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= SkyTools - tools for PostgreSQL = This is a package of tools in use in Skype for replication and failover. It also includes a generic queuing mechanism called PgQ and a utility library for Python scripts, as well as a script for setting up and managing WAL based standby servers. == Overview == It contains the following modules: === PgQ === 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, and is written for general usage. PgQ provides an efficient, transactional, queueing system with multi-node support (including work sharing and splitting, failover and switchover, for queues and for consumers). Rules: - There can be several queues in a 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 split 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). Consumers are frequently written in Python (the preferred language as it has a powerful Skytools Framework), but are not limited to Python; any language able to run PostgreSQL stored procedures can be used. *Ticker* is a daemon which splits the queues into batchs of events and handle the maintenance of the system. The Ticker is provided with Skytools. Documentation: - PgQ ticker daemon (pgqd) usage: link:doc/pgqd.html - PgQ admin tool (qadm) usage: link:doc/qadmin.html - PgQ SQL API overview: link:doc/pgq-sql.html - PgQ SQL reference: link:pgq/ === Londiste === Replication tool written in Python, using PgQ as event transport. Features: - 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. Documentation: - Londiste script usage: doc/londiste3.txt (also available as `man 1 londiste`) - Londiste HOWTOS: doc/howto/ === walmgr === This script will setup WAL archiving, does the initial backup, and runtime WAL archive and restore. It can also be used for up-to-last-second partial file copying, so that less than the whole file is lost in case of loss of the master database server. == Source tree contents == doc/:: Documentation in asciidoc format. Source for both html and man pages. python/:: Python modules and primary executables - walmgr, londiste, qadmin, pgqadm. python/pgq/:: Python framework for PgQ. python/londiste/:: Londiste replication. python/skytools/:: Low-level utilities for writing database scripts in Python. sql/:: Database modules. sql/pgq/:: Table definitions and functions for PgQ queueing. sql/pgq_node/:: Framework for cascaded consuming. sql/pgq_coop/:: Functions for cooperative consuming. sql/londiste/:: Table definitions and functions for Londiste replication. sql/ticker/:: PgQ ticker written in C. scripts/:: Python scripts with lesser priority. lib/:: libusual C libary, for pgqd. debian/:: Debian packaging. This is for creating private packages, official Debian packages uses it's own packagin code. misc/:: 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 `pgqadm.py ticker` processes. 3. Apply pgq.upgrade_2.1_to_3.0.sql 3. Apply pgq.upgrade.sql 4. Apply pgq_node.sql 5. Apply londiste.sql - this will throw error on CREATE SCHEMA, but should otherwise apply fine. 6. Start pgqd. The files mentined above are installed under $PREFIX/share/skytools3/ directory.