Labs

Head-of-line blocking: log versus queue

Simulate 12 partitions with 100 records/s each and one poison record.

Per-record calls versus batches: find the natural batch size

Send 100,000 records to a local HTTP server in batches of 1 to 10,000 and fit the fixed cost per call.

Ack before or after processing: loss versus duplicates

Kill a consumer at random moments: saving the offset first loses records, processing first duplicates them.

Bufferbloat: a bigger buffer buys latency, not throughput

A producer 20% faster than its consumer, with queues from 100 to 100,000: throughput stays put, latency grows with the queue.

What an overflowing buffer loses

A keyed stream overloads a bounded buffer under drop-newest, drop-oldest and drop-oldest per key: count the records dropped and the entities left with a wrong value.

Batch size: find the knee

Insert 200,000 rows into SQLite with one commit per batch, then bound trickle-traffic latency with a size-or-age rule.

Token bucket versus fixed window

Two bursts straddling a one-second boundary against a fixed window, two token buckets and a sliding window.

Measure key skew and the effect of salting

Partition 1,000,000 events by seller, by order and by salted seller, when one seller owns 40% of them.

How many keys move when N changes? Modulo vs. ring vs. rendezvous

Add an eleventh node: how many of 100,000 keys move under modulo hashing, a ring with 1 or 128 virtual nodes, and rendezvous hashing.

Break per-key order in a real Kafka topic, then repair it

Per-key order in Kafka, broken three ways (a worker pool, lost acks without idempotence, growing the topic) and repaired twice.

A DLQ that does not become an outage amplifier

Write a small consumer with a retry-then-DLQ policy.

Choose N by measurement

Measure one consumer, derive the partition count, then compare N and 2N partitions for recovery time and files per hour.

What a rebalance repeats

Redeploy one consumer of a 12-member group on a 24-partition topic, many times: count what eager, cooperative and static membership process twice.

The length-prefix attack and the maximum frame size

A server that trusts a 4-byte length header, a header claiming 4 GB, and one wrong length in the middle of a stream.

Batch size is a compression parameter

Compress 100,000 small JSON events in batches of 1 to 10,000, then with a trained dictionary.

Compress or not: the rate comparison

compress + transfer + decompress against sending raw, for five codecs and three link speeds.

Stale pooled connections: find out what your pool does

Exhaust a pool of 2, kill a proxy silently under a pooled connection, and read your HTTP library's defaults.

Nagle plus delayed ACK: reproduce the 40 ms cliff

Two small writes and a short reply: Nagle on the sender and delayed ACK on the receiver add about 40 ms per call.

Dedup window versus replay

A 60-second dedup window against a replay five minutes later, then idempotency by replacing the partition.

Reconciliation count and duplicate-rate metric

Count records per hour at source and sink, then plant a bug that swallows 1% of writes: errors stay at zero, the count gap does not.