Replication slots can be used in streaming replication, with physical replication slots, and logical decoding, with logical replication slots, to retain WAL in a more precise way than wal_keep_segments so as past WAL segments are removed at checkpoint using the WAL position a client consuming the slot sees fit. A feature related to replication slots has been committed to PostgreSQL 12:

PostgreSQL 12 has changed the way recovery configuration works, and has introduced a couple of incompatible issues as mentioned in the main commit which has done the switch:

Since Postgres 11, it is possible to monitor progress activity of running manual VACUUM and even autovacuum using a dedicated system catalog called pg_stat_progress_vacuum. This is vital for operators when doing some long-running operations, because it is possible to not blindly wait for an operation to finish. When doing performance workload analysis, this is also proving to be helpful in evaluating VACUUM job progressing for tuning system-level parameters or even relation-level once depending on the load pattern.

Postgres ships in-core data types for JSON with specific functions and operators (json since 9.2, and jsonb which is a binary representation since 9.4). The upcoming Postgres 12 is becoming more compliant with the SQL specifications by introducing SQL/JSON path language, introduced mainly by the following commit:

Postgres is very nice when it comes to extending with custom plugins, with many set of facilities available, like:

A lot of work has been put into making Postgres 12 an excellent release to come, and in some of the features introduced, there is one which found its way into the tree and has been first proposed to community at the end of 2012. Here is the commit which has introduced it:

pg_checksums is a renaming of the tool called pg_verify_checksums which has been introduced in Postgres 11. Version 12 is introducing new options and possibilities which explain the renaming, as the tool has become much more multi-purpose.

The maximum number of connections a PostgreSQL can accept is configured using max_connections. When attempting to connect to a server already at full capacity, logically the server complains:

Postgres 12 is bringing a game-changer regarding common table expressions (named also CTE, defined by WITH clauses in SELECT queries) with the following commit:

Partitions in Postgres are a recent concept, being introduced as of version 10 and improved a lot over the last years. It is complicated, and doable, to gather information about them with specific queries working on the system catalogs, still these may not be straight-forward. For example, getting a full partition tree leads to the use of WITH RECURSIVE when working on partitions with multiple layers.