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Fix to #35239 - EF9: SaveChanges() is significantly slower in .NET9 v…
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…s. .NET8 when using .ToJson() Mapping vs. PostgreSQL Legacy POCO mapping

Problem was that as part of AOT refactoring we changed way that we build comparers. Specifically, comparers of collections - ListOfValueTypesComparer, ListOfNullableValueTypesComparer and ListOfReferenceTypesComparer. Before those list comparer Compare, Hashcode and Snapshot methods would take as argument element comparer, which was responsible for comparing elements. We need to be able to express these in code for AOT but we are not able to generate constant of type ValueComparer (or ValueComparer) that was needed. As a solution, each comparer now stores expression describing how it can be constructed, so we use that instead (as we are perfectly capable to expressing that in code form). Problem is that now every time compare, snapshot or hashcode method is called for array type, we construct new ValueComparer for the element type. As a result in the reported case we would generate 1000s of comparers which all have to be compiled and that causes huge overhead.

Fix is to pass relevant func from the element comparer to the outer comparer. We only passed the element comparer object to the outer Compare/Hashcode/Snapshot function to call that relevant func. This way we avoid constructing redundant comparers.

For ListOfReferenceTypesComparer it's a bit trickier - TElement of the outer comparer doesn't always match TElement of the element comparer. If we detect this case, we see if the lambdas (Equals, Hashcode, Snapshot) are compatible between what we expect (in the list comparer method) and what we get from the element comparer. If they are compatible we just pass the element lambda to the list method. If they are not compatible we rewrite the element lambda so that they match.

Fixes #35239
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@maumar
maumar committed Dec 19, 2024
1 parent 321d5c6 commit c8d3f3f
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103 changes: 82 additions & 21 deletions src/EFCore.Cosmos/ChangeTracking/Internal/StringDictionaryComparer.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -15,13 +15,13 @@ namespace Microsoft.EntityFrameworkCore.Cosmos.ChangeTracking.Internal;
public sealed class StringDictionaryComparer<TDictionary, TElement> : ValueComparer<object>, IInfrastructure<ValueComparer>
{
private static readonly MethodInfo CompareMethod = typeof(StringDictionaryComparer<TDictionary, TElement>).GetMethod(
nameof(Compare), BindingFlags.Static | BindingFlags.NonPublic, [typeof(object), typeof(object), typeof(ValueComparer)])!;
nameof(Compare), BindingFlags.Static | BindingFlags.NonPublic, [typeof(object), typeof(object), typeof(Func<TElement, TElement, bool>)])!;

private static readonly MethodInfo GetHashCodeMethod = typeof(StringDictionaryComparer<TDictionary, TElement>).GetMethod(
nameof(GetHashCode), BindingFlags.Static | BindingFlags.NonPublic, [typeof(IEnumerable), typeof(ValueComparer)])!;
nameof(GetHashCode), BindingFlags.Static | BindingFlags.NonPublic, [typeof(IEnumerable), typeof(Func<TElement, int>)])!;

private static readonly MethodInfo SnapshotMethod = typeof(StringDictionaryComparer<TDictionary, TElement>).GetMethod(
nameof(Snapshot), BindingFlags.Static | BindingFlags.NonPublic, [typeof(object), typeof(ValueComparer)])!;
nameof(Snapshot), BindingFlags.Static | BindingFlags.NonPublic, [typeof(object), typeof(Func<TElement, TElement>)])!;

/// <summary>
/// This is an internal API that supports the Entity Framework Core infrastructure and not subject to
Expand Down Expand Up @@ -52,14 +52,40 @@ ValueComparer IInfrastructure<ValueComparer>.Instance
var prm1 = Expression.Parameter(typeof(object), "a");
var prm2 = Expression.Parameter(typeof(object), "b");

// we check the compatibility of expected equals lambda signature Func<TElement, TElement, bool>
// vs method we actually get from the element comparer, which would be typed to its generic argument
// if the expected is assignable from actual we can just do simple call...
var expectedSignature = typeof(Func<TElement, TElement, bool>);
var actualSignature = typeof(Func<,,>).MakeGenericType(elementComparer.Type, elementComparer.Type, typeof(bool));
if (expectedSignature.IsAssignableFrom(actualSignature))
{
return Expression.Lambda<Func<object?, object?, bool>>(
Expression.Call(
CompareMethod,
prm1,
prm2,
elementComparer.EqualsExpression),
prm1,
prm2);
}

