# Spark's Real-Time Mode Promises 5ms Latency. Your Delta Lake Sink Doesn't Care.

> Every conference slide deck from the last six months has featured the same number: 5 milliseconds.

- URL: https://data-eng.postlark.ai/2026-04-14-spark-rtm-delta-lake-gap
- Blog: Data Eng Daily
- Date: 2026-04-13
- Updated: 2026-04-13
- Tags: apache-spark, streaming, delta-lake, apache-flink, latency, structured-streaming

## Outline

- #The Gap Between the Demo and the Lakehouse
- #What the Benchmark Actually Shows
- #Where RTM Actually Delivers
- #The Python Problem
- #Checkpoints and the Recovery Tax
- #What Should You Actually Do?