Work out stream shard count instantly with clear inputs, formula shown and shareable results.
A stream shard has three independent limits: 1 MB/s and 1,000 records per second for writes, and 2 MB/s for reads shared across all consumers. Multiple consumer applications each read the full stream, so read throughput often binds first — three consumers on a 35 MB/s stream need enough shards for 105 MB/s of reads.
Shard count
write shards = ceil(MB/s / 1); record shards = ceil(records / 1000); read shards = ceil(MB/s x consumers / 2); shards = max of the three
Enhanced fan-out gives each consumer its own dedicated 2 MB/s per shard, at extra cost per consumer-shard-hour. It also reduces propagation latency.
A partition key with low cardinality or heavy skew. Records with the same key always land on the same shard, so one popular key throttles that shard regardless of total capacity.