# "Choosing a Database on Zerops"


## Keywords
database, postgresql, mariadb, clickhouse, sql, relational, columnar, analytics, postgres, mysql, choose database, which database

## TL;DR
**Use PostgreSQL** for everything unless you have a specific reason not to. It's the best-supported database on Zerops with full HA, read replicas, and pgBouncer.

## Decision Matrix

| Need | Choice | Why |
|------|--------|-----|
| **General-purpose** | **PostgreSQL** (default) | Full HA, read replicas, pgBouncer, best Zerops support |
| MySQL compatibility | MariaDB | MaxScale routing, async replication |
| Analytics / OLAP | ClickHouse | Columnar storage, ReplicatedMergeTree, 4 protocol ports |

## PostgreSQL (Default Choice)

- HA: 3 nodes (1 primary + 2 replicas)
- Ports: 5432 (primary), 5433 (read replicas), 6432 (external TLS via pgBouncer)
- Connection: `postgresql://:@:5432/`
- Read scaling: Use port 5433 for read-heavy workloads

## MariaDB

- HA: MaxScale routing with async replication
- Port: 3306
- Connection: `mysql://:@:3306/`
- Use when: Application requires MySQL wire protocol

## ClickHouse

- HA: 3 data nodes, replication factor 3
- Ports: 9000 (native), 8123 (HTTP), 9004 (MySQL), 9005 (PostgreSQL)
- Requires `ReplicatedMergeTree` engine in HA mode
- Use when: Analytics, time-series, OLAP workloads

## Gotchas
1. **HA mode is immutable**: Cannot switch HA/NON_HA after creation — delete and recreate
2. **No internal TLS**: Use `http://hostname:port` internally — VPN provides encryption
3. **PostgreSQL URI scheme**: Some libraries need `postgres://` not `postgresql://` — create a custom env var

## See Also
- zerops://themes/services — PostgreSQL, MariaDB, ClickHouse service cards and wiring
- zerops://decisions/choose-cache