仅插入新行而不执行任何选择时 SQL Server 死锁

Question

我在我的应用程序中看到持续的死锁，即使它不执行 select 语句、delete 语句和 update 语句。它只是插入全新的数据。

TL;DR：这似乎与外键有关。如果我删除它，那么我根本不会遇到任何死锁。但由于显而易见的原因，这不是一个可接受的解决方案。

鉴于下表结构

CREATE TABLE [dbo].[IncomingFile]
(
    [Id] UNIQUEIDENTIFIER NOT NULL, 
    [ConcurrencyVersion] RowVersion NOT NULL,
    CONSTRAINT [PK_IncomingFile] PRIMARY KEY CLUSTERED([Id])
)
GO

CREATE TABLE [dbo].[IncomingFileEvent]
(
    [Id] UNIQUEIDENTIFIER NOT NULL, 
    [ConcurrencyVersion] RowVersion NOT NULL,
    [IncomingFileId] UNIQUEIDENTIFIER NOT NULL,
    CONSTRAINT [PK_IncomingFileEvent] PRIMARY KEY CLUSTERED([Id]),
    CONSTRAINT [FK_IncomingFileEvent_IncomingFileId]
        FOREIGN KEY ([IncomingFileId])
        REFERENCES [dbo].[IncomingFile] ([Id])
)
GO

当我遇到多个并发任务插入数据时，我总是看到一个死锁。READ_COMMITTED_SNAPSHOT在我的数据库选项中启用（即使我没有阅读）。

这是将重现该问题的代码。如果您没有遇到问题，请增加NumberOfTasksPerCpu程序顶部的常量。

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace SqlServerDeadlockRepro
{
    class Program
    {
        private const int NumberOfTasksPerCpu = 8; // Keep increasing this by one if you do not get a deadlock!
        private const int NumberOfChildRows = 1_000;
        private const string MSSqlConnectionString = "Server=DESKTOP-G05BF1U;Database=EFCoreConcurrencyTest;Trusted_Connection=True;";

        private static int NumberOfConcurrentTasks;

        static async Task Main(string[] args)
        {
            NumberOfConcurrentTasks = Environment.ProcessorCount * NumberOfTasksPerCpu;

            var readySignals = new Queue<ManualResetEvent>();
            var trigger = new ManualResetEvent(false);
            var processingTasks = new List<Task>();
            for (int index = 0; index < NumberOfConcurrentTasks; index++)
            {
                var readySignal = new ManualResetEvent(false);
                readySignals.Enqueue(readySignal);
                var task = CreateDataWithSqlCommand(trigger, readySignal);
                processingTasks.Add(task);
            }
            Console.WriteLine("Waiting for tasks to become ready");
            while (readySignals.Count > 0)
            {
                var readySignalBatch = new List<WaitHandle>();
                for(int readySignalCount = 0; readySignals.Count > 0 && readySignalCount < 64; readySignalCount++)
                {
                    readySignalBatch.Add(readySignals.Dequeue());
                }
                WaitHandle.WaitAll(readySignalBatch.ToArray());
            }
            Console.WriteLine("Saving data");
            var sw = Stopwatch.StartNew();
            trigger.Set();
            await Task.WhenAll(processingTasks.ToArray());
            sw.Stop();
            Console.WriteLine("Finished - " + sw.ElapsedMilliseconds);
        }

        private static int TaskNumber = 0;
        private static async Task CreateDataWithSqlCommand(ManualResetEvent trigger, ManualResetEvent readySignal)
        {
            await Task.Yield();
            using var connection = new SqlConnection(MSSqlConnectionString);
            await connection.OpenAsync().ConfigureAwait(false);
            var transaction = (SqlTransaction)await connection.BeginTransactionAsync(System.Data.IsolationLevel.ReadCommitted).ConfigureAwait(false);

