SQL/MX Queuing and Publish/Subscribe Services

Introduction
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Comparing Triggers and Publish/Subscribe
Comparing Triggers and Publish/Subscribe
SQL/MX Release 2.0 introduces triggers functionality. Both triggers and
publish/subscribe services offer ways to make a passive database more active. To
decide which feature to use (or whether to use both in the same application),
determine the needs of the application.
Table 1-1 compares triggers and publish/subscribe. For information about creating or
altering triggers, see the SQL/MX Reference Manual.
Table 1-1. Comparing Triggers and Publish/Subscribe (page 1 of 2)
Feature Triggers Publish/Subscribe
ANSI compliant? Yes. No.
Portable? Yes. No.
Action/timing The trigger action can occur
before or after an event.
The subscriber always
follows the publisher.
Supported on rows and
statements
You can have row triggers and
statement triggers.
The subscriber sees only
each row.
Event mechanism INSERT, UPDATE, or DELETE. INSERT and UPDATE.
Image of a row Triggers can see the before
and after image of each row.
The subscriber sees the
after image of a row (and
not necessarily all updates
to a row).
Transition variables Trigger actions can change
transition variables (change the
column values of the row
updated or inserted by the
triggering event).
The subscriber has no
access to the row until the
publisher commits.
Trigger action Triggers support the SIGNAL
statement, allowing an
operation to be disallowed and
the transaction to be rolled
back.
Publish/subscribe can
approximate this function
by using application logic to
undo the transaction.
Function Triggers are declarative. You
can declare a trigger as part of
a DDL statement. SQL/MX
enforces the triggers, making
them easy to manage.
Subscribers are procedural.
You have to write a
program to subscribe
against a given table. You
must also run (deploy and
manage) the program.
Transaction behavior The trigger event and action
occur in the same transaction
The publisher and
subscriber use different
transactions
Process usage Trigger actions are handled by
the same process as the
triggering event.
The publisher and
subscriber use different
processes.