes easier to spot performance regressions. Remember to also setserver_id
(see following change). The 8.0 default behavior is as if you issued./mysqld --log-bin --server-id=1
. If you are on 8.0 and want 5.7 behavior you can issue./mysqld --skip-log-bin --server-id=0
.The default value of the
server_id
system variable changed from0
to1
(combines with the change tolog_bin=ON
). The server can be started with this default ID, but in practice you must set theserver-id
according to the replication infrastructure being deployed, to avoid having duplicate server ids.The default value of the
log-slave-updates
system variable changed fromOFF
toON
. This causes a replica to log replicated events into its own binary log. This option is required for Group Replication, and also ensures correct behavior in various replication chain setups, which have become the norm today.The default value of the
expire_logs_days
system variable changed from0
to30
. The new default30
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 of0
disables any automatic binary log purges.The default value of the
master_info_repository
andrelay_log_info_repository
system variables change fromFILE
toTABLE
. 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 fromOFF
toXXHASH64
. 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 fromINDEX_SCAN,TABLE_SCAN
toINDEX_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 from16M
to128M
. This change increases the amount of memory available to multithreaded replicas.The default value of the
gtid_executed_compression_period
system variable changed from1000
to0
. This change ensures that compression of themysql.gtid_executed
table only occurs implicitly as required.
Group Replication Defaults
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 thegroup_replication_unreachable_majority_timeout
setting is reached.The default value of
group_replication_exit_state_action
changed fromABORT_SERVER
toREAD_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.
Most of these defaults are reasonably good for both development
and production environments. An exception to this is the
--innodb-dedicated-server
option,
whose default value remains OFF
, although we
recommend 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 using
--innodb-dedicated-server
, which
determines values for the following InnoDB variables (if not
specified explicitly), based on available memory:
innodb_buffer_pool_size
,
innodb_log_file_size
, and
innodb_flush_method
. See
Section 17.8.12, “Enabling Automatic InnoDB 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 where you need your old 5.7 value, set the corresponding configuration variable or startup option in your operational environment.
MySQL 8.0 has the Performance Schema
variables_info
table, which shows
for each system variable the source from which it was most
recently set, as well as its range of values. This provides SQL
access to all there is to know about a configuration variable
and its values.
Performance regressions are expected between MySQL versions 5.7 and 8.0. MySQL 8.0 has more features, changes default values, is more robust, and adds security functionality and additional diagnostic information. Listed here are valid reasons for regressions between these versions which includes potential mediation options. This is not an exhaustive list.
Changes related to default values changing between MySQL versions 5.7 and 8.0:
Binary logs are disabled by default in 5.7, and enabled by default in 8.0.
Mediation: Disable binary logging by specifying the
--skip-log-bin
or--disable-log-bin
option at startup.The default character set changed from
latin1
toutf8mb4
in 8.0. Whileutf8mb4
performs significantly better in 8.0 than it did in 5.7,latin1
is faster thanutf8mb4
.Mediation: Use
latin1
in 8.0 ifutf8mb4
is not needed.
Transactional Data Dictionary (atomic DDL) was introduced in 8.0.
This increases robustness/reliability at the expense of DDL performance (CREATE / DROP intensive loads), but it should not impact the DML load (SELECT / INSERT / UPDATE / DELETE).
Mediation: None
The more modern TLS ciphers/algorithms used as of 5.7.28 has an effect when TLS (SSL) is enabled (the default):
Before MySQL 5.7.28, MySQL uses the yaSSL library for the community edition and OpenSSL for the enterprise edition.
As of MySQL 5.7.28, MySQL only uses OpenSSL with its stronger TLS ciphers, which are more costly in terms of performance.
Upgrading to MySQL 8.0 from MySQL 5.7.28 or earlier can cause a TLS performance regression.
Mediation: None (if TLS is required for security reasons)
Performance Schema (PFS) instrumentation is much wider in 8.0 than in 5.7:
PFS cannot be compiled out in MySQL 8.0 but it can be turned off. Some performance schema instrumentation will still exist even when turned off, but overhead will be smaller.
Mediation: Set performance_schema = OFF in 8.0, or turn off performance schema instrumentation at finer granularity if some but not all PFS functionality is needed.
Truncating undo tablespaces is enabled by default in 8.0 which can significantly impact performance:
Historically InnoDB stored undo logs in the system tablespace but there was no way to reclaim space used by undo log. The system tablespace would only grow and not shrink, and this inspired feature requests to remedy this.
MySQL 8.0 moved the undo log to separate tablespaces which allows both manual and automatic undo log truncation.
However, auto-truncation has a permanent performance overhead and it can potentially cause stalls.
Mediation: Set innodb_undo_log_truncate = OFF in 8.0, and manually truncate undo logs as needed. For related information, see Truncating Undo Tablespaces.
The character classes [[:alpha:]]
or
[[:digit:]]
do not perform as well with
regular expression functions such as REGEXP()
and RLIKE()
in MySQL 8.0 as they did in MySQL
5.7. This is due to the replacement in MySQL 8.0 of the Spencer
regular expression library with the ICU library, which uses
UTF-16 internally.
Mediation: In place of
[[:alpha:]]
, use [a-zA-Z]
;
in place of [[:digit:]]
, use
[0-9]
.