Cosmos DB 可能 window 的陈旧读取与 Session 在单个区域中的一致性

Question

According to the Microsoft docs: "single client session reads are guaranteed to honor the consistent-prefix, monotonic reads, monotonic writes, read-your-writes, and write-follows-reads guarantees"

As I understand, a separate client/session would observe Consistent Prefix reads.

1. Is this due to local replica sets which have yet to be updated?

2. Are there any guarantees on how long it take and what the possible window of a stale read is?

I'm trying to understand what the tradeoff is and whether the additional costs of Bounded Staleness consistency is worth it.

https://learn.microsoft.com/en-us/azure/cosmos-db/consistency-levels#session-consistency

Answer 1

Yes, it is because reads are from a single replica and may not see the latest update but will get all updates in order written. All data is written to 3 replicas.

There are no guarantees for how quickly data is replicated to the fourth replica. And while there is no guidance how quickly data is consistent across a replica set, the service will try to commit data into the fourth replica as quickly as possible.

It's only when using Bounded Staleness that the service will throttle writes if data is not fully replicated within 5 seconds or 10 updates.