postgres: Database replica with some schemas writable
I'd use Londiste for this. Set up the data collector as a publisher and the analytics DB as a subscriber.

The main issue is that Londiste imposes a significant load due to write-amplification - each write must be written once to the table and once to a trigger-maintained replication queue. So using Londiste for replication may add too much load to an already struggling data collector server.



After comments: No PRIMARY KEY means you're pretty stuffed.

I haven't checked if any of the trigger based replication systems support append-only replication of tables without a PRIMARY KEY but I'd be surprised.

Streaming replication doesn't support replication of only some tables, nor is a replica writeable.

The only solution I know of that'll meet your use case is a unidirectional variant of BDR, which we're calling "UDR", but it's still a few months from being ready.