PostgreSQL extensibility is awesome. With things like extensions or custom worker backgrounds, there are many ways for a PostgreSQL developer to create modules without having to touch a single line of the core code at all. Among those tools, PostgreSQL contains a set of hooks that can be used to plug customized code at certain points of the server processing. Hooks are not documented at all, so if you want to know more about them you need either to have a look directly at the PostgreSQL code or to read the slides of the presentation about hooks given by Guillaume Lelarge at PGcon 2012. Personally I recommend the latter, Guillaume’s presentation being really good.

A new set of APIs for foreign data wrappers has been added to allow writable operations on foreign sources. This feature has been committed by Tom Lane a couple of days ago.

PostgreSQL 9.3 comes with a pretty cool feature called materialized views. It has been created by Kevin Grittner and committed by the same person not so long ago.

pg_xlogdump is a new contrib module introduced in PostgreSQL 9.3 by this commit.

Up to Postgres 9.2, the only foreign data wrapper present in core was file_fdw, allowing you to query files as remote tables. This has been corrected with the addition of a second foreign data wrapper called postgres_fdw. This one simply allows to query foreign Postgres servers and fetch results directly on your local server. It has been introduced by this commit.

pageinspect is an extension module of PostgreSQL core allowing to have a look at the contents of relations (index or table) in the database at a low level. In the case of PostgreSQL, tuples of a table are stored in blocks of data whose size can be changed with –with-blocksize at configure step. This module is particularly useful for debugging when implementing a new functionality that changes visibility of data like what could do an autovacuum or map visibility feature, or simply to understand the internals of Postgres without having to read much codea .

Based on my previous experience using custom background workers (new feature of PostgreSQL 9.3), here is more detailed example of bgworker doing a simple “Hello World” in the server logs.

PostgreSQL 9.3 adds a new feature related to monitoring with the commit below.

Prior to PostgreSQL 9.3, there are two levels of locks allowing to control DML operations on a given set of rows for a transaction by using SELECT FOR SHARE and FOR UPDATE. Such locks taken on rows in a transaction block allow blocking INSERT/DELETE/UPDATE on those rows. There is also a protocol between those lock levels. FOR UPDATE is equivalent to an exclusive lock on the row selected, meaning that no other backend can take a FOR UPDATE lock on the same row and waits until the other other transaction finishes. FOR SHARE means that all the other backends can take a FOR SHARE lock on those rows. No FOR UPDATE locks can be taken on rows already locked with FOR SHARE. It is also possible to use the NOWAIT option, making the server return an error if there is a wait situation.

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.