Search Results
https://dev.mysql.com/doc/refman/8.4/en/mrr-optimization.html
With the Disk-Sweep Multi-Range Read (MRR) optimization, MySQL tries to reduce the number of random disk access for range scans by first scanning the index only and collecting the keys for the relevant rows. Then the keys are sorted and finally the ... Reading rows using a range scan on a secondary index can result in many random disk accesses to the base table when the table is large and not stored in the storage engine's ...
https://dev.mysql.com/doc/refman/8.4/en/myisamchk-memory.html
For example, if you have more than 512MB RAM available, you could use options such as these (in addition to any other options you might specify): myisamchk --myisam_sort_buffer_size=256M \ --key_buffer_size=512M \ --read_buffer_size=64M \ ...
https://dev.mysql.com/doc/refman/8.4/en/myisamchk-repair-options.html
--keys-used=val, -k val Command-Line Format --keys-used=val Type Numeric For myisamchk, the option value is a bit value that indicates which indexes to update. You can specify this option twice to force myisamchk to modify the original data file in ...--correct-checksum Command-Line Format --correct-checksum Correct the checksum information for the ...
https://dev.mysql.com/doc/refman/8.4/en/myisamchk.html
The myisamchk utility gets information about your database tables or checks, repairs, or optimizes them. myisamchk works with MyISAM tables (tables that have .MYD and .MYI files for storing data and indexes). You can also use the CHECK TABLE and ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-handling-nulls.html
NULL is handled somewhat differently for tables partitioned by HASH or KEY. For tables that are partitioned by HASH or KEY, this result is treated for determining the correct partition as 0. Partitioning in MySQL does nothing to disallow NULL as ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-maintenance.html
Example: ALTER TABLE t1 REPAIR PARTITION p0,p1; Normally, REPAIR PARTITION fails when the partition contains duplicate key errors. You can use ALTER IGNORE TABLE with this option, in which case all rows that cannot be moved due to the presence of ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-error-summary-tables.html
The error summary tables have these indexes: events_errors_summary_by_account_by_error: Primary key on (USER, HOST, ERROR_NUMBER) events_errors_summary_by_host_by_error: Primary key on (HOST, ERROR_NUMBER) events_errors_summary_by_thread_by_error: ... The Performance Schema maintains summary tables for aggregating statistical information about server errors (and ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-memory-summary-tables.html
The memory summary tables have these indexes: memory_summary_by_account_by_event_name: Primary key on (USER, HOST, EVENT_NAME) memory_summary_by_host_by_event_name: Primary key on (HOST, EVENT_NAME) memory_summary_by_thread_by_event_name: Primary ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-optimization.html
row *************************** Table: accounts Non_unique: 0 Key_name: ACCOUNT Seq_in_index: 1 Column_name: USER Collation: NULL Cardinality: NULL Sub_part: NULL Packed: NULL Null: YES Index_type: HASH Comment: Index_comment: Visible: YES ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-stage-summary-tables.html
The stage summary tables have these indexes: events_stages_summary_by_account_by_event_name: Primary key on (USER, HOST, EVENT_NAME) events_stages_summary_by_host_by_event_name: Primary key on (HOST, EVENT_NAME) ... The Performance Schema maintains ...