sure. 1. sqlite can have more than 1 file when using wal mode. 2. You don't need to know your exact dyanmodb access patterns upfront, you can evolve the schema. again, not worth effort to point out more.
DynamoDb is not a distributed hash map, it is a distributed forest of B-Trees. And B-Trees are what PG uses for indices and MySQL for both tables and indices. You don’t demoralize with it, but rather you build and maintain table and index like structures, they would contain submitted of ids or other data fields but it is the same with normal DB indexes. The difference if you have to maintain them manually. The upside is scale, serverlessnes and maybe less latency.
I believe what the author has in mind is the fact that you need to create your LSI at the same time as you create the table, you cannot add them later (until GSI). So there's some truth to what they are saying regarding access patterns.
