Stop wrapping single changes in transactions where possible

src/EFCore.Relational/Migrations/Internal/MigrationsModelDiffer.cs

@@ -2189,7 +2189,7 @@ private IEnumerable<MigrationOperation> GetDataOperations(
         var commandBatches = new CommandBatchPreparer(CommandBatchPreparerDependencies)
             .BatchCommands(entries, updateAdapter);
 
-        foreach (var commandBatch in commandBatches)
+        foreach (var (commandBatch, _) in commandBatches)
         {
             InsertDataOperation? batchInsertOperation = null;
             foreach (var command in commandBatch.ModificationCommands)

src/EFCore.Relational/Properties/RelationalStrings.resx

@@ -669,6 +669,12 @@
   <data name="MissingParameterValue" xml:space="preserve">
     <value>No value was provided for the required parameter '{parameter}'.</value>
   </data>
+  <data name="ModificationCommandBatchAlreadyComplete" xml:space="preserve">
+    <value>Cannot add commands to a completed ModificationCommandBatch.</value>
+  </data>
+  <data name="ModificationCommandBatchNotComplete" xml:space="preserve">
+    <value>Cannot execute an ModificationCommandBatch which hasn't been completed.</value>
+  </data>
   <data name="ModificationCommandInvalidEntityState" xml:space="preserve">
     <value>Cannot save changes for an entity of type '{entityType}' in state '{entityState}'. This may indicate a bug in Entity Framework, please open an issue at https://go.microsoft.com/fwlink/?linkid=2142044. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the key values of the entity.</value>
   </data>

src/EFCore.Relational/Update/IBatchExecutor.cs

@@ -28,17 +28,21 @@ public interface IBatchExecutor
     /// <summary>
     ///     Executes the commands in the batches against the given database connection.
     /// </summary>
-    /// <param name="commandBatches">The batches to execute.</param>
+    /// <param name="commandBatches">
+    ///     A list of value tuples, each of which contains a batch to execute, and whether more batches are available.
+    /// </param>
     /// <param name="connection">The database connection to use.</param>
     /// <returns>The total number of rows affected.</returns>
     int Execute(
-        IEnumerable<ModificationCommandBatch> commandBatches,
+        IEnumerable<(ModificationCommandBatch Batch, bool HasMore)> commandBatches,
         IRelationalConnection connection);
 
     /// <summary>
     ///     Executes the commands in the batches against the given database connection.
     /// </summary>
-    /// <param name="commandBatches">The batches to execute.</param>
+    /// <param name="commandBatches">
+    ///     A list of value tuples, each of which contains a batch to execute, and whether more batches are available.
+    /// </param>
     /// <param name="connection">The database connection to use.</param>
     /// <param name="cancellationToken">A <see cref="CancellationToken" /> to observe while waiting for the task to complete.</param>
     /// <returns>
@@ -47,7 +51,7 @@ int Execute(
     /// </returns>
     /// <exception cref="OperationCanceledException">If the <see cref="CancellationToken" /> is canceled.</exception>
     Task<int> ExecuteAsync(
-        IEnumerable<ModificationCommandBatch> commandBatches,
+        IEnumerable<(ModificationCommandBatch Batch, bool HasMore)> commandBatches,
         IRelationalConnection connection,
         CancellationToken cancellationToken = default);
 }

src/EFCore.Relational/Update/ICommandBatchPreparer.cs

@@ -32,8 +32,6 @@ public interface ICommandBatchPreparer
     /// </summary>
     /// <param name="entries">The entries that represent the entities to be modified.</param>
     /// <param name="updateAdapter">The model data.</param>
-    /// <returns>The list of batches to execute.</returns>
-    IEnumerable<ModificationCommandBatch> BatchCommands(
-        IList<IUpdateEntry> entries,
-        IUpdateAdapter updateAdapter);
+    /// <returns>A list of value tuples, each of which contains a batch to execute, and whether more batches are available.</returns>
+    IEnumerable<(ModificationCommandBatch Batch, bool HasMore)> BatchCommands(IList<IUpdateEntry> entries, IUpdateAdapter updateAdapter);
 }

src/EFCore.Relational/Update/IUpdateSqlGenerator.cs

@@ -54,6 +54,26 @@ void AppendNextSequenceValueOperation(
     /// <param name="commandStringBuilder">The builder to which the SQL fragment should be appended.</param>
     void AppendBatchHeader(StringBuilder commandStringBuilder);
 
