SKs should only get changed if you re updating a portion of the key itself or a portion of the PK that it refers back to. In most tree oriented storage engines this results in a deletion of the record in the effected SKs and a re-insertion of the record as the position of the record within the tree will have changed.

Let’s say I use auto-increment as the primary key. My understanding is that in innoDB updates are in-place so each row has an auto-increment id that doesn’t change. Secondary indexes simply point to this auto-increment id.

In RocksDB updates are not in-place but result in new versions of the row. Do these different versions all share the same auto-increment id? If not does that mean each update would change the primary key of the newest version to a new auto-increment id? In that case would the secondary indexes need to be updated to point to the newest primary key? If I have 20 indexes that’s a lot of updates to be done for simply changing 1 row.