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https://dev.mysql.com/doc/refman/8.0/en/innodb-auto-increment-handling.html
The index is not required to be a PRIMARY KEY or UNIQUE, but to avoid duplicate values in the AUTO_INCREMENT column, those index types are recommended. In this lock mode, auto-increment values are guaranteed to be unique and monotonically increasing ... InnoDB provides a configurable locking mechanism that can significantly improve scalability and performance of SQL statements that add rows to tables with AUTO_INCREMENT ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-operations.html
When you create a UNIQUE or PRIMARY KEY index, MySQL must do some extra work. For UNIQUE indexes, MySQL checks that the table contains no duplicate values for the key. If you create a table without a primary key, InnoDB chooses one for you, which ...
https://dev.mysql.com/doc/refman/8.0/en/invisible-columns.html
Index definitions can name invisible columns, including definitions for PRIMARY KEY and UNIQUE indexes. For statements that insert or ignore new rows, or that replace or modify existing rows, based on values in a PRIMARY KEY or UNIQUE index, MySQL ...An invisible column is normally hidden to queries, but can be accessed if explicitly ...
https://dev.mysql.com/doc/refman/8.0/en/known-issues.html
If you use ALTER TABLE to add a UNIQUE index to a table used in a MERGE table and then add a normal index on the MERGE table, the key order is different for the tables if there was an old, non-UNIQUE key in the table. This is because ALTER TABLE ...
https://dev.mysql.com/doc/refman/8.0/en/memory-storage-engine.html
The MEMORY storage engine (formerly known as HEAP) creates special-purpose tables with contents that are stored in memory. Because the data is vulnerable to crashes, hardware issues, or power outages, only use these tables as temporary work areas ...
https://dev.mysql.com/doc/refman/8.0/en/merge-storage-engine.html
There it is indexed but not as a PRIMARY KEY because a MERGE table cannot enforce uniqueness over the set of underlying tables. The MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be ...
https://dev.mysql.com/doc/refman/8.0/en/multiple-data-directories.html
If (despite this warning) you run multiple servers using the same data directory and they have logging enabled, you must use the appropriate options to specify log file names that are unique to each server. Also, modify any other options that must ... Each MySQL Instance on a machine should have its own data ...
https://dev.mysql.com/doc/refman/8.0/en/myisamchk-table-info.html
To obtain a description of a MyISAM table or statistics about it, use the commands shown here. The output from these commands is explained later in this section. myisamchk -d tbl_name Runs myisamchk in “describe mode” to produce a description ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-config-example.html
Another deviation is that sections are not uniquely identified by section name. Instead, unique sections (such as two different nodes of the same type) are identified by a unique ID specified as a parameter within the section. To support NDB ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-config-starting.html
You may for the sake of convenience specify # a NodeId for any management server, although one is allocated # for it automatically; if you do so, it must be in the range 1-255 # inclusive and must be unique among all IDs specified for cluster # ...