Is the Cosmos DB documentation example on session consistency misleading?

Question

Is the Cosmos DB documentation example on session consistency misleading?

AZOK 0

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

The Cosmos DB documentation example on session consistency states:

Whereas the "Australia East" region is using "Session B" so, it receives data later but in the same order as the writes.

In the example there is a single writer writing in session A, and a reader reading in session B in another region. The quote implies that there is some sort of ordering guarantee for the session B reader? I would have assumed to see eventual consistency for the session B reader, i.e. the writes may end up being read in an incorrect order. Which is correct?

Continuing with the same example, does the session consistency level include the consistent prefix guarantee? Is the session B reader guaranteed to see consistent prefix reads? I believe one can explicitly set a read request to use a lower consistency level, so I should be able to get consistent prefix guarantees outside of a session at least by explicitly requesting it, if it isn't included by default?

AZOK 0 Reputation points

2025-08-03T13:36:05.37+00:00

Thank you for the answer.

So the consistent prefix guarantee is not included in the session consistency level (outside of the session), but I could explicitly request a consistent prefix guarantee for my read requests using the SDK? For example, I could request consistent prefix consistency level for every single one of the reads the session B reader made? => I would get consistent prefix reads even though I am not in the session where the writes are being made. Is this correct?
Mahesh Kurva 6,850 Reputation points Microsoft External Staff Moderator

2025-08-04T06:53:37.8166667+00:00

Hi AZOK ,

Yes, as documented by Microsoft, you can override the default consistency level per request using the SDK. If your reader in Session B uses ConsistentPrefix, it will get reads that preserve the order of writes, even if it's not the writer’s session. However, it will not get read-your-writes or monotonic reads.

See Azure Cosmos DB consistency levels for official reference.

I hope this information helps. Please do let us know if you have any further queries.
Mahesh Kurva 6,850 Reputation points Microsoft External Staff Moderator

2025-08-05T02:37:21.37+00:00

Hi AZOK ,

Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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AZOK 0 Reputation points

2025-08-03T13:36:05.37+00:00

Thank you for the answer.

So the consistent prefix guarantee is not included in the session consistency level (outside of the session), but I could explicitly request a consistent prefix guarantee for my read requests using the SDK? For example, I could request consistent prefix consistency level for every single one of the reads the session B reader made? => I would get consistent prefix reads even though I am not in the session where the writes are being made. Is this correct?
Mahesh Kurva 6,850 Reputation points Microsoft External Staff Moderator

2025-08-04T06:53:37.8166667+00:00

Hi AZOK ,

Yes, as documented by Microsoft, you can override the default consistency level per request using the SDK. If your reader in Session B uses ConsistentPrefix, it will get reads that preserve the order of writes, even if it's not the writer’s session. However, it will not get read-your-writes or monotonic reads.

See Azure Cosmos DB consistency levels for official reference.

I hope this information helps. Please do let us know if you have any further queries.
Mahesh Kurva 6,850 Reputation points Microsoft External Staff Moderator

2025-08-05T02:37:21.37+00:00

Hi AZOK ,

Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 1

Hi AZOK ,

GreetingS!!

It sounds like you’re trying to clarify a couple of points regarding the session consistency example in Azure Cosmos DB documentation.

What Session Consistency Guarantees

Session consistency ensures the following for a single client session:

Read-your-writes: A client will always see its own writes.
Monotonic reads: Once a client reads a value, it will not see an older value in subsequent reads.
Monotonic writes: Writes are serialized in the order they were issued by the client.
Writes-follow-reads: A write operation following a read is guaranteed to be based on the latest read.

The Confusion in the Documentation

The documentation example says:

"Whereas the 'Australia East' region is using 'Session B' so, it receives data later but in the same order as the writes."

This can be misleading if interpreted as a cross-session guarantee. Here's why:

Session B is a different session from the writer's session (Session A).
Session consistency does not guarantee ordering across sessios.
Therefore, Session B may see writes out of order or not at all, unless it happens to read after the data has propagated and is available in the correct order.

So you're correct: Session B should not expect consistent prefix or ordered reads unless it is the same session as the writer.

Does Session Consistency Include Consistent Prefix?

No, session consistency does not include consistent prefix guarantees for other sessions. The consistent prefix level ensures that all clients see writes in the order they were committed, but it does not guarantee read-your-writes or monotonic reads.

Hope this helps. Do let us know if you any further queries.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Mahesh Kurva 6,850 Reputation points Microsoft External Staff Moderator

2025-08-06T05:58:28.3166667+00:00

Hi AZOK ,

Following up to see if the above answer was helpful. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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Is the Cosmos DB documentation example on session consistency misleading?

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