After a rolling restart of our Kafka cluster, the warehouse system was missing about 300 order events the producer had logged as sent. The producer used acks=1, so the leader acknowledged before followers had the data. How we proved it, and the settings that make acknowledged writes durable.
After saving their profile, some users saw the old values on the next page and saved again. Laravel's sticky option only covers a single request, and the redirect read from a replica that was seconds behind. We fixed it with a WAL position check.
Most Kafka incidents we get paged for come down to five concepts: partitions, leaders, the in-sync replica set, producer acks and consumer group assignment. This is the mental model we use to read the symptoms and find the cause fast.
Postgres and MySQL both speak SQL, but their internals push applications in different directions. We compare connections, MVCC and cleanup, clustered versus heap storage, and replication, and list what each difference changes in your code and operations.
Our MySQL primary hung and then aborted with the data volume at 100%. Binary logs had grown to 410 GB because a backfill tripled write volume while retention had been raised for a lagging replica. How we recovered, purged safely and stopped it recurring.
Replication, partitioning and sharding solve different problems, and picking the wrong one buys complexity without relief. This guide starts from the bottleneck you can measure and walks to the option that fixes it, including when Citus is worth it.