            Console.WriteLine("Task " + Interlocked.Increment(ref TaskNumber) + $" of {NumberOfConcurrentTasks}  ready ");
            readySignal.Set();
            trigger.WaitOne();
            Guid parentId = Guid.NewGuid();
            string fileCommandSql = "insert into IncomingFile (Id) values (@Id)";
            using var fileCommand = new SqlCommand(fileCommandSql, connection, transaction);
            fileCommand.Parameters.Add("@Id", System.Data.SqlDbType.UniqueIdentifier).Value = parentId;
            await fileCommand.ExecuteNonQueryAsync().ConfigureAwait(false);

            using var fileEventCommand = new SqlCommand
            {
                Connection = connection,
                Transaction = transaction
            };
            var commandTextBulder = new StringBuilder("INSERT INTO [IncomingFileEvent] ([Id], [IncomingFileId]) VALUES ");
            for (var i = 1; i <= NumberOfChildRows * 2; i += 2)
            {
                commandTextBulder.Append($"(@p{i}, @p{i + 1})");
                if (i < NumberOfChildRows * 2 - 1)
                    commandTextBulder.Append(',');

                fileEventCommand.Parameters.AddWithValue($"@p{i}", Guid.NewGuid());
                fileEventCommand.Parameters.AddWithValue($"@p{i + 1}", parentId);
            }

            fileEventCommand.CommandText = commandTextBulder.ToString();
            await fileEventCommand.ExecuteNonQueryAsync().ConfigureAwait(false);
            await transaction.CommitAsync().ConfigureAwait(false);
        }
    }
}

更新

还尝试制作主键NONCLUSTERED并CLUSTERED根据当前日期和时间添加索引。

CREATE TABLE [dbo].[IncomingFile]
(
    [Id] UNIQUEIDENTIFIER NOT NULL, 
    [ConcurrencyVersion] RowVersion NOT NULL,
    [CreatedUtc] DateTime2 DEFAULT GETDATE(),
    CONSTRAINT [PK_IncomingFile] PRIMARY KEY NONCLUSTERED([Id])
)
GO
CREATE CLUSTERED INDEX [IX_IncomingFile_CreatedUtc] on [dbo].[IncomingFile]([CreatedUtc])
GO

CREATE TABLE [dbo].[IncomingFileEvent]
(
    [Id] UNIQUEIDENTIFIER NOT NULL, 
    [ConcurrencyVersion] RowVersion NOT NULL,
    [IncomingFileId] UNIQUEIDENTIFIER NOT NULL,
    [CreatedUtc] DateTime2 DEFAULT GETDATE(),
    CONSTRAINT [PK_IncomingFileEvent] PRIMARY KEY NONCLUSTERED([Id]),
    CONSTRAINT [FK_IncomingFileEvent_IncomingFileId]
        FOREIGN KEY ([IncomingFileId])
        REFERENCES [dbo].[IncomingFile] ([Id])
)
GO
CREATE CLUSTERED INDEX [IX_IncomingFileEvent_CreatedUtc] on [dbo].[IncomingFileEvent]([CreatedUtc])
GO

更新 2

我尝试了从这里获取的顺序 guid ，这没有什么区别。

更新 3

好像和外键有关。如果我删除它，那么我根本不会遇到任何死锁。

更新 4

来自 Sql Server 产品组的一些建议的回复已发布在我原来的 github 问题上。

https://github.com/dotnet/efcore/issues/21899#issuecomment-683404734???????

Answer 1

死锁是由于执行计划需要检查引用完整性造成的。IncomingFile当向相关表中插入大量（1K）行时，会执行表的全表扫描IncomingFileEvent。扫描获取在事务持续期间持有的共享表锁，并且当不同会话各自在刚刚插入的行上持有独占行锁IncomingFile并被另一个会话独占行锁阻止时，会导致死锁。

下面是显示这一点的执行计划：

避免死锁的一种方法是在插入查询OPTION (LOOP JOIN)上使用查询提示IncomingFileEvent：

    var commandTextBulder = new StringBuilder("INSERT INTO [IncomingFileEvent] ([Id], [IncomingFileId]) VALUES ");
    for (var i = 1; i <= NumberOfChildRows * 2; i += 2)
    {
        commandTextBulder.Append($"(@p{i}, @p{i + 1})");
        if (i < NumberOfChildRows * 2 - 1)
            commandTextBulder.Append(',');

        fileEventCommand.Parameters.AddWithValue($"@p{i}", Guid.NewGuid());
        fileEventCommand.Parameters.AddWithValue($"@p{i + 1}", parentId);
    }
    commandTextBulder.Append(" OPTION (LOOP JOIN);");

这是带有提示的计划：

另一方面，请考虑将现有主键更改为以下主键。从数据建模的角度（识别关系）来看，这是更正确的，并且将提高插入和选择的性能，因为相关行物理上聚集在一起。

CONSTRAINT [PK_IncomingFileEvent] PRIMARY KEY CLUSTERED(IncomingFileId, Id)