// ...otherwise we need to rewrite the actual lambda (as we can't change the expected signature)
// in that case we are rewriting the inner lambda parameters to TElement and cast to the element comparer
// type argument in the body, so that semantics of the element comparison func don't change
var newInnerPrm1 = Expression.Parameter(typeof(TElement), "a");
var newInnerPrm2 = Expression.Parameter(typeof(TElement), "b");

return Expression.Lambda<Func<object?, object?, bool>>(
Expression.Call(
CompareMethod,
prm1,
prm2,
#pragma warning disable EF9100
elementComparer.ConstructorExpression),
#pragma warning restore EF9100
Expression.Lambda(
elementComparer.ExtractEqualsBody(
Expression.Convert(newInnerPrm1, elementComparer.Type),
Expression.Convert(newInnerPrm2, elementComparer.Type)),
newInnerPrm1,
newInnerPrm2)),
prm1,
prm2);
}
Expand All @@ -68,33 +94,68 @@ private static Expression<Func<object, int>> GetHashCodeLambda(ValueComparer ele
{
var prm = Expression.Parameter(typeof(object), "o");

var expectedSignature = typeof(Func<TElement, int>);
var actualSignature = typeof(Func<,>).MakeGenericType(elementComparer.Type, typeof(int));
if (expectedSignature.IsAssignableFrom(actualSignature))
{
return Expression.Lambda<Func<object, int>>(
Expression.Call(
GetHashCodeMethod,
Expression.Convert(
prm,
typeof(IEnumerable)),
elementComparer.HashCodeExpression),
prm);
}

var newInnerPrm = Expression.Parameter(typeof(TElement), "o");

return Expression.Lambda<Func<object, int>>(
Expression.Call(
GetHashCodeMethod,
Expression.Convert(
prm,
typeof(IEnumerable)),
#pragma warning disable EF9100
elementComparer.ConstructorExpression),
#pragma warning restore EF9100
Expression.Lambda(
elementComparer.ExtractHashCodeBody(
Expression.Convert(newInnerPrm, elementComparer.Type)),
newInnerPrm)),
prm);
}

private static Expression<Func<object, object>> SnapshotLambda(ValueComparer elementComparer)
{
var prm = Expression.Parameter(typeof(object), "source");

var expectedSignature = typeof(Func<TElement, TElement>);
var actualSignature = typeof(Func<,>).MakeGenericType(elementComparer.Type, elementComparer.Type);
if (expectedSignature.IsAssignableFrom(actualSignature))
{
return Expression.Lambda<Func<object, object>>(
Expression.Call(
SnapshotMethod,
prm,
elementComparer.SnapshotExpression),
prm);
}

var newInnerPrm = Expression.Parameter(typeof(TElement), "source");

// note we need to also convert the result of inner lambda back to TElement
return Expression.Lambda<Func<object, object>>(
Expression.Call(
SnapshotMethod,
prm,
#pragma warning disable EF9100
elementComparer.ConstructorExpression),
#pragma warning restore EF9100
Expression.Lambda(
Expression.Convert(
elementComparer.ExtractSnapshotBody(
Expression.Convert(newInnerPrm, elementComparer.Type)),
typeof(TElement)),
newInnerPrm)),
prm);
}

private static bool Compare(object? a, object? b, ValueComparer elementComparer)
private static bool Compare(object? a, object? b, Func<TElement?, TElement?, bool> elementCompare)
{
if (ReferenceEquals(a, b))
{
Expand All @@ -121,7 +182,7 @@ private static bool Compare(object? a, object? b, ValueComparer elementComparer)
foreach (var pair in aDictionary)
{
if (!bDictionary.TryGetValue(pair.Key, out var bValue)
|| !elementComparer.Equals(pair.Value, bValue))
|| !elementCompare(pair.Value, bValue))
{
return false;
}
Expand All @@ -133,44 +194,44 @@ private static bool Compare(object? a, object? b, ValueComparer elementComparer)
throw new InvalidOperationException(
CosmosStrings.BadDictionaryType(
(a is IDictionary<string, TElement?> ? b : a).GetType().ShortDisplayName(),
typeof(IDictionary<,>).MakeGenericType(typeof(string), elementComparer.Type).ShortDisplayName()));
typeof(IDictionary<,>).MakeGenericType(typeof(string), typeof(TElement)).ShortDisplayName()));
}

