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https://dev.mysql.com/doc/refman/8.0/en/merge-table-problems.html
In some cases, differing PACK_KEYS table option values among the MERGE and underlying tables cause unexpected results if the underlying tables contain CHAR or BINARY columns. The following are known problems with MERGE tables: MERGE child tables ...
https://dev.mysql.com/doc/refman/8.0/en/monitor-innodb-mutex-waits-performance-schema.html
$> ./mysqlslap --auto-generate-sql --concurrency=100 --iterations=10 --number-of-queries=1000 --number-char-cols=6 --number-int-cols=6; Query the wait event data. A mutex is a synchronization mechanism used in the code to enforce that only one ...
https://dev.mysql.com/doc/refman/8.0/en/myisam-storage-engine.html
MyISAM tables have the following characteristics: All data values are stored with the low byte first. MyISAM also supports the following features: Support for a true VARCHAR type; a VARCHAR column starts with a length stored in one or two bytes.
https://dev.mysql.com/doc/refman/8.0/en/myisamchk-general-options.html
This is often the case when you have large key values for CHAR, VARCHAR, or TEXT columns, because the sort operation needs to store the complete key values as it proceeds. The options described in this section can be used for any type of table ...
https://dev.mysql.com/doc/refman/8.0/en/myisamchk-table-info.html
uint24 NULL 0 1024 Field Start Length Nullpos Nullbit Type 1 1 1 2 2 4 no zeros 3 6 81 varchar 4 87 81 varchar 5 168 3 1 1 no zeros 6 171 3 1 2 no zeros Explanations for the types of information myisamchk produces are given here. varchar prefix 0 ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-disk-data-storage-requirements.html
For example, converting a CHAR(4) column from memory-based to disk-based format increases the amount of DataMemory used per row from 4 to 8 bytes. The following items apply to Disk Data storage requirements: Variable-length columns of Disk Data ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-limitations-database-objects.html
For memory-based columns, you can work around this limitation by using a variable-width column type such as VARCHAR or defining the column as COLUMN_FORMAT=DYNAMIC; this does not work with columns stored on disk. Some database objects such as ...
https://dev.mysql.com/doc/refman/8.0/en/numeric-type-attributes.html
For example, applications can use the LPAD() function to zero-pad numbers up to the desired width, or they can store the formatted numbers in CHAR columns. MySQL supports an extension for optionally specifying the display width of integer data ...
https://dev.mysql.com/doc/refman/8.0/en/numeric-type-syntax.html
For example, applications could use the LPAD() function to zero-pad numbers up to the desired width, or they could store the formatted numbers in CHAR columns. For integer data types, M indicates the minimum display width. Display width is ...
https://dev.mysql.com/doc/refman/8.0/en/order-by-optimization.html
For example, if only the first 10 bytes of a CHAR(20) column are indexed, the index cannot distinguish values past the 10th byte and a filesort is needed. (A symptom of setting the value of this variable too high is a combination of high disk ...