ETL vs ELT
ETL cleans the data before it loads. ELT loads the raw data and cleans it inside the warehouse. Raw events arrive at 60 MB/s, but the warehouse loads at most 50 MB/s, and dashboards need only 4 percent of the data. ELT fails with p99 over 10 s and 5.9 percent errors. ETL passes with p99 14 ms.
2 workers · 1 TB moves in 1.1 h · 1,000 Mbps per card
Case 1
Raw JSON events arrive at 60 MB/s. Dashboards need only the 4 percent that survives cleaning. The warehouse loads at most 50 MB/s. Shop p99 must stay below 50 ms and no event may be lost.
| Measure | Goal | ETL: clean, then load | ELT: load, then clean |
|---|---|---|---|
| p99 latency (Shop) | under 50 ms | 3.3 ms Pass | 3.3 ms Pass |
| p99 latency (Raw) | under 2 s | 14 ms Pass | 10.1 s Fail |
| Error rate (Raw) | under 0.1% | 0% Pass | 5.9% Fail |
| Monthly cost | 160 USD/mo | 128 USD/mo |