Why does truncate take so long?
Using TRUNCATE TABLE on an InnoDB table requires a full table lock because TRUNCATE TABLE is DDL (Data Definition Language) not DML (Data Manipulation).
Doing DELETE FROM user_engagements; will not help because MVCC info is written to the undo logs in ibdata1, and that can hold up the table from being emptied ….
Can we rollback truncate?
You cannot ROLLBACK TRUNCATE Simply, you cannot rollback a transaction if it is already committed but you can do something else to get the data back (or at least some parts of it). When you execute the TRUNCATE statement, your data is still in the MDF file.
Does truncate free space?
If you’re using innodb_file_per_table=ON, or you’re using MyISAM, TRUNCATE TABLE will delete the table files used by the table in question (and create new, empty ones). So, the space used will be released to the file system, and in Unix/Linux, “df” on the file system will show new space.
Is truncate DDL or DML?
Although TRUNCATE TABLE is similar to DELETE , it is classified as a DDL statement rather than a DML statement. It differs from DELETE in the following ways: Truncate operations drop and re-create the table, which is much faster than deleting rows one by one, particularly for large tables.
How fast is truncate table?
A millisecond or so. Truncate is O(1) – a pure metadata operation. This is assuming there is no concurrent activity on the table.
What are 2 differences between delete and truncate?
Everyone should know that DELETE is DML command and TRUNCATE is DDL command. DELETE deletes records one by one and makes an entry for each and every deletion in the transaction log, whereas TRUNCATE de-allocates pages and makes an entry for de-allocation of pages in the transaction log.
How do I rollback in SQL?
You can see that the syntax of the rollback SQL statement is simple. You just have to write the statement ROLLBACK TRANSACTION, followed by the name of the transaction that you want to rollback.
Can truncate have where condition?
TRUNCATE cannot be executed with a WHERE clause means that all records will be removed from the TRUNCATE / statement. However, partitions can be truncated as shown in the below T-SQL statement. From the above statement, partitions 2,4,6,7,8 will be truncated leaving the other partitions data will not be truncated.
What is the difference between drop and truncate?
DROP is a DDL Command. Objects deleted using DROP are permanently lost and it cannot be rolled back. Unlike TRUNCATE which only deletes the data of the tables, the DROP command deletes the data of the table as well as removes the entire schema/structure of the table from the database.