LONDISTE(1)															       LONDISTE(1)

NAME

       londiste - PostgreSQL replication engine written in python

SYNOPSIS

       londiste.py [option] config.ini command [arguments]

DESCRIPTION

       Londiste is the PostgreSQL replication engine portion of the SkyTools suite, by Skype. This suite includes packages implementing specific
       replication tasks and/or solutions in layers, building upon each other.

       PgQ is a generic queue implementation based on ideas from Slony-I's snapshot based event batching. Londiste uses PgQ as its transport
       mechanism to implement a robust and easy to use replication solution.

       Londiste is an asynchronous master-slave(s) replication system. Asynchronous means that a transaction commited on the master is not
       guaranteed to have made it to any slave at the master's commit time; and master-slave means that data changes on slaves are not reported
       back to the master, it's the other way around only.

       The replication is trigger based, and you choose a set of tables to replicate from the provider to the subscriber(s). Any data changes
       occuring on the provider (in a replicated table) will fire the londiste trigger, which fills a queue of events for any subscriber(s) to
       care about.

       A replay process consumes the queue in batches, and applies all given changes to any subscriber(s). The initial replication step involves
       using the PostgreSQL's COPY command for efficient data loading.

QUICK-START
       Basic londiste setup and usage can be summarized by the following steps:

	1. create the subscriber database, with tables to replicate

	2. edit a londiste configuration file, say conf.ini, and a PgQ ticker configuration file, say ticker.ini

	3. install londiste on the provider and subscriber nodes. This step requires admin privileges on both provider and subscriber sides, and
	   both install commands can be run remotely:

	       $ londiste.py conf.ini provider install
	       $ londiste.py conf.ini subscriber install

	4. launch the PgQ ticker on the provider machine:

	       $ pgqadm.py -d ticker.ini ticker

	5. launch the londiste replay process:

	       $ londiste.py -d conf.ini replay

	6. add tables to replicate from the provider database:

	       $ londiste.py conf.ini provider add table1 table2 ...

	7. add tables to replicate to the subscriber database:

	       $ londiste.py conf.ini subscriber add table1 table2 ...

       To replicate to more than one subscriber database just repeat each of the described subscriber steps for each subscriber.

COMMANDS

       The londiste command is parsed globally, and has both options and subcommands. Some options are reserved to a subset of the commands, and
       others should be used without any command at all.

GENERAL OPTIONS

       This section presents options available to all and any londiste command.

       -h, --help
	   show this help message and exit

       -q, --quiet
	   make program silent

       -v, --verbose
	   make program more verbose

PROVIDER COMMANDS

	   $ londiste.py config.ini provider <command>

       Where command is one of:

   provider install
       Installs code into provider and subscriber database and creates queue. Equivalent to doing following by hand:

	   CREATE LANGUAGE plpgsql;
	   CREATE LANGUAGE plpython;
	   i .../contrib/txid.sql
	   i .../contrib/pgq.sql
	   i .../contrib/londiste.sql
	   select pgq.create_queue(queue name);

   provider add <table name> ...
       Registers table(s) on the provider database and adds the londiste trigger to the table(s) which will send events to the queue. Table names
       can be schema qualified with the schema name defaulting to public if not supplied.

       --all
	   Register all tables in provider database, except those that are under schemas pgq, londiste, information_schema or pg_*.

   provider remove <table name> ...
       Unregisters table(s) on the provider side and removes the londiste triggers from the table(s). The table removal event is also sent to the
       queue, so all subscribers unregister the table(s) on their end as well. Table names can be schema qualified with the schema name defaulting
       to public if not supplied.

   provider add-seq <sequence name> ...
       Registers a sequence on provider.

   provider remove-seq <sequence name> ...
       Unregisters a sequence on provider.

   provider tables
       Shows registered tables on provider side.

   provider seqs
       Shows registered sequences on provider side.

SUBSCRIBER COMMANDS

	   londiste.py config.ini subscriber <command>

       Where command is one of:

   subscriber install
       Installs code into subscriber database. Equivalent to doing following by hand:

	   CREATE LANGUAGE plpgsql;
	   i .../contrib/londiste.sql

       This will be done under the Postgres Londiste user, if the tables should be owned by someone else, it needs to be done by hand.

   subscriber add <table name> ...
       Registers table(s) on subscriber side. Table names can be schema qualified with the schema name defaulting to public if not supplied.

