Question

I have a MyISAM table containing ~20 million rows, and need to increase the maximum size of a varchar. No matter how I phrase the ALTER TABLE query, it takes forever as MySQL copies all the data to a temporary table, reindexes it, etc – it seems to think that the data needs to be converted. Since it’s a varchar already, I’d have thought it wouldn’t need to do any of this.

Is there some way to force MySQL to increase the maximum length of a varchar without going through this horribly slow and painful process? I’m ideally looking for something which can be done entirely using SQL, so no trickery involving copying .frm files around etc.

Answer 1

One alternative would be to

1. create a copy of the table, but with the increased VARCHAR you need the table to be. BUT NO INDEXES.

2. Populate the new version of the table:

   INSERT INTO new_table
   SELECT * FROM old_table
   

3. Apply indexes
4. Update application references to use new_table

Step 4 can be minimized by updating the application to use a view that points to old_table until the new_table is ready. Then you refresh the view, setting it to use new_table…