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https://dev.mysql.com/doc/refman/8.4/en/innodb-page-compression.html
Writes to the tablespace that occur after setting the new compression algorithm use the new setting, but to apply the new compression algorithm to existing pages, you must rebuild the table using OPTIMIZE TABLE. ALTER TABLE t1 COMPRESSION="zlib"; ...
https://dev.mysql.com/doc/refman/8.4/en/known-issues.html
The following problems are known: Subquery optimization for IN is not as effective as for =. SELECT with no ORDER BY, the SELECT may return rows in a different order (which results in a row having different ranks, hence getting a different number in ... This section lists known issues in recent versions of ...
https://dev.mysql.com/doc/refman/8.4/en/mysql-indexes.html
If the table has a multiple-column index, any leftmost prefix of the index can be used by the optimizer to look up rows. This is optimized by a preprocessor that checks whether you are using WHERE key_part_N = constant on all key parts that occur ...
https://dev.mysql.com/doc/refman/8.4/en/outer-join-simplification.html
When the optimizer evaluates plans for outer join operations, it takes into consideration only plans where, for each such operation, the outer tables are accessed before the inner tables. The optimizer choices are limited because only such plans ...
https://dev.mysql.com/doc/refman/8.4/en/privileges-provided.html
INSERT is also required for the ANALYZE TABLE, OPTIMIZE TABLE, and REPAIR TABLE table-maintenance statements. OPTIMIZE_LOCAL_TABLE Enables use of OPTIMIZE LOCAL TABLE and OPTIMIZE NO_WRITE_TO_BINLOG TABLE statements. A user with this privilege can ... The privileges granted to a MySQL account determine which operations the account can ...
https://dev.mysql.com/doc/refman/8.4/en/server-status-variables.html
This read method is mainly used to optimize ORDER BY ... Last_query_cost The total cost of the last compiled query as computed by the query optimizer. Last_query_partial_plans The number of iterations the query optimizer made in execution plan ...
https://dev.mysql.com/doc/refman/8.4/en/subquery-restrictions.html
(See Section 10.2.2.4, “Optimizing Derived Tables, View References, and Common Table Expressions with Merging or Materialization”.) Example: UPDATE t ... In general, you may be able to influence the optimizer to materialize a derived table by ...
https://dev.mysql.com/doc/refman/8.4/en/system-variables-controlling-tracing.html
The following system variables affect optimizer tracing: optimizer_trace: Enables or disables optimizer tracing. optimizer_trace_features: Enables or disables selected features of the MySQL Optimizer, using the syntax shown here: SET ...
https://dev.mysql.com/doc/refman/8.4/en/timestamp-lookups.html
This phenomenon can lead to different results for a given TIMESTAMP column query, depending on whether the optimizer uses an index to execute the query. Under those conditions, the comparison in the WHERE clause occurs in different ways for ...
https://dev.mysql.com/doc/refman/8.4/en/tracing-example.html
Now we can examine the trace, whose first column (QUERY), containing the original statement to be traced, is shown here: SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE\G *************************** 1. If a statement uses subqueries, there can be ...row *************************** QUERY: SELECT SUM(alias2.col_varchar_nokey) AS c1, alias2.pk AS c2 FROM t1 AS alias1 STRAIGHT_JOIN t2 AS alias2 ON alias2.pk = alias1.col_int_key WHERE alias1.pk GROUP BY c2 ORDER BY alias1.col_int_key, alias2.pk This can be useful mark when several traces are ...