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https://dev.mysql.com/doc/refman/8.0/en/upgrade-before-you-begin.html
The backup should include the mysql system database, which contains the MySQL data dictionary tables and system tables. It is therefore imperative that you back up your data before starting the upgrade process. If your MySQL installation contains a ...The only supported alternative is to restore a backup taken before ...Important Downgrade from MySQL 8.0 to MySQL 5.7, or ...
https://dev.mysql.com/doc/refman/8.0/en/replace.html
To use REPLACE, you must have both the INSERT and DELETE privileges for the table. As with INSERT, if it is not possible to insert the new row into any of these partitions or subpartitions, the REPLACE statement fails with the error Found a row not ...REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-mysqld.html
If you build MySQL from source, you must invoke CMake with the -DWITH_NDB=1 or (deprecated) -DWITH_NDBCLUSTER=1 option to include support for NDB. Insert a line containing ndbcluster in the [mysqld] section of your my.cnf file. (We often refer to a ...To be used with NDB Cluster, mysqld needs to be built with support for the NDB storage engine, as it is in the precompiled binaries available from ...For more information about compiling NDB Cluster from source, see ...
https://dev.mysql.com/doc/refman/8.0/en/replication-solutions-performance.html
Figure 19.3 Using an Additional Replication Source to Improve Performance For this to work, you must configure the MySQL instances as follows: Source 1 is the primary source where all changes and updates are written to the database. If your replicas ...Also, as each replica must receive a full copy of the source's binary log, the network load on the source may also increase and create a ... As the number ...
https://dev.mysql.com/doc/refman/8.0/en/cost-model.html
The optimizer also has a database of cost estimates to use during execution plan construction. These estimates are stored in the server_cost and engine_cost tables in the mysql system database and are configurable at any time. Cost Model General ...
https://dev.mysql.com/doc/refman/8.0/en/alter-user.html
To modify an account that uses passwordless authentication, you must have the PASSWORDLESS_USER_ADMIN privilege. If the IF EXISTS clause is given, the statement produces a warning for each named user that does not exist, rather than an error. It ...
https://dev.mysql.com/doc/refman/8.0/en/bnl-bka-optimization.html
In the example just given, the buffer B1 used to join tables t1 and t2 must be a regular buffer. Then the BKA algorithm builds keys to access the table to be joined for all rows in the buffer and submits these keys in a batch to the database engine ... In MySQL, a Batched Key Access (BKA) Join algorithm is available that uses both index access to the joined table and a join ...
https://dev.mysql.com/doc/refman/8.0/en/windows-pluggable-authentication.html
The file must be located in the directory named by the plugin_dir system variable. To be usable by the server, the plugin library file must be located in the MySQL plugin directory (the directory named by the plugin_dir system variable). The client ... Note Windows pluggable authentication is an extension included in MySQL Enterprise Edition, a commercial ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-variables-info-table.html
This includes variables set within files specified using the init_file system variable. EXPLICIT The variable was set from an option file named with the --defaults-file option. EXTRA The variable was set from an option file named with the ... The ...
https://dev.mysql.com/doc/refman/8.0/en/problems-with-null.html
To load a NULL value into a column, use \N in the data file. The following statement returns no rows, because expr = NULL is never true for any expression: mysql> SELECT * FROM my_table WHERE phone = NULL; To look for NULL values, you must use the ... The concept of the NULL value is a common source of confusion for newcomers to SQL, who often think that NULL is the same thing as an empty string ...