我有一个带有“SelfRef”表的数据库。SelfRef 有两个字段：
Id (guid, PK, not null)
SelfRefId (guid, nullable)
有一个外键约束将 SelfRefId 字段映射回 Id 字段。
我有一个引用数据库的 EntityFrameworkCore 项目。我正在运行以下测试：
我发现第 2 步经常导致死锁。我不明白为什么应该这样做。
我在下面展示了我的代码，但我怀疑这个问题是特定于这段代码的：
public class TestSelfRefDeadlock
{
private async Task CreateSelfRef_ThenDelete_Deletes() {
var sr = new SelfRef
{
Id = Guid.NewGuid(),
Name = "SR"
};
var factory = new SelfRefDbFactory();
using (var db = factory.Create()) {
db.Add(sr);
await db.SaveChangesAsync(); // EDIT: Changing this to db.SaveChanges() appears to fix the problem, at least in this test scenario.
}
using (var db = factory.Create()) {
db.SelfRef.Remove(sr);
await db.SaveChangesAsync();
}
}
private IEnumerable<Task> DeadlockTasks() {
for (int i=0; i<2; i++) {
yield return CreateSelfRef_ThenDelete_Deletes();
}
}
[Fact]
public async Task LotsaDeletes_DoNotDeadlock()
=> await Task.WhenAll(DeadlockTasks());
}
编辑：我已经确认在 EF6 中发生了同样的死锁。
在我的数据库中创建表：
USE [SelfReferential]
GO
/****** Object: Table [dbo].[SelfRef] Script Date: 3/20/2018 3:43:50 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[SelfRef](
[Id] [uniqueidentifier] NOT NULL,
[SelfReferentialId] [uniqueidentifier] NULL,
[Name] [nchar](10) NULL,
CONSTRAINT [PK_SelfRef] PRIMARY KEY CLUSTERED
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[SelfRef] WITH CHECK ADD CONSTRAINT [FK_SelfRef_SelfRef] FOREIGN KEY([SelfReferentialId])
REFERENCES [dbo].[SelfRef] ([Id])
GO
ALTER TABLE [dbo].[SelfRef] CHECK CONSTRAINT [FK_SelfRef_SelfRef]
GO
生成实体：
Scaffold-DbContext "Server=localhost;Database=SelfReferential;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -Context SelfRefDb -OutputDir Entities -Force
DbFactory 类：
public class SelfRefDbFactory : IFactory<SelfRefDb>
{
private const string str1 = @"Data Source=MyPcName;Initial Catalog=SelfReferential;Integrated Security=True;ApplicationIntent=ReadWrite;";
private const string str2 = @"Data Source=MyPcName;Initial Catalog=SelfReferential;Integrated Security=True;ApplicationIntent=ReadWrite;MultipleActiveResultSets=True";
public SelfRefDb Create() {
var options = new DbContextOptionsBuilder<SelfRefDb>()
.UseSqlServer(str1).Options;
return new SelfRefDb(options);
}
}
错误信息：
Message: System.InvalidOperationException : An exception has been raised that is likely due to a transient failure. If you are connecting to a SQL Azure database consider using SqlAzureExecutionStrategy.
---- Microsoft.EntityFrameworkCore.DbUpdateException : An error occurred while updating the entries. See the inner exception for details.
-------- System.Data.SqlClient.SqlException : Transaction (Process ID 58) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.