+    /// <summary>
+    ///     Prepends a SQL command for turning on autocommit mode in the database, in case it is off.
+    /// </summary>
+    /// <param name="commandStringBuilder">The builder to which the SQL should be prepended.</param>
+    void PrependEnsureAutocommit(StringBuilder commandStringBuilder);
+
+    /// <summary>
+    ///     Appends a SQL command for deleting a row to the commands being built.
+    /// </summary>
+    /// <param name="commandStringBuilder">The builder to which the SQL should be appended.</param>
+    /// <param name="command">The command that represents the delete operation.</param>
+    /// <param name="commandPosition">The ordinal of this command in the batch.</param>
+    /// <param name="requiresTransaction">Returns whether the SQL appended must be executed in a transaction to work correctly.</param>
+    /// <returns>The <see cref="ResultSetMapping" /> for the command.</returns>
+    ResultSetMapping AppendDeleteOperation(
+        StringBuilder commandStringBuilder,
+        IReadOnlyModificationCommand command,
+        int commandPosition,
+        out bool requiresTransaction);
+
     /// <summary>
     ///     Appends a SQL command for deleting a row to the commands being built.
     /// </summary>
@@ -64,7 +84,22 @@ void AppendNextSequenceValueOperation(
     ResultSetMapping AppendDeleteOperation(
         StringBuilder commandStringBuilder,
         IReadOnlyModificationCommand command,
-        int commandPosition);
+        int commandPosition)
+        => AppendDeleteOperation(commandStringBuilder, command, commandPosition, out _);
+
+    /// <summary>
+    ///     Appends a SQL command for inserting a row to the commands being built.
+    /// </summary>
+    /// <param name="commandStringBuilder">The builder to which the SQL should be appended.</param>
+    /// <param name="command">The command that represents the delete operation.</param>
+    /// <param name="commandPosition">The ordinal of this command in the batch.</param>
+    /// <param name="requiresTransaction">Returns whether the SQL appended must be executed in a transaction to work correctly.</param>
+    /// <returns>The <see cref="ResultSetMapping" /> for the command.</returns>
+    ResultSetMapping AppendInsertOperation(
+        StringBuilder commandStringBuilder,
+        IReadOnlyModificationCommand command,
+        int commandPosition,
+        out bool requiresTransaction);
 
     /// <summary>
     ///     Appends a SQL command for inserting a row to the commands being built.
@@ -76,7 +111,22 @@ ResultSetMapping AppendDeleteOperation(
     ResultSetMapping AppendInsertOperation(
         StringBuilder commandStringBuilder,
         IReadOnlyModificationCommand command,
-        int commandPosition);
+        int commandPosition)
+        => AppendInsertOperation(commandStringBuilder, command, commandPosition, out _);
+
+    /// <summary>
+    ///     Appends a SQL command for updating a row to the commands being built.
+    /// </summary>
+    /// <param name="commandStringBuilder">The builder to which the SQL should be appended.</param>
+    /// <param name="command">The command that represents the delete operation.</param>
+    /// <param name="commandPosition">The ordinal of this command in the batch.</param>
+    /// <param name="requiresTransaction">Returns whether the SQL appended must be executed in a transaction to work correctly.</param>
+    /// <returns>The <see cref="ResultSetMapping" /> for the command.</returns>
+    ResultSetMapping AppendUpdateOperation(
+        StringBuilder commandStringBuilder,
+        IReadOnlyModificationCommand command,
+        int commandPosition,
+        out bool requiresTransaction);
 
