v0.33.0 — Reactive Subscriptions & Zero-Downtime Operations

Full technical details: v0.33.0.md-full.md

Status: Planned | Scope: Medium

Live push notifications to applications, and a way to change a stream table’s defining query on a large production table without downtime.

What is this?

v0.33.0 adds two long-requested operational capabilities:

  1. Push notifications — applications can subscribe to changes in a stream table and receive instant notifications, enabling real-time dashboards, live UIs, and event-driven microservices.

  2. Zero-downtime query changes — modifying the defining query of a large stream table no longer requires a multi-minute lock on the table.

Reactive subscriptions

pgtrickle.subscribe('my_stream_table', 'my_notification_channel') registers a listener. After every successful refresh that produces at least one change, pg_trickle sends a PostgreSQL NOTIFY message to the named channel with a payload like:

{"name": "my_stream_table", "inserted_count": 12, "deleted_count": 3}

Any application holding a standard PostgreSQL connection and listening on that channel receives this signal immediately, without polling. This powers real-time dashboards, event-driven microservices, and reactive frontends — using nothing but a standard PostgreSQL driver, with no Kafka, no Debezium, no Hasura required.

A configurable coalescence window prevents notification storms when a stream table refreshes at high frequency.

Shadow-ST: zero-downtime query evolution

Today, calling alter_query() on a large stream table triggers a full re-computation of the entire result set. For a stream table with millions of rows, this can lock the table for minutes — an unacceptable operation in production.

The new shadow_build := true parameter to alter_query() changes how this works:

  1. A parallel “shadow” stream table is created from the new query, invisible to users.
  2. The shadow table is refreshed to convergence in the background, with no lock on the live table. The live table continues to serve reads and accept writes normally throughout.
  3. When the shadow table has caught up, the storage is swapped atomically.
  4. The new query goes live at the next refresh cycle. The shadow table is dropped.

The live table is readable and writable from start to finish.

Scope

v0.33.0 is a medium-sized release. The shadow-ST feature touches the refresh orchestrator — the most change-sensitive module in the codebase — and ships behind a feature flag with a full TPC-H validation pass before the flag is removed.

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