Instead of the usual result output, MySQL would then show its statement execution plan by explaining which processes take place in which order when executing the statement. For a simple query, it would look like the following: EXPLAIN SELECT * FROM foo WHERE foo.bar = 'infrastructure as a service' OR foo.bar = 'iaas' In MySQL, EXPLAIN can be used in front of a query beginning with SELECT, INSERT, DELETE, REPLACE, and UPDATE. The EXPLAIN keyword is used throughout various SQL databases and provides information about how your SQL database executes a query. Why are there 5 joins and why is there an ORDER BY used within a subquery before one of the joins even happens? Remember, you were hired for a reason - most likely, that reason also has to do with many convoluted queries that were created and edited over the last decade. See Defragmenting InnoDB Tablespaces for more details.You’re in your new job as Database Administrator or Data Engineer and you just got lost trying to figure out what these insane looking queries are supposed to mean and do. Note that tablespace files (including ibdata1) will not shrink as the result of defragmentation, but one will get better memory utilization in the InnoDB buffer pool as there are fewer data pages in use. #Heidisql mysql optimizer full#Instead, this feature loads n pages (determined by innodb-defragment-n-pages) and tries to move records so that pages would be full of records and then frees pages that are fully empty after the operation. No new tables are created and there is no need to copy data from old tables to new tables. For this functionality to be enabled, the innodb_defragment system variable must be enabled. MariaDB 10.1.1 merged the Facebook/Kakao defragmentation patch, allowing one to use OPTIMIZE TABLE to defragment InnoDB tablespaces. You can run multiple OPTIMIZE statements to fully re-organize the index. Since fulltext re-organization can take a long time, the innodb_ft_num_word_optimize variable limits the re-organization to a number of words (2000 by default). This is intended to be a temporary setting, and should be reset to 0 once the fulltext index has been re-organized. #Heidisql mysql optimizer update#In order to use it to update fulltext index statistics, the innodb_optimize_fulltext_only system variable must be set to 1. The fulltext index is only fully re-organized when an OPTIMIZE TABLE statement is run.īy default, an OPTIMIZE TABLE will defragment a table. Change statistics are stored in a separate location. When rows are added or deleted to an InnoDB fulltext index, the index is not immediately re-organized, as this can be an expensive operation. If a MyISAM table is fragmented, concurrent inserts will not be performed until an OPTIMIZE TABLE statement is executed on that table, unless the concurrent_insert server system variable is set to ALWAYS. The Aria storage engine supports progress reporting for this statement. This operation frees the unused space and updates index statistics. However, if the server has been started with the -skip-new option, OPTIMIZE TABLE is linked to ALTER TABLE, and recreates the table. With other storage engines, OPTIMIZE TABLE does nothing by default, and returns this message: " The storage engine for the table doesn't support optimize". You can use OPTIMIZE TABLE to reclaim the unused OPTIMIZE TABLE is also supported for partitioned tables. The NO_WRITE_TO_BINLOG keyword ( LOCAL is an alias) will ensure the statement is not written to the binary log.įrom MariaDB 10.3.19, OPTIMIZE TABLE statements are not logged to the binary log if read_only is set. This statement requires SELECT and INSERT privileges for the table.īy default, OPTIMIZE TABLE statements are written to the binary log and will be replicated. Linked list and subsequent INSERT operations reuse old row positions. Rows (tables that have VARCHAR, VARBINARY, BLOB, or TEXT columns). #Heidisql mysql optimizer archive#OPTIMIZE TABLE works for InnoDB (before MariaDB 10.1.1, only if the innodb_file_per_table server system variable is set), Aria, MyISAM and ARCHIVE tables, and should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |