What are the disadvantages if indexes are added on all columns? I know, that it is not a good design to set too many indexes, but just for understanding the theory:
What exactly are the disadvantages if you add an index on all columns in a table in MySQL?


Are the queries getting slower if I have indexes on columns, that i
rarely use?
Are the inserts somewhat slower?
Is MySQL able to pick out the best index that speeds up the query?
Insert/Updates/Delete speed will degrade. The index has to be updated on data modification.
I don't know mysql in fine details but it also means more time spent by the query planner to determine the indexes to use.
More disk space.


These are the key disadvantages.