NAME

       pgqadm - PgQ ticker and administration interface

SYNOPSIS

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

DESCRIPTION

       PgQ is Postgres based event processing system. It is part of SkyTools package that
       contains several useful implementations on this engine. Main function of PgQadm is to
       maintain and keep healthy both pgq internal tables and tables that store events.

       SkyTools is scripting framework for Postgres databases written in Python that provides
       several utilities and implements common database handling logic.

       Event - atomic piece of data created by Producers. In PgQ event is one record in one of
       tables that services that queue. Event record contains some system fields for PgQ and
       several data fileds filled by Producers. PgQ is neither checking nor enforcing event type.
       Event type is someting that consumer and produser must agree on. PgQ guarantees that each
       event is seen at least once but it is up to consumer to make sure that event is processed
       no more than once if that is needed.

       Batch - PgQ is designed for efficiency and high throughput so events are grouped into
       batches for bulk processing. Creating these batches is one of main tasks of PgQadm and
       there are several parameters for each queue that can be use to tune size and frequency of
       batches. Consumerss receive events in these batches and depending on business requirements
       process events separately or also in batches.

       Queue - Event are stored in queue tables i.e queues. Several producers can write into same
       queeu and several consumers can read from the queue. Events are kept in queue until all
       the consumers have seen them. We use table rotation to decrease hard disk io. Queue can
       contain any number of event types it is up to Producer and Consumer to agree on what types
       of events are passed and how they are encoded For example Londiste producer side can
       produce events for more tables tan consumer side needs so consumer subscribes only to
       those tables it needs and events for other tables are ignores.

       Producer - applicatione that pushes event into queue. Prodecer can be written in any
       langaage that is able to run stored procedures in Postgres.

       Consumer - application that reads events from queue. Consumers can be written in any
       language that can interact with Postgres. SkyTools package contains several useful
       consumers written in Python that can be used as they are or as good starting points to
       write more complex consumers.

QUICK-START

       Basic PgQ setup and usage can be summarized by the following steps:

        1. create the database

        2. edit a PgQ ticker configuration file, say ticker.ini

        3. install PgQ internal tables

               $ pgqadm.py ticker.ini install

        4. launch the PgQ ticker on databse machine as daemon

               $ pgqadm.py -d ticker.ini ticker

        5. create queue

               $ pgqadm.py ticker.ini create <queue>

        6. register or run consumer to register it automatically

               $ pgqadm.py ticker.ini register <queue> <consumer>

        7. start producing events

CONFIG

           [pgqadm]
           job_name = pgqadm_somedb

           db = dbname=somedb

           # how often to run maintenance [seconds]
           maint_delay = 600

           # how often to check for activity [seconds]
           loop_delay = 0.1

           logfile = ~/log/%(job_name)s.log
           pidfile = ~/pid/%(job_name)s.pid

COMMANDS

   ticker
       Start ticking & maintenance process. Usually run as daemon with -d option. Must be running
       for PgQ to be functional and for consumers to see any events.

   status
       Show overview of registered queues and consumers and queue health. This command is used
       when you want to know what is happening inside PgQ.

   install
       Installs PgQ schema into database from config file.

   create <queue>
       Create queue tables into pgq schema. As soon as queue is created producers can start
       inserting events into it. But you must be aware that if there are no consumers on the
       queue the events are lost until consumer is registered.

   drop <queue>
       Drop queue and all it’s consumers from PgQ. Queue tables are dropped and all the contents
       are lost forever so use with care as with most drop commands.

   register <queue> <consumer>
       Register given consumer to listen to given queue. First batch seen by this consumer is the
       one completed after registration. Registration happens automatically when consumer is run
       first time so using this command is optional but may be needed when producers start
       producing events before consumer can be run.

   unregister <queue> <consumer>
       Removes consumer from given queue. Note consumer must be stopped before issuing this
       command otherwise it automatically registers again.

   config [<queue> [<variable>=<value> ... ]]
       Show or change queue config. There are several parameters that can be set for each queue
       shown here with default values:

       queue_ticker_max_lag (2)
           If no tick has happend during given number of seconds then one is generated just to
           keep queue lag in control. It may be increased if there is no need to deliver events
           fast. Not much room to decrease it :)

       queue_ticker_max_count (200)
           Threshold number of events in filling batch that triggers tick. Can be increased to
           encourage PgQ to create larger batches or decreased to encourage faster ticking with
           smaller batches.

       queue_ticker_idle_period (60)
           Number of seconds that can pass without ticking if no events are coming to queue.
           These empty ticks are used as keep alive signals for batch jobs and monitoring.

       queue_rotation_period (2 hours)
           Interval of time that may pass before PgQ tries to rotate tables to free up space. Not
           PgQ can not rotate tables if there are long transactions in database like VACUUM or
           pg_dump. May be decreased if low on disk space or increased to keep longer history of
           old events. To small values might affect performance badly because postgres tends to
           do seq scans on small tables. Too big values may waste disk space.

       Looking at queue config.

           $ pgqadm.py mydb.ini config
           testqueue
               queue_ticker_max_lag        =     3
               queue_ticker_max_count      =   500
               queue_ticker_idle_period    =    60
               queue_rotation_period       =  7200
           $ pgqadm.py conf/pgqadm_myprovider.ini config testqueue queue_ticker_max_lag=10 queue_ticker_max_count=300
           Change queue bazqueue config to: queue_ticker_max_lag='10', queue_ticker_max_count='300'
           $

COMMON OPTIONS

       -h, --help
           show help message

       -q, --quiet
           make program silent

       -v, --verbose
           make program verbose

       -d, --daemon
           go background

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

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

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

                                            03/13/2012                                  PGQADM(1)