private static int GetHashCode(IEnumerable source, ValueComparer elementComparer)
private static int GetHashCode(IEnumerable source, Func<TElement?, int> elementGetHashCode)
{
if (source is not IReadOnlyDictionary<string, TElement?> sourceDictionary)
{
throw new InvalidOperationException(
CosmosStrings.BadDictionaryType(
source.GetType().ShortDisplayName(),
typeof(IList<>).MakeGenericType(elementComparer.Type).ShortDisplayName()));
typeof(IList<>).MakeGenericType(typeof(TElement)).ShortDisplayName()));
}

var hash = new HashCode();

foreach (var pair in sourceDictionary)
{
hash.Add(pair.Key);
hash.Add(pair.Value == null ? 0 : elementComparer.GetHashCode(pair.Value));
hash.Add(pair.Value == null ? 0 : elementGetHashCode(pair.Value));
}

return hash.ToHashCode();
}

private static IReadOnlyDictionary<string, TElement?> Snapshot(object source, ValueComparer elementComparer)
private static IReadOnlyDictionary<string, TElement?> Snapshot(object source, Func<TElement?, TElement?> elementSnapshot)
{
if (source is not IReadOnlyDictionary<string, TElement?> sourceDictionary)
{
throw new InvalidOperationException(
CosmosStrings.BadDictionaryType(
source.GetType().ShortDisplayName(),
typeof(IDictionary<,>).MakeGenericType(typeof(string), elementComparer.Type).ShortDisplayName()));
typeof(IDictionary<,>).MakeGenericType(typeof(string), typeof(TElement)).ShortDisplayName()));
}

var snapshot = new Dictionary<string, TElement?>();
foreach (var pair in sourceDictionary)
{
snapshot[pair.Key] = pair.Value == null ? default : (TElement?)elementComparer.Snapshot(pair.Value);
snapshot[pair.Key] = pair.Value == null ? default : (TElement?)elementSnapshot(pair.Value);
}

return snapshot;
Expand Down
42 changes: 18 additions & 24 deletions src/EFCore/ChangeTracking/ListOfNullableValueTypesComparer.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -33,15 +33,15 @@ public sealed class ListOfNullableValueTypesComparer<TConcreteList, TElement> :

private static readonly MethodInfo CompareMethod = typeof(ListOfNullableValueTypesComparer<TConcreteList, TElement>).GetMethod(
nameof(Compare), BindingFlags.Static | BindingFlags.NonPublic,
[typeof(IEnumerable<TElement?>), typeof(IEnumerable<TElement?>), typeof(ValueComparer<TElement?>)])!;
[typeof(IEnumerable<TElement?>), typeof(IEnumerable<TElement?>), typeof(Func<TElement?, TElement?, bool>)])!;

private static readonly MethodInfo GetHashCodeMethod = typeof(ListOfNullableValueTypesComparer<TConcreteList, TElement>).GetMethod(
nameof(GetHashCode), BindingFlags.Static | BindingFlags.NonPublic,
[typeof(IEnumerable<TElement?>), typeof(ValueComparer<TElement?>)])!;
[typeof(IEnumerable<TElement?>), typeof(Func<TElement?, int>)])!;

private static readonly MethodInfo SnapshotMethod = typeof(ListOfNullableValueTypesComparer<TConcreteList, TElement>).GetMethod(
nameof(Snapshot), BindingFlags.Static | BindingFlags.NonPublic,
[typeof(IEnumerable<TElement?>), typeof(ValueComparer<TElement?>)])!;
[typeof(IEnumerable<TElement?>), typeof(Func<TElement?, TElement?>)])!;

/// <summary>
/// Creates a new instance of the list comparer.
Expand All @@ -67,15 +67,13 @@ ValueComparer IInfrastructure<ValueComparer>.Instance
var prm1 = Expression.Parameter(typeof(IEnumerable<TElement?>), "a");
var prm2 = Expression.Parameter(typeof(IEnumerable<TElement?>), "b");

//(a, b) => Compare(a, b, (ValueComparer<TElement?>)elementComparer)
//(a, b) => Compare(a, b, elementComparer.Equals)
return Expression.Lambda<Func<IEnumerable<TElement?>?, IEnumerable<TElement?>?, bool>>(
Expression.Call(
CompareMethod,
prm1,
prm2,
Expression.Convert(
elementComparer.ConstructorExpression,
typeof(ValueComparer<TElement?>))),
elementComparer.EqualsExpression),
prm1,
prm2);
}
Expand All @@ -84,33 +82,29 @@ ValueComparer IInfrastructure<ValueComparer>.Instance
{
var prm = Expression.Parameter(typeof(IEnumerable<TElement?>), "o");

