Constant WAL replay

We have toyed around with PostgreSQL's WAL structure and we are
wondering whether it is (theoretically) possible to replay WAL records
coming from a remote host while a system is working in read only mode.

The idea: We are looking for a way to implement a synchronous
single-master / multiple slaves systems.
Meanwhile we are able to serialize / deserialize WAL records and send
them to a group communication system which transports those records to
the slave database.
This is not hard to do. The problem is: How can we replay data on the
slave while the slave is answering read-only SQL-statements?

As far as I understand the code we can either recover the system or
answer SQL statements. Which kind of modifications are necessary to
replay and answer at the same time? (assuming that locks and
transactional information are available on the slave).

Input is very much appreciated.

Best regards,

Hans

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