Mastering Stateful Stream Reordering at 200,000 Messages per Second
Cisco, Wednesday, November 4th, 2026
Cisco engineers describe replacing RocksDB-backed reordering in an Apache Flink job with an in-memory buffer at 200,000 messages per second.
A Cisco DevNet post explains how a team processing network connection events from Kafka needed to reorder each session's steps, such as auth, assoc, dhcp and dns, into event-time order to judge connection success.
At 200,000 messages per second, bursty and late traffic caused the original Flink application to produce false positives in success reporting.
The team found the bottleneck with Flink's flame graph and rebuilt the reordering logic as an in-memory buffer, taking RocksDB off the hot path.
They ran the new version beside the original on production data for five months using an A/B development pattern, then cut over by changing default topics.