Re: Event-driven programming?

Hi

PgQ might be the answer for you.  Each transaction shouöd push event into queue and then you can write conusmers that notify each of the applications that need to react to this.

Extract from documentation:

PgQ is Postgres based event processing system. It is part of SkyTools package
that contains several useful implementations on this engine.

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.

regards,
Asko