       Switches (optional):

       --all
	   Add all tables that are registered on provider to subscriber database

       --force
	   Ignore table structure differences.

       --expect-sync
	   Table is already synced by external means so initial COPY is unnecessary.

       --skip-truncate
	   When doing initial COPY, don't remove old data.

   subscriber remove <table name> ...
       Unregisters table(s) from subscriber. No events will be applied to the table anymore. Actual table will not be touched. Table names can be
       schema qualified with the schema name defaulting to public if not supplied.

   subscriber add-seq <sequence name> ...
       Registers a sequence on subscriber.

   subscriber remove-seq <sequence name> ...
       Unregisters a sequence on subscriber.

   subscriber resync <table name> ...
       Tags table(s) as "not synced". Later the replay process will notice this and launch copy process(es) to sync the table(s) again.

   subscriber tables
       Shows registered tables on the subscriber side, and the current state of each table. Possible state values are:

       NEW
	   the table has not yet been considered by londiste.

       in-copy
	   Full-table copy is in progress.

       catching-up
	   Table is copied, missing events are replayed on to it.

       wanna-sync:<tick-id>
	   The "copy" process catched up, wants to hand the table over to "replay".

       do-sync:<tick_id>
	   "replay" process is ready to accept it.

       ok
	   table is in sync.

   subscriber fkeys
       Show pending and active foreign keys on tables. Takes optional type argument - pending or active. If no argument is given, both types are
       shown.

       Pending foreign keys are those that were removed during COPY time but have not restored yet, The restore happens autmatically if both
       tables are synced.

   subscriber triggers
       Show pending and active triggers on tables. Takes optional type argument - pending or active. If no argument is given, both types are
       shown.

       Pending triggers keys are those that were removed during COPY time but have not restored yet, The restore of triggers does not happen
       autmatically, it needs to be done manually with restore-triggers command.

   subscriber restore-triggers <table name>
       Restores all pending triggers for single table. Optionally trigger name can be given as extra argument, then only that trigger is restored.

   subscriber register
       Register consumer on queue. This usually happens automatically when replay is launched, but

   subscriber unregister
       Unregister consumer from provider's queue. This should be done if you want to shut replication down.

REPLICATION COMMANDS

   replay
       The actual replication process. Should be run as daemon with -d switch, because it needs to be always running.

       It's main task is to get batches of events from PgQ and apply them to subscriber database.

       Switches:

       -d, --daemon
	   go background

       -r, --reload
	   reload config (send SIGHUP)

       -s, --stop
	   stop program safely (send SIGINT)

       -k, --kill
	   kill program immidiately (send SIGTERM)

UTILITY COMMAND

   repair <table name> ...
       Attempts to achieve a state where the table(s) is/are in sync, compares them, and writes out SQL statements that would fix differences.

       Syncing happens by locking provider tables against updates and then waiting until the replay process has applied all pending changes to
       subscriber database. As this is dangerous operation, it has a hardwired limit of 10 seconds for locking. If the replay process does not
       catch up in that time, the locks are released and the repair operation is cancelled.

       Comparing happens by dumping out the table contents of both sides, sorting them and then comparing line-by-line. As this is a CPU and
       memory-hungry operation, good practice is to run the repair command on a third machine to avoid consuming resources on either the provider
       or the subscriber.

   compare <table name> ...
       Syncs tables like repair, but just runs SELECT count(*) on both sides to get a little bit cheaper, but also less precise, way of checking
       if the tables are in sync.

CONFIGURATION

       Londiste and PgQ both use INI configuration files, your distribution of skytools include examples. You often just have to edit the database
       connection strings, namely db in PgQ ticker.ini and provider_db and subscriber_db in londiste conf.ini as well as logfile and pidfile to
       adapt to you system paths.

       See londiste(5).

SEE ALSO

       londiste(5)

       https://developer.skype.com/SkypeGarage/DbProjects/SkyTools/

       Reference guide[1]

NOTES

	1. Reference guide
	   http://skytools.projects.postgresql.org/doc/londiste.ref.html

								    03/13/2012							       LONDISTE(1)