     /// <summary>
     ///     Appends a SQL command for updating a row to the commands being built.
@@ -88,5 +138,6 @@ ResultSetMapping AppendInsertOperation(
     ResultSetMapping AppendUpdateOperation(
         StringBuilder commandStringBuilder,
         IReadOnlyModificationCommand command,
-        int commandPosition);
+        int commandPosition)
+        => AppendUpdateOperation(commandStringBuilder, command, commandPosition, out _);
 }

src/EFCore.Relational/Update/Internal/BatchExecutor.cs

@@ -49,9 +49,18 @@ public BatchExecutor(
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public virtual int Execute(
-        IEnumerable<ModificationCommandBatch> commandBatches,
+        IEnumerable<(ModificationCommandBatch Batch, bool HasMore)> commandBatches,
         IRelationalConnection connection)
     {
+        using var batchEnumerator = commandBatches.GetEnumerator();
+
+        if (!batchEnumerator.MoveNext())
+        {
+            return 0;
+        }
+
+        var (batch, hasMoreBatches) = batchEnumerator.Current;
+
         var rowsAffected = 0;
         var transaction = connection.CurrentTransaction;
         var beganTransaction = false;
@@ -62,7 +71,9 @@ public virtual int Execute(
             if (transaction == null
                 && transactionEnlistManager?.EnlistedTransaction is null
                 && transactionEnlistManager?.CurrentAmbientTransaction is null
-                && CurrentContext.Context.Database.AutoTransactionsEnabled)
+                && CurrentContext.Context.Database.AutoTransactionsEnabled
+                // Don't start a transaction if we have a single batch which doesn't require a transaction (single command), for perf.
+                && (hasMoreBatches || batch.RequiresTransaction))
             {
                 transaction = connection.BeginTransaction();
                 beganTransaction = true;
@@ -79,11 +90,13 @@ public virtual int Execute(
                 }
             }
 
-            foreach (var batch in commandBatches)
+            do
             {
+                batch = batchEnumerator.Current.Batch;
                 batch.Execute(connection);
                 rowsAffected += batch.ModificationCommands.Count;
             }
+            while (batchEnumerator.MoveNext());
 
             if (beganTransaction)
             {
@@ -143,10 +156,19 @@ public virtual int Execute(
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public virtual async Task<int> ExecuteAsync(
-        IEnumerable<ModificationCommandBatch> commandBatches,
+        IEnumerable<(ModificationCommandBatch Batch, bool HasMore)> commandBatches,
         IRelationalConnection connection,
         CancellationToken cancellationToken = default)
     {
+        using var batchEnumerator = commandBatches.GetEnumerator();
+
+        if (!batchEnumerator.MoveNext())
+        {
+            return 0;
+        }
+
+        var (batch, hasMoreBatches) = batchEnumerator.Current;
+
         var rowsAffected = 0;
         var transaction = connection.CurrentTransaction;
         var beganTransaction = false;
@@ -157,7 +179,9 @@ public virtual async Task<int> ExecuteAsync(
             if (transaction == null
                 && transactionEnlistManager?.EnlistedTransaction is null
                 && transactionEnlistManager?.CurrentAmbientTransaction is null
-                && CurrentContext.Context.Database.AutoTransactionsEnabled)
+                && CurrentContext.Context.Database.AutoTransactionsEnabled
+                // Don't start a transaction if we have a single batch which doesn't require a transaction (single command), for perf.
+                && (hasMoreBatches || batch.RequiresTransaction))
             {
                 transaction = await connection.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                 beganTransaction = true;
@@ -174,11 +198,13 @@ public virtual async Task<int> ExecuteAsync(
                 }
             }
 
