https://dev.mysql.com/optimizing-innodb-storage-layout.html
Use the VARCHAR data type instead of CHAR to store variable-length strings or for columns with many NULL values. A CHAR(N) column always takes N characters to store data, even if the string is shorter or its value is NULL. Once your data reaches a ...
https://dev.mysql.com/performance-schema-atom-molecule-events.html
For example, a row fetch might result in rows like this: Row# EVENT_NAME TIMER_START TIMER_END ---- ---------- ----------- --------- 1 wait/io/file/myisam/dfile 10001 10002 2 wait/io/table/sql/handler 10000 NULL The row fetch causes a file read. In ... For a table I/O event, there are usually two rows in events_waits_current, not ...
https://dev.mysql.com/performance-schema-obtaining-parent-events.html
FROM performance_schema.events_transactions_current AS parent INNER JOIN performance_schema.data_locks AS child WHERE parent.THREAD_ID = child.THREAD_ID AND parent.EVENT_ID < child.EVENT_ID AND ( child.EVENT_ID <= parent.END_EVENT_ID OR ...Rows of ...
https://dev.mysql.com/performance-schema-stage-tables.html
The Performance Schema instruments stages, which are steps during the statement-execution process, such as parsing a statement, opening a table, or performing a filesort operation. Stages correspond to the thread states displayed by SHOW ...
https://dev.mysql.com/primary-key-optimization.html
Query performance benefits from the NOT NULL optimization, because it cannot include any NULL values. The primary key for a table represents the column or set of columns that you use in your most vital queries. With the InnoDB storage engine, the ...
https://dev.mysql.com/proxy-users.html
Two system variables help trace the proxy login process: proxy_user: This value is NULL if proxying is not used. If the plugin does not set this variable, its value is NULL. The plugin that authenticates a given connection may request that the ...
https://dev.mysql.com/referential-constraints-table.html
The possible values are CASCADE, SET NULL, SET DEFAULT, RESTRICT, NO ACTION. The possible values are CASCADE, SET NULL, SET DEFAULT, RESTRICT, NO ACTION. The REFERENTIAL_CONSTRAINTS table has these columns: CONSTRAINT_CATALOG The name of the catalog ...
https://dev.mysql.com/replication-administration-status.html
row *************************** Id: 10 User: root Host: slave1:58371 db: NULL Command: Binlog Dump Time: 777 State: Has sent all binlog to slave; waiting for binlog to be updated Info: NULL Because it is the slave that drives the replication ... The ...
https://dev.mysql.com/replication-options-binary-log.html
Otherwise, if the table has a unique key all of whose columns are NOT NULL, then only the columns in the unique key need be logged. (If the table has neither a primary key nor a unique key without any NULL columns, then all columns must be used in ... Startup Options Used with Binary Logging System Variables Used with Binary Logging You can use the mysqld options and system variables that are described in this section to affect the operation of the binary log as well as to control which statements are written to the binary ...
https://dev.mysql.com/rewriter-query-rewrite-plugin-reference.html
If no error occurs when the rules table is loaded into memory, the plugin sets the message column to NULL. A non-NULL value indicates an error and the column contents are the error message. Users communicate with the plugin by modifying the set of ...
