DD
WhatsApp · Deep Dives
Deep Dives
Eight deep dives — database, message ordering, offline delivery, message status, inbox, caching, peak traffic, and fault isolation.
Database
DB choice, schema, tiered storage, sharding, and hot partition detection and salting.
DynamoDBShardingHot PartitionSalting
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Message Ordering
Client vs server timestamps, the time machine problem, and per-conversation sequence with Redis INCR.
Per-Conv. SeqRedis INCRClock Skew
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Offline Delivery
Detecting offline users, pending deliveries table, push notification flow, and reconnect sync.
Offline QueuePush NotificationPending Deliveries
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Message Status
Three ticks implementation, status table, delivered ack, read receipts, and privacy settings.
Read ReceiptsThree TicksPrivacyLast Seen
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Inbox
Inbox load flow, N+1 problem, denormalization, Redis sorted set for conversation list.
N+1 ProblemDenormalizationRedis Sorted Set
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Caching
Message history cache, profile cache, cache invalidation, cold start, and coalescing.
Message CacheProfile CacheCold StartInvalidation
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Peak Traffic
Thundering herd, connection storm, rate limiting, backpressure, and load shedding.
Thundering HerdBackpressureConnection StormLoad Shedding
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Fault Isolation
Connection server failure, DynamoDB failure, Redis failure — each isolated with circuit breakers.
Reconnect StormCircuit BreakerRedis Failure
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