Shulou(Shulou.com)06/01 Report--

This problem occurs when DELETE is followed by a condition.

Delete from table_name where condition

The size of the space occupied by the data table does not change after the data is deleted.

When you delete directly without following the conditions.

Delete from table_name

The data is cleared, and the space of the data table becomes 0

If a large portion of the table data has been deleted, or if many changes and variable length table rows (VARCHAR table, VARBINARY, BLOB, or text columns) have been changed, this is due to fragmentation in the data file after the delete operation. DELETE only deletes the data identity bits and does not collate the data files. When new data is inserted, the record space set to delete identification is used again. OPTIMIZE TABLE can be used to reclaim the unused space and defragment the data files.

OPTIMIZE TABLE only works on MyISAM, BDB, and InnoDB tables.

OPTIMIZE TABLE table name

For the myisam engine, using optimize table also has the following features:

If the table has deleted or split rows, repair the table. [repair table]

If the index pages are not sorted, sort them. [index not sorted, will be sorted]

If the table's statistics are not up to date (and the repair could not be accomplished by sorting the index), update them. [if the statistics of the table are not up to date, update it]

After the batch deletion of the myiam data table, it is found that the space is not reclaimed, and the space should be recycled through optimize table.

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