-            foreach (var batch in commandBatches)
+            do
             {
+                batch = batchEnumerator.Current.Batch;
                 await batch.ExecuteAsync(connection, cancellationToken).ConfigureAwait(false);
                 rowsAffected += batch.ModificationCommands.Count;
             }
+            while (batchEnumerator.MoveNext());
 
             if (beganTransaction)
             {

src/EFCore.Relational/Update/Internal/CommandBatchPreparer.cs

@@ -50,16 +50,18 @@ public CommandBatchPreparer(CommandBatchPreparerDependencies dependencies)
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    public virtual IEnumerable<ModificationCommandBatch> BatchCommands(
+    public virtual IEnumerable<(ModificationCommandBatch Batch, bool HasMore)> BatchCommands(
         IList<IUpdateEntry> entries,
         IUpdateAdapter updateAdapter)
     {
         var parameterNameGenerator = Dependencies.ParameterNameGeneratorFactory.Create();
         var commands = CreateModificationCommands(entries, updateAdapter, parameterNameGenerator.GenerateNext);
         var sortedCommandSets = TopologicalSort(commands);
 
-        foreach (var independentCommandSet in sortedCommandSets)
+        for (var commandSetIndex = 0; commandSetIndex < sortedCommandSets.Count; commandSetIndex++)
         {
+            var independentCommandSet = sortedCommandSets[commandSetIndex];
+
             independentCommandSet.Sort(Dependencies.ModificationCommandComparer);
 
             var batch = Dependencies.ModificationCommandBatchFactory.Create();
@@ -83,7 +85,9 @@ public virtual IEnumerable<ModificationCommandBatch> BatchCommands(
                                 batch.ModificationCommands.SelectMany(c => c.Entries), batch.ModificationCommands.Count);
                         }
 
-                        yield return batch;
+                        batch.Complete();
+
+                        yield return (batch, true);
                     }
                     else
                     {
@@ -92,14 +96,19 @@ public virtual IEnumerable<ModificationCommandBatch> BatchCommands(
 
                         foreach (var command in batch.ModificationCommands)
                         {
-                            yield return StartNewBatch(parameterNameGenerator, command);
+                            batch = StartNewBatch(parameterNameGenerator, command);
+                            batch.Complete();
+
+                            yield return (batch, true);
                         }
                     }
 
                     batch = StartNewBatch(parameterNameGenerator, modificationCommand);
                 }
             }
 
+            var hasMoreCommandSets = commandSetIndex < sortedCommandSets.Count - 1;
+
             if (batch.ModificationCommands.Count == 1
                 || batch.ModificationCommands.Count >= _minBatchSize)
             {
@@ -109,16 +118,21 @@ public virtual IEnumerable<ModificationCommandBatch> BatchCommands(
                         batch.ModificationCommands.SelectMany(c => c.Entries), batch.ModificationCommands.Count);
                 }
 
-                yield return batch;
+                batch.Complete();
+
+                yield return (batch, hasMoreCommandSets);
             }
             else
             {
                 Dependencies.UpdateLogger.BatchSmallerThanMinBatchSize(
                     batch.ModificationCommands.SelectMany(c => c.Entries), batch.ModificationCommands.Count, _minBatchSize);
 
-                foreach (var command in batch.ModificationCommands)
+                for (var commandIndex = 0; commandIndex < batch.ModificationCommands.Count; commandIndex++)
                 {
-                    yield return StartNewBatch(parameterNameGenerator, command);
+                    var singleCommandBatch = StartNewBatch(parameterNameGenerator, batch.ModificationCommands[commandIndex]);
+                    singleCommandBatch.Complete();
+
+                    yield return (singleCommandBatch, hasMoreCommandSets || commandIndex < batch.ModificationCommands.Count - 1);
                 }
             }
         }

src/EFCore.Relational/Update/ModificationCommandBatch.cs

@@ -33,6 +33,16 @@ public abstract class ModificationCommandBatch
     /// </returns>
     public abstract bool AddCommand(IReadOnlyModificationCommand modificationCommand);
 
+    /// <summary>
+    ///     Indicates that no more commands will be added to this batch, and prepares it for execution.
+    /// </summary>
+    public abstract void Complete();
+
+    /// <summary>
+    ///     Indicates whether the batch requires a transaction in order to execute correctly.
+    /// </summary>
+    public abstract bool RequiresTransaction { get; }
+
     /// <summary>
     ///     Sends insert/update/delete commands to the database.
     /// </summary>