Continuing with the new features planned for PostgreSQL 9.3, here are some explanations about a new COPY mode called FREEZE. This feature has been introduced by this commit.

A new feature ideal for module makers is appearing in Postgres 9.3. Called “background worker processes”, this feature, which is a set of useful APIs, offers the possibility to create and customize worker processes called bgworkers able to run user-specified code directly plugged in the server. This worker is loaded and managed entirely by the server. So such processes can be considered as envelopped in a wrapper on top of the core code as a plug-in.

Prior to PostgreSQL 9.3, trying to execute a DML on a view results in an error. The view is not able to execute directly a query to its parent table. For example, you can see this kind of behavior in 9.2.

Since PostgreSQL 9.1, it is possible to switch a standby server to follow another server that has been freshly promoted after the master node of a cluster is out due to a failure (disaster or another). In this example, a master and two slaves are running on the same machine. The master running with port 5432 fails, Slave 1 is promoted as the new master:

A foreign-data wrapper (FWD) in a Postgres server allows to fetch data from an foreign entity or a foreign server. In this case, the Postgres planner and executer have the notion of what is called a foreign scan, which can be called using customized routines and fetch data that is not directly stored inside the Postgres server itself.

pg_buffercache is a PostgreSQL contrib module allowing to get an instant relation-based view of the shared buffer usage by querying the wanted server.

One of the new features introduced by PostgreSQL 9.2 is called range types, which is, as you could easily guess based on this feature name, the possibility to use a range of values directly as a table column.

hstore is a PostgreSQL contrib module in core code for a pretty long time. Its code is located in contrib/hstore in source folder. It is particularly useful to store sets of key/value in a single table column.

PostgreSQL 9.2 has introduced a new feature related to JSON with a built-in data type. So you can now store inside your database directly JSON fields without the need of an external format checker as it is now directly inside Postgres core. The feature has been added by this commit.

Last week, I had an interesting discussion in the Postgres hackers mailing list about integrating pg_reorg features (possibility to reorganize a table without locks on it) directly into postgres core. Community strongly suggested that pg_reorg cannot be integrated as-is in the contribution modules of postgres core, and instead postgres should provide native ways to reorganize a table without taking heavy locks. This means that a table could be reindexed or clustered, and at the same time read and writes operations could still happen in parallel. What is particularly useful when an index is broken in a production database, as you could keep your table free of access for the other sessions running while the table is reorganized.