I run a small self-hosted observability tool on the cheapest VPS I could find on purpose: 2 cores, 2 GB RAM, 20 GB SATA SSD. It ingests errors, traces and metrics from two low-traffic sites of mine. The stack is three containers — a Go app, PostgreSQL, and ClickHouse.
One evening docker stats showed ClickHouse sitting on 880 MB of its 1 GB limit and the box swapping, with basically zero events coming in. So I went looking for where the memory and disk had gone. The answer turned out to be a good lesson in how a database can spend almost all of its I/O talking to itself.
543 KB of my data, 579 MB of ClickHouse talking about ClickHouse
First thing I checked: how much data had my app actually stored versus how much ClickHouse had stored about itself.
My application database: 543 KB, 16k rows
