Replication slots is a new feature of PostgreSQL 9.4 that has been introduced by this commit:

When using COPY, there is an option called FORCE_NOT_NULL allowing to enforce a string to be not null even if it is not quoted. Here is an example of how it works:

PostgreSQL 9.4 is going to be shipped with a feature called ordered-set aggregates. This can be used with a new clause called WITHIN GROUP. All those things have been introduced by the following commit.

In PostgreSQL terminology, an LSN (Log Sequence Number) is a 64-bit integer used to determine a position in WAL (Write ahead log), used to preserve data integrity. Internally in code, it is managed as XLogRecPtr, a simple 64-bit integer. An LSN is represented with two hexadecimal numbers of 8 digits each separated with “/”. For example, when looking on server what is the current position of WAL, you can do something like that:

PostgreSQL 9.4 is going to be shipped with a feature of the SQL standard called WITH ORDINALITY. It has been introduced by this commit:

When writing an extension or module for PostgreSQL, having proper regressions tests and documentation are important things (with actually useful features!) to facilitate its acceptance.

The new foreign data wrapper available with PostgreSQL core called postgres_fdw (to basically query foreign Postgres servers and fetch back data locally) makes possible a couple of interesting things with a little bit of imagination. First, you need to be aware that postgres_fdw can query all types of relations on a remote server: not only tables but also materialized views, sequences (with SELECT * FROM seqname) and even views.

PostgreSQL 9.4 has added a new SQL command called ALTER SYSTEM SET, introduced by this commit:

When scanning a relation with a query with a bitmap heap scan and that the bitmap is not large enough to contain a reference to each tuple individually, bitmap heap scan switches to lossy mode where instead of the tuples relation pages are referenced in the bitmap. Then a Recheck condition on the heap is done to determine on each page which tuples to return, and to determine if a page is exact (tuples in the bitmap) or lossy (need to access to heap). The following commit adds an additional output in EXPLAIN ANALYZE to check the number of lossy and exact pages this bitmap heap scan used.

In PostgreSQL terminology, hint bints are a page-level mechanism implemented to be able to guess the visibility status of a tuple directly at the page level (actually whether the tuple xmin or xmax is committed or aborted), without going though checks in pg_clog and pg_subtrans which are expensive. This is part of the field t_infomask in HeapTupleHeaderData of htup_details.h, a set of bits telling about more or less the tuple status on a page.