How to Use Event Triggers in ParadeDB

Galaxy Glossary

How do I create and manage event triggers in ParadeDB?

Event triggers automatically run a user-defined function when specified DDL events occur in ParadeDB.

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Description

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What problem do ParadeDB event triggers solve?

Event triggers let you react instantly to DDL changes—such as CREATE TABLE or ALTER FUNCTION—without polling or manual scripts. They help enforce standards, capture audit logs, or regenerate dependent objects.

How do event triggers differ from regular triggers?

Regular triggers fire on data changes in a single table, while event triggers fire on global catalog events.They operate at the database level and can inspect multiple affected objects through helper functions.

When should I use event triggers in an ecommerce schema?

Use them to: (1) log every schema change to an audit_ddl table; (2) block unapproved DROP TABLE on critical tables like Orders; (3) refresh materialized views after bulk DDL migrations.

How do I create an event trigger?

First, create a SECURITY DEFINER function returning event_trigger. Then attach it with CREATE EVENT TRIGGER.The trigger fires on events you specify, such as ddl_command_end or sql_drop.

Syntax breakdown

CREATE EVENT TRIGGER needs a name, event, optional filters, and the function to call. ParadeDB inherits PostgreSQL options like WHEN TAG IN (...) for granular filtering.

How can I view existing event triggers?

Query pg_event_trigger or run \dy in psql/Galaxy.This shows trigger names, events, and attached functions, enabling quick audits of active hooks.

How do I alter or drop an event trigger?

Disable with ALTER EVENT TRIGGER trigger_name DISABLE; or remove entirely using DROP EVENT TRIGGER trigger_name;. Always test in staging to avoid accidental production outages.

What are best practices for ParadeDB event triggers?

1. Keep functions lightweight—write to an async queue if heavy work is needed. 2. Use SECURITY DEFINER and set proper ownership. 3.Version-control both trigger and function DDL.

What common mistakes should I avoid?

See dedicated section below for typical pitfalls like forgetting catalog helper calls and mis-scoping filters.

Summary: Why master event triggers?

Event triggers are powerful automation hooks. When used carefully, they improve auditability and governance in ParadeDB-backed applications while reducing manual overhead.

Why How to Use Event Triggers in ParadeDB is important

How to Use Event Triggers in ParadeDB Example Usage


-- Block unwanted DROP TABLE on critical ecommerce tables
CREATE FUNCTION prevent_drop_orders() RETURNS event_trigger
LANGUAGE plpgsql SECURITY DEFINER AS $$
BEGIN
  IF EXISTS (
    SELECT 1 FROM pg_event_trigger_dropped_objects()
    WHERE objtype = 'table' AND object_name = 'orders') THEN
      RAISE EXCEPTION 'Dropping Orders table is forbidden!';
  END IF;
END;$$;

CREATE EVENT TRIGGER stop_drop_orders
ON sql_drop
WHEN TAG IN ('DROP TABLE')
EXECUTE FUNCTION prevent_drop_orders();

How to Use Event Triggers in ParadeDB Syntax


CREATE FUNCTION log_ddl() RETURNS event_trigger
LANGUAGE plpgsql SECURITY DEFINER AS $$
BEGIN
  INSERT INTO audit_ddl(action, object_type, object_name, executed_at)
  SELECT tg_tag, objtype, objid::regclass::text, NOW()
  FROM pg_event_trigger_dropped_objects();
END;$$;

CREATE EVENT TRIGGER trg_log_ddl
ON sql_drop
EXECUTE FUNCTION log_ddl();

Common Mistakes

Not calling catalog helper functions: Developers often forget to use pg_event_trigger_ddl_commands() or pg_event_trigger_dropped_objects(), leaving the trigger with no context. Always fetch details inside the trigger body to know which objects fired the event.
Running heavy logic inline: Performing long-running ETL inside an event trigger blocks DDL completion. Offload heavy work to background jobs or LISTEN/NOTIFY to keep migrations fast.

Frequently Asked Questions (FAQs)

Can event triggers fire on data changes?

No. They only respond to DDL events. Use table triggers for INSERT/UPDATE/DELETE operations.

Do event triggers run in transaction blocks?

Yes. If the surrounding transaction rolls back, changes made inside the trigger also roll back unless you use autonomous transactions via dblink or background workers.

Are event triggers replicated?

Triggers themselves are schema objects and replicate via logical replication. Their side effects execute on the subscriber if the function exists there.