Resetting AUTO_INCREMENT is taking a long time in MySQL

Question

ALTER TABLE tablename AUTO_INCREMENT = 10000000

This query is taking long time to update. Why? I need to optimize this query.

Answer 1

ALTER TABLE causes a rebuild of the entire table - if your table contains many rows,this can take ages.

If you just need to bump up the value of the auto_increment value, the quickest way is to insert a dummy row (and then delete that roow if need be). This will only take a fraction of a second, whereas ALTER TABLE can take days for a large table.

For example, suppose I have a table with an auto_increment ID column and other columns col1, col2...:

insert into autoinc_table set ID = 10000000;
delete from autoinc_table where ID = 10000000;