Small clarification: > If you specify ALGORITHM=INPLACE,LOCK=NONE you can alter table without blocking reads and writes. We have used this method successfully

Small clarification: > If you specify ALGORITHM=INPLACE,LOCK=NONE you can alter table without blocking reads and writes. We have used this method successfully in Amazon RDS when updating schemas. The use-case of ALGORITHM=INPLACE and LOCK=NONE is to produce an error if the modification you are attempting is not supported in this mode. i.e. even if you don't specify LOCK=NONE, that doesn't mean it will lock. This is useful in preventing guessing games (i.e. you think its LOCK=NONE, but for some reason it's not compatible...)