下面是分析器中的一些 Sql 事件。我跳过了许多“审核登录”和“审核注销”事件，并且这些字段被一一复制。一定有更好的方法来提取东西，但我不知道它是什么。
exec sp_executesql N'SET NOCOUNT ON;
INSERT INTO [SelfRef] ([Id], [Name], [SelfReferentialId])
VALUES (@p0, @p1, @p2);
',N'@p0 uniqueidentifier,@p1 nvarchar(10),@p2
uniqueidentifier',@p0='93671E2E-28E5-414D-A3DB-239FA433640C',@p1=N'SR',@p2=NULL
这个特殊的运行有两个线程。在上述两个事件之后，我看到了两个：
exec sp_reset_connection
然后两个像这样：
exec sp_executesql N'SET NOCOUNT ON;
DELETE FROM [SelfRef]
WHERE [Id] = @p0;
SELECT @@ROWCOUNT;
',N'@p0 uniqueidentifier',@p0='F5B53458-08C5-485E-8364-2A2842E95158'
再重新连接两次，就大功告成了。
死锁xml：
<deadlock-list>
<deadlock victim="process1fe3db6b468">
<process-list>
<process id="process1fe3db6b468" taskpriority="0" logused="300" waitresource="KEY: 14:72057594041401344 (427c492d0b23)" waittime="147" ownerId="218910" transactionname="user_transaction" lasttranstarted="2018-03-22T14:33:57.880" XDES="0x2021f8bc408" lockMode="S" schedulerid="2" kpid="8540" status="suspended" spid="53" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2018-03-22T14:33:57.883" lastbatchcompleted="2018-03-22T14:33:57.880" lastattention="1900-01-01T00:00:00.880" clientapp=".Net SqlClient Data Provider" hostname="WILLIAMASUS" hostpid="14656" loginname="MicrosoftAccount\jockusch@gmail.com" isolationlevel="read committed (2)" xactid="218910" currentdb="14" lockTimeout="4294967295" clientoption1="673185824" clientoption2="128056">
<executionStack>
<frame procname="adhoc" line="2" stmtstart="78" stmtend="154" sqlhandle="0x0200000087849c297464e5637211740e8fde989bf9ffc37a0000000000000000000000000000000000000000">
unknown </frame>
<frame procname="unknown" line="1" sqlhandle="0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000">
unknown </frame>
</executionStack>
<inputbuf>
(@p0 uniqueidentifier)SET NOCOUNT ON;
DELETE FROM [SelfRef]
WHERE [Id] = @p0;
SELECT @@ROWCOUNT;
</inputbuf>
</process>
<process id="process1fe3db684e8" taskpriority="0" logused="300" waitresource="KEY: 14:72057594041401344 (8e30f77e2707)" waittime="146" ownerId="218908" transactionname="user_transaction" lasttranstarted="2018-03-22T14:33:57.880" XDES="0x20227f6b458" lockMode="S" schedulerid="1" kpid="8300" status="suspended" spid="54" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2018-03-22T14:33:57.883" lastbatchcompleted="2018-03-22T14:33:57.880" lastattention="1900-01-01T00:00:00.880" clientapp=".Net SqlClient Data Provider" hostname="WILLIAMASUS" hostpid="14656" loginname="MicrosoftAccount\jockusch@gmail.com" isolationlevel="read committed (2)" xactid="218908" currentdb="14" lockTimeout="4294967295" clientoption1="673185824" clientoption2="128056">
<executionStack>
<frame procname="adhoc" line="2" stmtstart="78" stmtend="154" sqlhandle="0x0200000087849c297464e5637211740e8fde989bf9ffc37a0000000000000000000000000000000000000000">
unknown </frame>
<frame procname="unknown" line="1" sqlhandle="0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000">
unknown </frame>
</executionStack>
<inputbuf>
(@p0 uniqueidentifier)SET NOCOUNT ON;
DELETE FROM [SelfRef]
WHERE [Id] = @p0;
SELECT @@ROWCOUNT;
</inputbuf>
</process>
</process-list>
<resource-list>
<keylock hobtid="72057594041401344" dbid="14" objectname="SelfReferential.dbo.SelfRef" indexname="PK_SelfRef" id="lock20229074e00" mode="X" associatedObjectId="72057594041401344">
<owner-list>
<owner id="process1fe3db684e8" mode="X"/>
</owner-list>
<waiter-list>
<waiter id="process1fe3db6b468" mode="S" requestType="wait"/>
</waiter-list>
</keylock>
<keylock hobtid="72057594041401344" dbid="14" objectname="SelfReferential.dbo.SelfRef" indexname="PK_SelfRef" id="lock20229073c80" mode="X" associatedObjectId="72057594041401344">
<owner-list>
<owner id="process1fe3db6b468" mode="X"/>
</owner-list>
<waiter-list>
<waiter id="process1fe3db684e8" mode="S" requestType="wait"/>
</waiter-list>
</keylock>
</resource-list>
</deadlock>
</deadlock-list>
死锁 XML 表明两个会话正在争夺两个不同的行，每个会话在其中一个行上具有 e(X) 独占锁，并在另一行上请求 (S) 共享锁。
鉴于：
hostpid）trancount="2"两个会话都显示死锁 XML有可能：
现在，连接池的东西（数字 2）通常不会引起任何问题，但由于在某些情况下它会引起任何问题（例如，如果正在使用分布式事务），我不想排除它。而且，由于我不知道 EF 和/或异步选项如何处理事情，所以它很可能是异步和连接池的组合。
那么，为什么不首先尝试保留步骤 1 的异步保存，而是通过添加Pooling=false;到连接字符串来禁用连接池。
当然，无论禁用连接池是否有帮助，考虑到在保存时不使用异步可以解决问题（或者至少到目前为止似乎如此），您应该考虑在创建项目时不使用异步。也许只将其用于删除和选择？即使我们确定在第 1 步中使用和不使用异步之间行为的确切变化，也可能无法解决任何问题（或者至少在不做可能不应该做的事情的情况下无法解决）。