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https://dev.mysql.com/doc/refman/8.4/en/index-statistics.html
Storage engines collect statistics about tables for use by the optimizer. Table statistics are based on value groups, where a value group is a set of rows with the same key prefix value. The average value group size is related to table cardinality, ...For optimizer purposes, an important statistic is the average value group ...
https://dev.mysql.com/doc/refman/8.4/en/innodb-online-ddl-limitations.html
The following limitations apply to online DDL operations: The table is copied when creating an index on a TEMPORARY TABLE. The ALTER TABLE clause LOCK=NONE is not permitted if there are ON...CASCADE or ON...SET NULL constraints on the table. Before ...When the DML operations are applied, it is possible to encounter a duplicate key entry error (ERROR 1062 (23000): Duplicate entry), even if the duplicate entry is only temporary and would be reverted by a later entry in the online ...
https://dev.mysql.com/doc/refman/8.4/en/replication-rbr-usage.html
As noted in Section 19.5.1.31, “Replication and Temporary Tables”, temporary tables are not replicated when using row-based or mixed format. Temporary tables are not replicated when using row-based or mixed format because there is no need. In ...
https://dev.mysql.com/doc/refman/8.4/en/replication-solutions-diffengines.html
It does not matter for the replication process whether the original table on the source and the replicated table on the replica use different storage engine types. For example, in a typical scale-out scenario (see Section 19.4.5, “Using ...This ...
https://dev.mysql.com/doc/refman/8.4/en/timestamp-initialization.html
For any TIMESTAMP or DATETIME column in a table, you can assign the current timestamp as the default value, the auto-update value, or both: An auto-initialized column is set to the current timestamp for inserted rows that specify no value for the ...
https://dev.mysql.com/doc/refman/8.4/en/group-by-optimization.html
The most general way to satisfy a GROUP BY clause is to scan the whole table and create a new temporary table where all rows from each group are consecutive, and then use this temporary table to discover groups and apply aggregate functions (if ...
https://dev.mysql.com/doc/refman/8.4/en/charset-unicode-conversion.html
In terms of table content, conversion from utf8mb3 to utf8mb4 presents no problems: For a BMP character, utf8mb4 and utf8mb3 have identical storage characteristics: same code values, same encoding, same length. In terms of table structure, these are ... This section describes issues that you may face when converting character data between the utf8mb3 and utf8mb4 character ...
https://dev.mysql.com/doc/refman/8.4/en/engine-condition-pushdown-optimization.html
Joins are not directly supported; conditions involving multiple tables are pushed separately where possible. Previously, engine condition pushdown was limited to terms referring to column values from the same table to which the condition was being ... This optimization improves the efficiency of direct comparisons between a nonindexed column and a ...
https://dev.mysql.com/doc/ndbapi/en/ndb-start-mysql-data-types.html
This section provides information about the way in which MySQL data types are represented in NDBCLUSTER table columns and how these values can be accessed in NDB API applications. make_ndb_varchar(myVal, "NDB is way cool!!"); ...The MySQL TINYINT, ...
https://dev.mysql.com/doc/refman/8.4/en/invisible-indexes.html
ALTER INDEX operation: ALTER TABLE t1 ALTER INDEX i_idx INVISIBLE; ALTER TABLE t1 ALTER INDEX i_idx VISIBLE; Information about whether an index is visible or invisible is available from the Information Schema STATISTICS table or SHOW INDEX output.