Consistency Levels
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Category: Data Distribution & Consistency
Summary: Five tunable levels (Strong, Bounded Staleness, Session, Consistent Prefix, Eventual).
Overview
Azure Cosmos DB offers five well-defined, tunable consistency levels, trading off between consistency, availability, latency, and RU cost: Strong (linearizable reads, highest consistency, lowest availability/highest latency), Bounded Staleness (reads lag writes by a bounded time/version window), Session (default; strong consistency within a single client session), Consistent Prefix (reads never see out-of-order writes), and Eventual (lowest consistency, highest availability and lowest latency). The default consistency level is configured at the account level.When an application makes a read request, it can override this default consistency level dynamically per request, but only to a weaker or equal consistency level.
ReadConsistencyStrategy is an exception that allows stronger read consistency than the account default.
More Info & Links
DP-420 Style Practice Questions
Q1. What is the default consistency level in Azure Cosmos DB?
- A. Session
- B. Strong
- C. Eventual
- D. Consistent Prefix
Q2. Which consistency level offers the strongest guarantees but typically the highest latency and lowest availability during network partitions?
- A. Strong
- B. Eventual
- C. Consistent Prefix
- D. Session
Q3. Can the consistency level be overridden for an individual read request?
- A. Yes, you can relax (but not strengthen) the consistency level per request
- B. No, consistency is fixed permanently at account creation
- C. Yes, but only for write requests
- D. No, only Azure support can change it
Answer Key
Answers are listed at the very end so you can attempt the questions first.
- Q1 (Consistency Levels): A. Session — Session consistency is the default consistency level for new Azure Cosmos DB accounts.
- Q2 (Consistency Levels): A. Strong — Strong consistency provides linearizable reads, the highest consistency guarantee, at the cost of higher latency and lower availability.
- Q3 (Consistency Levels): A. Yes, you can relax (but not strengthen) the consistency level per request — You can override the default account consistency level to a weaker level on a per-request basis using query request options.
DP-420: Designing and Implementing Cloud-Native Applications Using Microsoft Azure Cosmos DB — term detail page
