Isolation guaranteesIn order to prioritize extreme availability, the system throws traditional isolation guarantees out the window. The paper says ANSI SQL-style isolation and strict consistency cannot survive at scale in this architecture. The atomicity protocol prevents dirty reads by ensuring only fully committed logs leave a client’s private queue, but commit-time read-write and write-write conflicts are ignored entirely! If two clients hit the same record, the last-writer wins. So lost updates are common. To make this usable, the authors push consistency up to the client. For ensuring monotonic reads, each client tracks the highest commit timestamp it has seen, and if it sees any older version from S3 it rejects it and rereads. For monotonic writes, the client stamps version counters on log records and page headers. Checkpoints sort logs and defer any out-of-order SQS messages so each client’s writes stay in order.
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