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Re: Spec discussion: Generalized Data Queue / Modification Trigger

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Josh Berkus <josh(at)postgresql(dot)org>
Cc: PostgresCluster ML <pgsql-cluster-hackers(at)postgresql(dot)org>
Subject: Re: Spec discussion: Generalized Data Queue / Modification Trigger
Date: 2010-03-03 17:42:22
Message-ID: 4B8E9F7E.6060704@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-cluster-hackers
> Now, I have my idea on how I'd like the Data Queue / Modification
> Triggers to work, but I'm not the one who proposed those two closely
> related features.  Can the original proposers speak up on what kind of
> spec you had in mind?

Since nobody has spoken up about this, I'll spec it myself ...
particularly since I care strongly about it for heterogenous replication
(that is, replication to non-PostgreSQL systems).

As far as I can see, things would be of general utility:

(1) The ability to send asynchronous (or synchronous?) notifications, on
a per-row basis, whenever data is modified *only after commit*.  This
has been generally described as "on-commit triggers", but could actually
take a variety of forms.

(2) A generic yet compact portable serialization format for a row of
PostgreSQL data, just as protobuf, or something internal.

(3) A method of marking DDL changes in the data modification stream.

Of the three above, #2 seems the most optional, and possibly completely
counter-productive.  Even if we decided that a general portable data
format made sense, we could retrofit it later.  So dropping it from the
spec.

The question is, can we satisfy (1) with the new LISTEN/NOTIFY, or is it
inadequate?  I'll also point out that currently DEFFERABLE
CONSTRAINT/TRIGGERS can be perverted to work like an after-commit trigger.

For (3), it kind of depends on another item on the list, the DDL triggers.

Discussion?

--Josh Berkus


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