As subjects, what will happen to the backup file while there is still many active transaction in the database. Does it export realtime or just partially backups ?
thanks in advance.
pg_dump runs in a serializable transaction, so it sees a consistent snapshot of the database including system catalogs.
However it is possible to get 'cache lookup failed' error if someone performs DDL changes while a dump is starting. The time window for this sort of thing isn't very large, but it can happen. See: http://archives.postgresql.org/pgsql-bugs/2010-02/msg00187.php
pg_dump will give you a consistent state. Any transaction not completed before pg_dump has been issued will not be reflected.
来源：https://stackoverflow.com/questions/3995646/doing-pg-dump-while-still-many-active-transaction