Cosmos db split transactional batches based on document size and other improvements #36964

JoasE · 2025-10-14T12:29:10Z

Cosmos db split transactional batches based on document size and other improvements

Improve performance for non-batching scenario's
Don't use batch for single entry updates
Fixes: #36903

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…r improvements Improve performance for non-batching scenario's Don't use batch for single entry updates Fixes: dotnet#36903

JoasE · 2025-10-14T14:08:31Z

src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs

+            // With AutoTransactionBehavior.Always, AddToTransaction will always return true.
+            if (!AddToTransaction(transaction, updateEntry, stream))
+            {
+                yield return transaction;


I've currently opted for always sending the transaction with AutoTransactionBehavior.Always, even if we think it is too big. Cosmos db will refuse the request and a DbUpdateException will be thrown. We could also opt for throwing an InvalidOperationException with the SaveChangesAutoTransactionBehaviorAlwaysAtomicity message (with a small change explaining 2MB) if we think the transaction won't be accepted due to it's size. We would need to add an if here to throw that exception

Suggested change

yield return transaction;

if (_currentDbContext.Context.Database.AutoTransactionBehavior == AutoTransactionBehavior.Always)

throw new InvalidOperationException();

yield return transaction;

src/EFCore.Cosmos/Storage/Internal/CosmosTransactionalBatchWrapper.cs

…et#36903

src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs

Copilot

Pull Request Overview

This PR enhances Cosmos DB transactional batch handling by implementing size-based batch splitting and performance optimizations. The changes address issue #36903 by introducing logic to split batches when they exceed the Cosmos DB 2 MiB request size limit and optimizing non-batching scenarios.

Key Changes:

Implements automatic batch splitting based on document size to stay within Cosmos DB's 2 MiB request limit
Optimizes single-entry updates by bypassing batch operations when AutoTransactionBehavior is not set to Always
Refactors serialization logic to avoid duplication and improve performance

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
`test/EFCore.Specification.Tests/BulkUpdates/NorthwindBulkUpdatesTestBase.cs`	Corrected assertion to use `Assert.Null` instead of `Assert.Equal(null, ...)`
`test/EFCore.Cosmos.FunctionalTests/EndToEndCosmosTest.cs`	Fixed inverted logic for transactional batch configuration
`test/EFCore.Cosmos.FunctionalTests/CosmosTransactionalBatchTest.cs`	Added comprehensive tests for batch splitting, size limits, and single-entry optimization
`src/EFCore.Cosmos/Storage/Internal/ICosmosTransactionalBatchWrapper.cs`	Updated interface to return boolean indicating success and accept streams instead of JToken
`src/EFCore.Cosmos/Storage/Internal/ICosmosClientWrapper.cs`	Updated interface methods to support size checking and renamed batch execution methods for clarity
`src/EFCore.Cosmos/Storage/Internal/CosmosTransactionalBatchWrapper.cs`	Implemented size tracking and batch splitting logic with 2 MiB limit enforcement
`src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs`	Refactored save logic to handle single-entry optimization and multiple transactions per batch
`src/EFCore.Cosmos/Storage/Internal/CosmosClientWrapper.cs`	Extracted serialization logic to a shared static method and updated method names

src/EFCore.Cosmos/Storage/Internal/CosmosTransactionalBatchWrapper.cs

src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs

src/EFCore.Cosmos/Storage/Internal/CosmosTransactionalBatchWrapper.cs

Co-authored-by: Andriy Svyryd <[email protected]>

…to fix/dotnet#36903

AndriySvyryd · 2025-10-23T23:21:50Z

Thanks for your contribution!

