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Fixed concurrency issue in MetaDb chunk expansion #9508

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Merged
michaelstaib merged 2 commits into from
Apr 7, 2026
Merged

Fixed concurrency issue in MetaDb chunk expansion #9508

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60a1945
Fixed concurrency issue in MetaDb chunk expansion
michaelstaib Apr 7, 2026
cfdf02e
Merge branch 'main' into mst/metadb-expansion
michaelstaib Apr 7, 2026
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43 changes: 36 additions & 7 deletions src/HotChocolate/Core/src/Types/Text/Json/ResultDocument.MetaDb.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,9 @@ internal struct MetaDb : IDisposable
private static readonly ArrayPool<byte[]> s_arrayPool = ArrayPool<byte[]>.Shared;

private byte[][] _chunks;
private byte[][]? _previousChunks;
private Cursor _next;
private volatile uint _nextValue;
private bool _disposed;

internal static MetaDb CreateForEstimatedRows(int estimatedRows)
Expand All @@ -38,11 +40,20 @@ internal static MetaDb CreateForEstimatedRows(int estimatedRows)
return new MetaDb
{
_chunks = chunks,
_next = Cursor.Zero
_next = Cursor.Zero,
_nextValue = Cursor.Zero.Value
};
}

public Cursor NextCursor => _next;
public readonly Cursor NextCursor
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
var value = _nextValue;
return Unsafe.As<uint, Cursor>(ref value);
}
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Cursor Append(
Expand Down Expand Up @@ -87,9 +98,16 @@ internal Cursor Append(
newChunks[i] = [];
}

// clear and return old chunks buffer
chunks.Clear();
s_arrayPool.Return(_chunks);
// Concurrent readers may still reference the current chunks array.
// Return the previously retained one and keep the current one
// alive until the next expansion or Dispose.
if (_previousChunks is not null)
{
_previousChunks.AsSpan().Clear();
s_arrayPool.Return(_previousChunks);
}

_previousChunks = _chunks;

// assign new chunks buffer
_chunks = newChunks;
Expand Down Expand Up @@ -119,7 +137,9 @@ internal Cursor Append(
Unsafe.WriteUnaligned(ref Unsafe.Add(ref dest, byteOffset), row);

// Advance write head by one row
_next = next + 1;
var newNext = next + 1;
_next = newNext;
_nextValue = newNext.Value;
return next;
}

Expand Down Expand Up @@ -331,7 +351,9 @@ private void AssertValidCursor(Cursor cursor)
Debug.Assert(cursor.Chunk < _chunks.Length, "Chunk index out of bounds");
Debug.Assert(_chunks[cursor.Chunk].Length > 0, "Accessing unallocated chunk");

var maxExclusive = _next.Chunk * Cursor.RowsPerChunk + _next.Row;
var value = _nextValue;
var maxCursor = Unsafe.As<uint, Cursor>(ref value);
var maxExclusive = maxCursor.Chunk * Cursor.RowsPerChunk + maxCursor.Row;
var absoluteIndex = (cursor.Chunk * Cursor.RowsPerChunk) + cursor.Row;

Debug.Assert(absoluteIndex >= 0 && absoluteIndex < maxExclusive,
Expand All @@ -348,6 +370,13 @@ public void Dispose()
var chunks = _chunks.AsSpan(0, chunksLength);
Log.MetaDbDisposed(2, chunksLength, cursor.Row);

if (_previousChunks is not null)
{
_previousChunks.AsSpan().Clear();
s_arrayPool.Return(_previousChunks);
_previousChunks = null;
}

foreach (var chunk in chunks)
{
if (chunk.Length == 0)
Expand Down
134 changes: 134 additions & 0 deletions src/HotChocolate/Core/test/Execution.Tests/Integration/DataLoader/Issue9500Tests.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,134 @@
using GreenDonut;
using HotChocolate.Types;
using Microsoft.Extensions.DependencyInjection;
using static HotChocolate.Tests.TestHelper;

namespace HotChocolate.Execution.Integration.DataLoader;

public class Issue9500Tests
{
[Fact]
public async Task Composite_DataLoader_Result_Overflows_Selection_Buffer_When_Paging_Many_Nodes()
{
const int nodeCount = 100_000;

var executor = await CreateExecutorAsync(
c => c
.AddQueryType<Issue9500Query>()
.AddDataLoader<INoteDataLoader, NoteDataLoader>()
.ModifyRequestOptions(o => o.IncludeExceptionDetails = true));
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var result = await executor.ExecuteAsync(
OperationRequestBuilder.New()
.SetDocument(
$$"""
{
items(first: {{nodeCount}}) {
edges {
cursor
node {
id
note {
comment
dueDate
progress
assignee
status
priority
category
createdBy
updatedBy
title
summary
kind
owner
reviewer
milestone
}
}
}
}
}
""")
.Build());

Assert.Empty(result.ExpectOperationResult().Errors);
}

public class Issue9500Query
{
[UsePaging(DefaultPageSize = 100000, MaxPageSize = 100000)]
public IEnumerable<Item> GetItems()
=> Enumerable.Range(0, 100_000).Select(i => new Item(i));
}
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public class Item(int id)
{
public int Id { get; } = id;

public Task<Note?> GetNoteAsync(
INoteDataLoader dataLoader,
CancellationToken cancellationToken)
=> dataLoader.LoadAsync(Id, cancellationToken);
}

public interface INoteDataLoader
: IDataLoader<int, Note>;

public class NoteDataLoader(
IBatchScheduler batchScheduler,
DataLoaderOptions options)
: BatchDataLoader<int, Note>(batchScheduler, options), INoteDataLoader
{
protected override Task<IReadOnlyDictionary<int, Note>> LoadBatchAsync(
IReadOnlyList<int> keys,
CancellationToken cancellationToken)
{
return LoadAsync(keys, cancellationToken);
}

private static async Task<IReadOnlyDictionary<int, Note>> LoadAsync(
IReadOnlyList<int> keys,
CancellationToken cancellationToken)
{
await Task.Delay(1, cancellationToken);
cancellationToken.ThrowIfCancellationRequested();

return keys.ToDictionary(
key => key,
key => new Note(
$"Comment {key}",
$"2026-04-{(key % 28) + 1:00}",
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key % 100,
$"Assignee {key}",
key % 2 == 0 ? "Open" : "Closed",
$"P{key % 5}",
$"Category {key % 7}",
$"Creator {key % 11}",
$"Updater {key % 13}",
$"Title {key}",
$"Summary {key}",
$"Kind {key % 3}",
$"Owner {key % 17}",
$"Reviewer {key % 19}",
$"Milestone {key % 23}"));
}
}

public record Note(
string Comment,
string DueDate,
int Progress,
string Assignee,
string Status,
string Priority,
string Category,
string CreatedBy,
string UpdatedBy,
string Title,
string Summary,
string Kind,
string Owner,
string Reviewer,
string Milestone);
}
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