Zemi

Zemi is an automatic PostgreSQL change tracking system. It connects to your database's Write-Ahead Log (WAL) and captures every data change (INSERT, UPDATE, DELETE, TRUNCATE) in real-time, persisting them to a queryable changes table.

A from-scratch rewrite of Bemi in Zig, Zemi replaces the original multi-runtime architecture (Java/Debezium + Go/NATS + TypeScript/Node.js) with a single statically-linked binary.

At a Glance

Metric	Original Bemi	Zemi	Improvement
Docker image	3.23 GB	1.04 MB	3,100x smaller
Memory (RSS)	300-500+ MB	2.8 MB	~150x less
Startup time	30-60 seconds	<1 ms	instant
Throughput	~97 changes/s	~2,000 changes/s	~20x faster
Latency (p50)	~977 ms	~75 ms	~13x faster
Processes	4+	1	single process

See Benchmarks for full details.

Quick Start

Docker

docker run --rm \
  -e DB_HOST=host.docker.internal \
  -e DB_PORT=5432 \
  -e DB_NAME=mydb \
  -e DB_USER=postgres \
  -e DB_PASSWORD=secret \
  ghcr.io/deanmarano/zemi:latest

From Source

# Requires Zig 0.14.1 (or use: asdf install)
zig build
DB_HOST=127.0.0.1 DB_NAME=mydb DB_USER=postgres DB_PASSWORD=secret ./zig-out/bin/zemi

Pre-built Binaries

Download from GitHub Releases:

Binary	Platform	Size
zemi-x86_64-linux	Linux x86_64 (static)	3.7 MB
zemi-aarch64-linux	Linux ARM64 (static)	3.8 MB
zemi-x86_64-macos	macOS Intel	510 KB
zemi-aarch64-macos	macOS Apple Silicon	497 KB

Prerequisites

PostgreSQL 14+ with logical replication enabled:

ALTER SYSTEM SET wal_level = logical;
-- Restart PostgreSQL after this change

See the hosting platform guides for provider-specific instructions (AWS RDS, Supabase, Neon, etc.).

To track both "before" and "after" states on data changes:

ALTER TABLE [tracked_table_name] REPLICA IDENTITY FULL;

How It Works

1. Zemi connects to PostgreSQL's logical replication stream
2. It decodes WAL changes using the pgoutput plugin
3. If your app uses a supported ORM package, application context (user ID, request ID, etc.) is automatically stitched onto each change
4. Changes are persisted to a changes table in the destination database

PostgreSQL WAL --> zemi (single binary) --> PostgreSQL (changes table)

See Architecture for the full technical deep-dive.

Use Cases

• Audit Trails -- compliance logs for customer support and external customers
• Time Travel -- retrieve historical data without event sourcing
• Troubleshooting -- identify root causes of application issues
• Change Reversion -- revert changes or rollback API request side effects
• Distributed Tracing -- track changes across distributed systems
• Trend Analysis -- gain insights into historical data changes

Supported ORM Packages

Zemi is fully compatible with all Bemi ORM packages for automatic context stitching:

JavaScript/TypeScript

• Prisma
• Drizzle
• TypeORM
• Supabase JS
• MikroORM

Ruby

• Ruby on Rails

Python

• SQLAlchemy
• Django

Changes Table Schema

Column	Type	Description
id	uuid	Unique change identifier
database	text	Source database name
schema	text	Source schema name
table	text	Source table name
operation	text	INSERT, UPDATE, DELETE, or TRUNCATE
before	jsonb	Row state before the change (null for INSERT)
after	jsonb	Row state after the change (null for DELETE)
context	jsonb	Application context (from ORM packages)
primary_key	text	Primary key value
committed_at	timestamptz	Transaction commit time
position	bigint	WAL position (LSN as numeric)
queued_at	timestamptz	Time the change was queued
created_at	timestamptz	Time the change was persisted

This schema is identical to the original Bemi -- existing queries work without modification.

Migrating from Bemi?

Zemi is a drop-in replacement. See the Migration Guide.