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https://dev.mysql.com/doc/refman/8.4/en/optimizing-queries-myisam.html
This updates a value for each index part that indicates the average number of rows that have the same value. This is a good way to make queries faster if you have a unique index from which you want to read all rows in order according to the index.
https://dev.mysql.com/doc/refman/8.4/en/order-by-optimization.html
A condition for index use is that the index must have the same homogeneity, but need not have the same actual direction. (This is the first table in the EXPLAIN output that does not have a const join type.) The query has different ORDER BY and GROUP ... This section describes when MySQL can use an index to satisfy an ORDER BY clause, the filesort operation used when an index cannot be used, and execution plan information available from the optimizer about ORDER ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-columns-range.html
A value_list must be supplied for each partition definition, and each value_list must have the same number of values as the column_list has columns. However, the order of the column names in the partitioning column list and the value lists does not ... Range columns partitioning is similar to range partitioning, but enables you to define partitions using ranges based on multiple column ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-handling-nulls.html
Partitioning in MySQL does nothing to disallow NULL as the value of a partitioning expression, whether it is a column value or the value of a user-supplied expression. Even though it is permitted to use NULL as the value of an expression that must ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-limitations-storage-engines.html
Partitioned InnoDB tables cannot have foreign key references, nor can they have columns referenced by foreign keys. InnoDB tables which have or which are referenced by foreign keys cannot be partitioned. CREATE TABLE and ALTER TABLE statements that ... In MySQL 8.4, partitioning support is not actually provided by the MySQL Server, but rather by a table storage engine's own or native partitioning ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-events-transactions-current-table.html
For example, the events_transactions_history and events_transactions_history_long tables are collections of the most recent transaction events that have ended, up to a maximum number of rows per thread and globally across all threads, respectively.
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-metadata-locks-table.html
The Performance Schema exposes metadata lock information through the metadata_locks table: Locks that have been granted (shows which sessions own which current metadata locks). Locks that have been requested but not yet granted (shows which sessions ... MySQL uses metadata locking to manage concurrent access to database objects and to ensure data consistency; see Section 10.11.4, “Metadata ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-rwlock-instances-table.html
An rwlock is a synchronization mechanism used in the code to enforce that threads at a given time can have access to some common resource following certain rules. The access is either shared (many threads can have a read lock at the same time), ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-statement-summary-tables.html
In other words, for a given digest, 95% of the statements measured have a latency lower than QUANTILE_95. The row with DIGEST = NULL is maintained because Performance Schema tables have a maximum size due to memory constraints. The Performance ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-statement-tables.html
events_statements_history: The most recent statement events that have ended per thread. events_statements_history_long: The most recent statement events that have ended globally (across all threads). Instruments for commands have names that begin ...