//o => GetHashCode(o, (ValueComparer<TElement?>)elementComparer)
//o => GetHashCode(o, elementComparer.GetHashCode)
return Expression.Lambda<Func<IEnumerable<TElement?>, int>>(
Expression.Call(
GetHashCodeMethod,
prm,
Expression.Convert(
elementComparer.ConstructorExpression,
typeof(ValueComparer<TElement?>))),
elementComparer.HashCodeExpression),
prm);
}

private static Expression<Func<IEnumerable<TElement?>, IEnumerable<TElement?>>> SnapshotLambda(ValueComparer elementComparer)
{
var prm = Expression.Parameter(typeof(IEnumerable<TElement?>), "source");

//source => Snapshot(source, (ValueComparer<TElement?>)elementComparer)
//source => Snapshot(source, elementComparer.Snapshot)
return Expression.Lambda<Func<IEnumerable<TElement?>, IEnumerable<TElement?>>>(
Expression.Call(
SnapshotMethod,
prm,
Expression.Convert(
elementComparer.ConstructorExpression,
typeof(ValueComparer<TElement?>))),
elementComparer.SnapshotExpression),
prm);
}

private static bool Compare(IEnumerable<TElement?>? a, IEnumerable<TElement?>? b, ValueComparer<TElement?> elementComparer)
private static bool Compare(IEnumerable<TElement?>? a, IEnumerable<TElement?>? b, Func<TElement?, TElement?, bool> elementCompare)
{
if (ReferenceEquals(a, b))
{
Expand Down Expand Up @@ -152,7 +146,7 @@ private static bool Compare(IEnumerable<TElement?>? a, IEnumerable<TElement?>? b
return false;
}

if (!elementComparer.Equals(el1, el2))
if (!elementCompare(el1, el2))
{
return false;
}
Expand All @@ -164,29 +158,29 @@ private static bool Compare(IEnumerable<TElement?>? a, IEnumerable<TElement?>? b
throw new InvalidOperationException(
CoreStrings.BadListType(
(a is IList<TElement?> ? b : a).GetType().ShortDisplayName(),
typeof(IList<>).MakeGenericType(elementComparer.Type.MakeNullable()).ShortDisplayName()));
typeof(IList<>).MakeGenericType(typeof(TElement).MakeNullable()).ShortDisplayName()));
}

private static int GetHashCode(IEnumerable<TElement?> source, ValueComparer<TElement?> elementComparer)
private static int GetHashCode(IEnumerable<TElement?> source, Func<TElement?, int> elementGetHashCode)
{
var hash = new HashCode();

foreach (var el in source)
{
hash.Add(el == null ? 0 : elementComparer.GetHashCode(el));
hash.Add(el == null ? 0 : elementGetHashCode(el));
}

return hash.ToHashCode();
}

private static IList<TElement?> Snapshot(IEnumerable<TElement?> source, ValueComparer<TElement?> elementComparer)
private static IList<TElement?> Snapshot(IEnumerable<TElement?> source, Func<TElement?, TElement?> elementSnapshot)
{
if (source is not IList<TElement?> sourceList)
{
throw new InvalidOperationException(
CoreStrings.BadListType(
source.GetType().ShortDisplayName(),
typeof(IList<>).MakeGenericType(elementComparer.Type.MakeNullable()).ShortDisplayName()));
typeof(IList<>).MakeGenericType(typeof(TElement).MakeNullable()).ShortDisplayName()));
}

if (IsArray)
Expand All @@ -195,7 +189,7 @@ private static int GetHashCode(IEnumerable<TElement?> source, ValueComparer<TEle
for (var i = 0; i < sourceList.Count; i++)
{
var instance = sourceList[i];
snapshot[i] = instance == null ? null : elementComparer.Snapshot(instance);
snapshot[i] = instance == null ? null : elementSnapshot(instance);
}

return snapshot;
Expand All @@ -205,7 +199,7 @@ private static int GetHashCode(IEnumerable<TElement?> source, ValueComparer<TEle
var snapshot = IsReadOnly ? new List<TElement?>() : (IList<TElement?>)Activator.CreateInstance<TConcreteList>()!;
foreach (var e in sourceList)
{
snapshot.Add(e == null ? null : elementComparer.Snapshot(e));
snapshot.Add(e == null ? null : elementSnapshot(e));
}

return IsReadOnly
Expand Down
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