so, when do you actually make the switch from SQL to NoSQL?

our relational database is gettin slow, like, queries are a nightmare and load times are gettin longer. prob gonna switch to NoSQL but its a big move and kinda scary. when do you guys know its time to switch to NoSQL tho. like what kind of data or queries make you say 'yep, NoSQL time'. wanna hear how youve dealt with this.