Non-CDB database vs Single tenant CDB

To answer your second question first: yes you should partition. Oracle's query optimizer has a feature called partition elimination, which will check the predicate for the partition and only execute the SQL on the appropriate partitions.

Partitioning also leaves all the data in one space. Conceptually, think of it as many tables of identical structure, with an implicit UNION ALL between them if you were to do a SELECT from the entire table. Except "under the hood" Oracle sorts the actual rows into the right "table" based on the criteria you specify. Any rows that come in that don't match any of the criteria, go into what's known as the "default" partition.

For what you want to do, a "range partition" might be a good approach (so you can add more tenants later), e.g.:

create table transaction (id, tenant_id, a, b, c, d)
partition by range(tenant_id)
partition p_tenant1 values less than (2) tablespace ts_tenant1
partition p_tenant2 values less than (3) tablespace ts_tenant2
partition p_tenant3 values less than (4) tablespace ts_tenant3
partition p_tenantd values less than (MAXVALUE) tablespace ts_default;

Then later

alter table transaction 
add partition p_tenant4 values less than (5) tablespace ts_tenant4;

This will create something that looks and behaves just like a normal table, but actually rows where tenant_id=1 will be in a partition in tablespace ts_tenant1, and queries will ignore all other partitions. Queries across the entire table can run in parallel on each partition. If tenant_id=4 in this scenario, the row will live in ts_default unless you add the new partition as shown, but the INSERT won't be rejected because there's no partition for it!

FWIW At my site we use partitioned tables in our 40Tb DW, you don't need to worry about this approach scaling or performing, if you choose your partitioning strategy well (e.g. you could partition on tenant_id then subpartition on month perhaps), create the right indexes, and so on.

Based on Phil's test case I backed up the the production database using exp.

I dropped the editioned user, recreated them and imported the data with no issues. The user had views and packages which were versioned but as long as you set the edition to the most current one you are good to go.

This query showed that the recreated user was not using editioning

SELECT username,editions_enabled
FROM   dba_users
WHERE editions_enabled = 'Y';