ps_buckets - A small amount of metadata for each bucket.
ps_migrations - Table keeping track of SDK schema migrations.
Most rows will be present in at least two tables — the ps_data__<table> table, and in ps_oplog. It may be present multiple times in ps_oplog, if it was synced via multiple buckets.
The copy in ps_oplog may be newer than the one in ps_data__<table>. Only when a full checkpoint has been download, will the data be copied over to the individual tables. If multiple rows with the same table and id has been synced, only one will be preserved (the one with the highest op_id).