Because of its disk layout, Cassandra is truly excellent at time-series, append-heavy data. In our setup, the data is partitioned by time bucket and n number of labels (one of which is the request ID).

We may unify the two at some point, but there's no immediate need to do so. While the write use-case is quite similar across both, the read use-case is quite different: slog requires reasonably low latency reads soon after the data is written, data can age out after 2-30 days depending on severity, and sometimes dropping events is acceptable. It would be acceptable for reads from the "archival" system to take minutes or even hours, the data should be kept forever (or for a long time), and dropping events is never acceptable.