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articles/cosmos-db/consistency-levels.md

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# Consistency levels in Azure Cosmos DB
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[!INCLUDE[appliesto-all-apis](includes/appliesto-all-apis.md)]
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Distributed databases that rely on replication for high availability, low latency, or both, must make a fundamental tradeoff between the read consistency, availability, latency, and throughput as defined by the [PACELC theorem](https://en.wikipedia.org/wiki/PACELC_theorem). The linearizability of the strong consistency model is the gold standard of data programmability. But it adds a steep price from higher write latencies due to data having to replicate and commit across large distances. Strong consistency may also suffer from reduced availability (during failures) because data cannot replicate and commit in every region. Eventual consistency offers higher availability and better performance, but its more difficult to program applications because data may not be completely consistent across all regions.
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Distributed databases that rely on replication for high availability, low latency, or both, must make a fundamental tradeoff between the read consistency, availability, latency, and throughput as defined by the [PACELC theorem](https://en.wikipedia.org/wiki/PACELC_theorem). The linearizability of the strong consistency model is the gold standard of data programmability. But it adds a steep price from higher write latencies due to data having to replicate and commit across large distances. Strong consistency may also suffer from reduced availability (during failures) because data cannot replicate and commit in every region. Eventual consistency offers higher availability and better performance, but it's more difficult to program applications because data may not be completely consistent across all regions.
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Most commercially available distributed NoSQL databases available in the market today provide only strong and eventual consistency. Azure Cosmos DB offers five well-defined levels. From strongest to weakest, the levels are:
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You can configure the default consistency level on your Azure Cosmos account at any time. The default consistency level configured on your account applies to all Azure Cosmos databases and containers under that account. All reads and queries issued against a container or a database use the specified consistency level by default. To learn more, see how to [configure the default consistency level](how-to-manage-consistency.md#configure-the-default-consistency-level). You can also override the default consistency level for a specific request, to learn more, see how to [Override the default consistency level](how-to-manage-consistency.md?#override-the-default-consistency-level) article.
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> [!TIP]
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> Overriding the default consistency level only applies to reads within the SDK client. An account configured for strong consistency by default will still write and replicate data synchronously to every region in the account. When the SDK client instance or request overrides this with Session or weaker consistency, reads will be performed using a single replica. See [Consistency levels and throughput](consistency-levels.md#consistency-levels-and-throughput) for more details.
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> Overriding the default consistency level only applies to reads within the SDK client. An account configured for strong consistency by default will still write and replicate data synchronously to every region in the account. When the SDK client instance or request overrides this with Session or weaker consistency, reads will be performed using a single replica. For more information, see [Consistency levels and throughput](consistency-levels.md#consistency-levels-and-throughput).
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> [!IMPORTANT]
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> It is required to recreate any SDK instance after changing the default consistency level. This can be done by restarting the application. This ensures the SDK uses the new default consistency level.

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