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https://dev.mysql.com/doc/refman/8.4/en/performance-schema-mutex-instances-table.html
The work performed while holding a mutex is said to be in a “critical section,” and multiple queries do execute this critical section in a serialized way (one at a time), which is a potential bottleneck. By performing queries on both of the ...
https://dev.mysql.com/doc/refman/8.4/en/row-subqueries.html
Scalar or column subqueries return a single value or a column of values. A row constructor is used for comparisons with subqueries that return two or more columns. A row subquery is a subquery variant that returns a single row and can thus return ...
https://dev.mysql.com/doc/refman/8.4/en/server-loadable-functions.html
MySQL supports loadable functions, that is, functions that are not built in but can be loaded at runtime (either during startup or later) to extend server capabilities, or unloaded to remove capabilities. For a table describing the available ...
https://dev.mysql.com/doc/refman/8.4/en/sys-sys-config.html
Otherwise, it must be the name of an existing view that queries the Performance Schema events_statements_summary_by_digest table. This table contains sys schema configuration options, one row per option. Configuration changes made by updating this ...
https://dev.mysql.com/doc/refman/8.4/en/table-cache.html
MySQL is multithreaded, so there may be many clients issuing queries for a given table simultaneously. For example, for 200 concurrent running connections, specify a table cache size of at least 200 * N, where N is the maximum number of tables per ... When you execute a mysqladmin status command, you should see something like this: Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12 The Open tables value of 12 can be somewhat puzzling if you have fewer than 12 ...
https://dev.mysql.com/doc/refman/8.4/en/thread-pool-operation.html
The thread_pool_transaction_delay setting does not affect queries issued from a privileged connection (a connection assigned to the Admin thread group). The thread pool consists of a number of thread groups, each of which manages a set of client ...
https://dev.mysql.com/doc/refman/8.4/en/thread-pool-tuning.html
The product of this value and the thread pool size is approximately equal to the total number of threads available to process queries. Greater values for thread_pool_query_threads_per_group value make it less likely that all the threads in the ...
https://dev.mysql.com/doc/refman/8.4/en/tracing-example.html
If a statement uses subqueries, there can be mutliple preparations, optimizations, and executions, as well as subquery-specific transformations. Now we can examine the trace, whose first column (QUERY), containing the original statement to be ...
https://dev.mysql.com/doc/refman/8.4/en/xa-states.html
An XA transaction progresses through the following states: Use XA START to start an XA transaction and put it in the ACTIVE state. For an ACTIVE XA transaction, issue the SQL statements that make up the transaction, and then issue an XA END ...
https://dev.mysql.com/doc/c-api/8.4/en/c-api-data-structures.html
Tip To view the MYSQL_FIELD member values for result sets interactively, start the mysql client with the --column-type-info option, then execute some sample queries. This section describes C API data structures other than those used for prepared ...