This is a package of tools in use in Skype for replication and failover. It also includes a generic queuing mechanism PgQ and utility library for Python scripts, as well as a script for setting up and managing WAL based standby servers.


It contains following modules:


PgQ is a queuing system written in PL/pgsql, Python and C code. It is based on snapshot based event handling ideas from Slony-I, written for general usage.

PgQ provides an efficient, transactionnal, queueing system with multi-nodes support (including work sharing and splitting, failover and switchover, for queues and for consumers).


  • There can be several queues in database.

  • There can be several producers than can insert into any queue.

  • There can be several consumers on one queue.

  • There can be several subconsumers on a consumer.

PgQ is splited into 3 layers: Producers, Ticker and Consumers.

Producers and Consumers respectively push and read events into a queue. Producers just need to call PostgreSQL stored procedures (like a trigger on a table or a PostgreSQL call from the application). And consumers are frequently written in Python, the prefered language as it has a powerful SKytools Framework but it is not limitative and any language able to run PostgreSQL stored procedures can be used.

Ticker is a daemon which splits the queues in batch of events and handle the maintenance of the system. The Ticker is provided with the Skytools.



Replication tool written in Python, using PgQ as event transport.


  • Tables can be added one-by-one into set.

  • Initial COPY for one table does not block event replay for other tables.

  • Can compare tables on both sides.


  • Londiste script usage: doc/londiste3.txt (also available as man 1 londiste)

  • Londiste HOWTOS: doc/howto/


This script will setup WAL archiving, does initial backup and runtime WAL archive and restore.

It can also be used for up-to-last-second partial file copying, so less than whole file is lost in case of loss of master database server.

Source tree contents


Documentation in asciidoc format. Source for both html and man pages.


Python modules and primary executables - walmgr, londiste, qadmin, pgqadm.


Python framework for PgQ.


Londiste replication.


Low-level utilities for writing database scripts in Python.


Database modules.


Table definitions and functions for PgQ queueing.


Framework for cascaded consuming.


Functions for cooperative consuming.


Table definitions and functions for Londiste replication.


PgQ ticker written in C.


Python scripts with lesser priority.


libusual C libary, for pgqd.


Debian packaging. This is for creating private packages, official Debian packages uses it’s own packagin code.


Random scripts used for building.

Upgrade from 2.1

Assuming PgQ + Londiste setup. This will upgrade PgQ to 3.0 and install Londiste 3 in parallel with Londiste 2.

  1. Install Postgres modules. They are backwards compatible with 2.1.

  2. Stop ticker processes.

  3. Apply ./upgrade/final/v3.0_pgq_core.sql

  4. Apply installed pgq_node.sql

  5. Apply installed londiste.sql - this will throw error on CREATE SCHEMA, but should otherwise apply fine.

  6. Start pgqd.