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https://dev.mysql.com/doc/internals/en/class-procedure-change-columns.html
Prototype: virtual bool change_columns(List<Item> &field_list); Here you can change the structure of the result field list, for example, you can add fields to the field_list or replace the queries result fields by something completely different ...
https://dev.mysql.com/doc/internals/en/cowork-with-dbug-facility.html
When running the MySQL test suite with a "debug" server (the DBUG facility is configured in) and the --debug command line option, the Debug Sync Facility writes trace messages to the DBUG trace. The following shell commands proved very useful in ...
https://dev.mysql.com/doc/internals/en/general-trace-structure.html
A trace follows closely the actual execution path: there is a join-preparation object, a join-optimization object, a join-execution object, for each JOIN. Query transformations (IN->EXISTS, outer join to inner join...), simplifications (elimination ...
https://dev.mysql.com/doc/internals/en/guided-tour-major-directories-test.html
If you just want to debug some queries with the embedded server (not the test), it's easier to just run libmysqld/examples/mysql. To run a test named some.test with the debugger in embedded mode you could do this: Run libmysqld/examples/test_run ...
https://dev.mysql.com/doc/internals/en/implementing-basic-table-scanning.html
Such engines might be used to support SQL queries of logs and other data files that are populated outside of MySQL. The implementation of the methods in this section provide the first steps toward the creation of more advanced storage engines.
https://dev.mysql.com/doc/internals/en/implementing-records-in-range-method.html
The [custom-engine.html#custom-engine-api-reference-records_in_range records_in_range()] method is called by the optimizer to assist in choosing which index on a table to use for a query or join. It is defined as follows: ha_rows ...
https://dev.mysql.com/doc/internals/en/implementing-the-info-method.html
These values are also used to populate certain SHOW outputs such as SHOW TABLE STATUS and for queries of the INFORMATION_SCHEMA. The optimizer requests an update of table information by calling the ...
https://dev.mysql.com/doc/internals/en/indexing-overview.html
Adding index support to a storage engine revolves around two tasks: providing information to the optimizer and implementing index-related methods. The information provided to the optimizer helps the optimizer to make better decisions about which ...
https://dev.mysql.com/doc/internals/en/information-schema-optimizer-trace-table.html
TRACE: The trace, in JSON format (see json.org: basically it has scalars (number, string, bool) and structures (either arrays or associative arrays)).
https://dev.mysql.com/doc/internals/en/join-buffer-size.html
Basic information about the join buffer cache: The size of each join buffer is determined by the value of the join_buffer_size system variable. This buffer is used only when the join is of type ALL or index (in other words, when no possible keys ...