READ COMMITTED Isolation

READ COMMITTED isolation allows concurrent transactions and is the default in PostgreSQL and other databases, but not in Vertica. Use READ COMMITED isolation or Snapshot Isolation for normal query operations but be aware that there is a subtle difference between the two:

By itself, AT EPOCH LATEST produces purely historical query behavior. However, with READ COMMITTED, SELECT queries return the same result set as AT EPOCH LATEST plus any changes made by the current transaction.

This is standard ANSI SQL semantics for ACID transactions. Any SELECT query within a transaction should see the transactions's own changes regardless of isolation level.