I want to be able to track changes to records in a PostgreSQL database. I’ve considered using a version field and on-update rules or triggers such that previous versions of records are kept in the table (or in a separate table). This would have the advantage of making it possible to view the version history of a record with a simple select statement. However, this functionality is something I think likely to be seldom used.
How could I satisfy the requirement of being able to construct a “version history” for a record using the WAL files? Reading the WAL and Point-in-Time recovery documentation at PostgreSQL.org has helped me understand how the state of the entire database can be rolled back to an arbitrary point in time, but not how to deal with update mistakes in particular records.
No, you cannot do this at this time. There is a large effort underway on the postgresql-hackers mailing list (the dev list) to rework WAL and build an interface to allow for logical replication in (possibly) PostgreSQL 9.3.
This is basically what you appear to be trying to do and, based on the discussions on that list, it is definitely not a trivial task.