from chatgpt

PostgreSQL
Strengths:
transactions, joins, constraints, flexible queries

Weaknesses:
horizontal scale/sharding complexity, not ideal for huge analytical scans

DynamoDB
Strengths:
massive scale, predictable low-latency key access, operational simplicity

Weaknesses:
access-pattern-driven modelling, limited relational querying

Columnar
Strengths:
analytical scans, aggregations, compression

Weaknesses:
poor fit for transactional workloads

Graph
Strengths:
relationship/traversal-heavy queries

Weaknesses:
specialised, unnecessary if relationships aren't the primary query pattern

Write heavy

In traditional database system with 1 master, it is difficult to scale writes.
A single postgres can manage well 5-10k write per second.

You can add more masters to distribute writes, but that's difficult to manage.
You can also use Database Sharding.