AndriySvyryd · 2025-10-24T16:07:19Z

test/EFCore.Cosmos.FunctionalTests/CosmosTransactionalBatchTest.cs

+    // The tests below will fail if the cosmos db sdk is updated and the serialization logic for transactional batches has changed
+
+    [ConditionalTheory, InlineData(true), InlineData(false)]
+    public virtual async Task SaveChanges_transaction_behaviour_always_single_entity_payload_can_be_exactly_cosmos_limit_and_throws_when_1byte_over(bool oneByteOver)


@JoasE On a real Cosmos account this test fails consistently for oneByteOver: true, no exceptions are thrown

:( That probably means the request body limit for a real cosmos db and the emulator are different

@AndriySvyryd In that case I think it's going to be tough to add tests to validate whether internal cosmos sdk serialization logic has changed. We might be ok without that kind of tests tho. Then we only validate whether we don't get an exception if we are at our perceived limit

I can create a pr that changes the tests if you want?

:( That means the request body limit for a real cosmos db and the emulator are different

It failing for true means the limit is higher on a real cosmos db tho

Perhaps we can change this one to be +1024 instead of +1 to give us some wiggle room (even if it defeats the main purpose for this test)

@AndriySvyryd Are you sure the test will succeed on a real cosmos db with that extra?

@AndriySvyryd We could also consider this: #37028

It does, though I haven't yet determined the exact value.
Alternatively, we could set the actual limit to what the real Cosmos uses and mark this test with
[CosmosCondition(CosmosCondition.IsNotEmulator)]

Looks like the minimum value for real Cosmos is +7

JoasE added 2 commits October 14, 2025 14:27

Cosmos db split transactional batches based on document size and othe…

965aa3f

…r improvements Improve performance for non-batching scenario's Don't use batch for single entry updates Fixes: dotnet#36903

Cleanup

0145c82

JoasE commented Oct 14, 2025

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src/EFCore.Cosmos/Storage/Internal/CosmosTransactionalBatchWrapper.cs Outdated Show resolved Hide resolved

JoasE mentioned this pull request Oct 14, 2025

Cosmos 11.0 CUD batching RequestEntityTooLarge errors #36903

Closed

JoasE marked this pull request as ready for review October 14, 2025 14:16

JoasE requested a review from a team as a code owner October 14, 2025 14:16

cincuranet assigned roji Oct 15, 2025

roji assigned AndriySvyryd Oct 17, 2025

JoasE added 2 commits October 18, 2025 19:06

Merge branch 'main' of https://github.com/dotnet/efcore into fix/dotn…

86057af

…et#36903

Merge branch 'main' of https://github.com/dotnet/efcore into fix/dotn…

8834d84

…et#36903

AndriySvyryd reviewed Oct 23, 2025

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AndriySvyryd requested a review from Copilot October 23, 2025 00:34

Copilot AI reviewed Oct 23, 2025

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src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs Outdated Show resolved Hide resolved

AndriySvyryd reviewed Oct 23, 2025

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AndriySvyryd reviewed Oct 23, 2025

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AndriySvyryd added the community-contribution label Oct 23, 2025

JoasE and others added 5 commits October 23, 2025 11:42

Update src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs

45e5906

Co-authored-by: Andriy Svyryd <[email protected]>

Use _size instead of _entries.Count for checking if batch is empty

4304c5b

Use .Length for IfMatchEtag size

50aab89

Add tests to validate id duplicate on update but not on create

6a8c2f2

Merge branch 'fix/dotnet#36903' of https://github.com/JoasE/efcore in…

611dab1

…to fix/dotnet#36903

AndriySvyryd approved these changes Oct 23, 2025

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AndriySvyryd merged commit 52d11df into dotnet:main Oct 23, 2025
7 checks passed

dotnet-maestro bot mentioned this pull request Oct 24, 2025

[main] Source code updates from dotnet/efcore dotnet/dotnet#3086

Merged

AndriySvyryd reviewed Oct 24, 2025

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Cosmos db split transactional batches based on document size and other improvements #36964

Cosmos db split transactional batches based on document size and other improvements #36964

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JoasE commented Oct 14, 2025

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AndriySvyryd commented Oct 23, 2025

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JoasE Oct 24, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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JoasE Oct 24, 2025 •

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