When Did My Azure SQL Database Server Restart?

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Getting the server restart time for an on-premise SQL Server is simple, and in fact there are several ways using sys.dm_os_sys_info, sys.dm_exec_sessions, sys.traces, or sys.databases

In an Azure SQL Database, you don’t get access to those system objects.

Brent Ozar posted a way to get the approximate Azure SQL Database restart date/time but I found that some of the wait types can produce large outliers and skew the result:

Instead, I’ve modified to use a standard statistics technique to reject outlier values that are outside 1.5 times the interquartile range:

;with cte as
(
    SELECT wait_time_ms 
    FROM sys.dm_os_wait_stats w with(nolock)
    WHERE wait_type IN 
    (
        'BROKER_TASK_STOP',
        'DIRTY_PAGE_POLL',
        'HADR_FILESTREAM_IOMGR_IOCOMPLETION',
        'LAZYWRITER_SLEEP',
        'LOGMGR_QUEUE',
        'REQUEST_FOR_DEADLOCK_SEARCH',
        'XE_DISPATCHER_WAIT',
        'XE_TIMER_EVENT'
    )
)
select 
    approx_ms_since_restart = AVG(wait_time_ms), 
    approximate_restart_date = DATEADD(s, AVG(-wait_time_ms)/1000, GETDATE())
from 
cte
cross join
     (select 
         q1 = min(wait_time_ms), 
         q3 = max(wait_time_ms), 
         iqr = max(wait_time_ms) - min(wait_time_ms)
      from (select 
               wait_time_ms,
               row_number() over (order by wait_time_ms) as seqnum,
               count(*) over (partition by null) as total
            from cte
           ) t
      where seqnum = cast(total * 0.25 as int) or seqnum = cast(total * 0.75 as int)
     ) qts
 where (wait_time_ms >= q1 - 1.5 * iqr) AND (wait_time_ms <= q3 + 1.5 * iqr)

This tells me my Azure server restarted on the 21st Sept 2018 around 23:46.

It’s not as complicated as it first looks:

The first part is obviously the same as Brent Ozar’s query, it gets a list of waits and their respective cumulative wait times. We generate a row number ordered by wait time and the total number of rows, and then pick 2 values using the row number at positions a quarter and three quarters along that list (the first and third quartile values). We then reject any value that is smaller than the 1st quartile value minus 1.5 times the interquartile range and any value that is larger than the 3rd quartile value plus 1.5 times the interquartile range.

Note: DATEADD() only accepts an integer for its second parameter, and using milliseconds(ms) overflows for even short periods of server up-time. In fact, since it’s approximate it might be better to use:

approximate_restart_date = DATEADD(minute, AVG(-wait_time_ms)/60000, GETDATE())

SQL Server 2019 …

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If anyone needed a single concrete reason to upgrade to SQL Server 2019 (when its released), ignoring all the new features, here it is:

2628 – String or binary data would be truncated in table ‘%.ls’, column ‘%.ls’. Truncated value: ‘%.*ls’.

That’s right! After something like 25+ years, Microsoft are finally fixing the cursed “BINARY OR STRING DATA WOULD BE TRUNCATED”!

Seen via Brent Ozar’s post: What’s New in SQL Server 2019’s sys.messages: More Unannounced Features

Set Up SQL Server Agent Alerts

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SQL Server alerts are a free and easy way to get notified of corruption, agent job failures, or major failures before you get angry phone calls from users.

You should have already set up Database Mail and an alert operator to receive notifications. TIP: Always use an email distribution list for your operator notification email. If you use a person’s email, they might change jobs, or be on holiday…

The script below sets up the standard SQL Server Agent alerts for severity 17 through 25 as well as specific alerts for 823, 824 and 825 errors, and a bunch of others:


USE [msdb];
GO
 
SET NOCOUNT ON;

BEGIN TRANSACTION
 
 -- Change these as required...
DECLARE @Normal_Delay_Between_Responses int = 900   -- in seconds
DECLARE @Medium_Delay_Between_Responses int = 3600 
DECLARE @Long_Delay_Between_Responses int   = 14400 
DECLARE @OperatorName sysname = N'SQLDBAGroup'
DECLARE @CategoryName sysname = N'SQL Server Agent Alerts';

DECLARE @DelayBetweenResponses int
    
DECLARE @TotalAlerts int
DECLARE @Row int = 1
DECLARE @AlertName sysname
DECLARE @SeverityNo int
DECLARE @ErrorNo int
 
DECLARE @Alerts TABLE
(
    Id int IDENTITY(1,1) NOT NULL
    ,SeverityNo int NULL
    ,ErrorNo int NULL
    ,AlertName sysname NOT NULL
    ,DelayBetweenResponses int NOT NULL
);
 
INSERT @Alerts (SeverityNo, AlertName, DelayBetweenResponses) 
VALUES
     (17, 'Alert - Sev 17 - Insufficient Resources', @Normal_DELAY_BETWEEN_RESPONSES)
    ,(18, 'Alert - Sev 18 - Nonfatal Internal Error', @Normal_DELAY_BETWEEN_RESPONSES)
    ,(19, 'Alert - Sev 19 - Fatal Error in Resource', @Normal_Delay_Between_Responses)
    ,(20, 'Alert - Sev 20 - Fatal Error in Current Process', @Normal_Delay_Between_Responses)
    ,(21, 'Alert - Sev 21 - Fatal Error in Database Process', @Normal_Delay_Between_Responses)
    ,(22, 'Alert - Sev 22 - Fatal Error: Table Integrity Suspect', @Normal_Delay_Between_Responses)
    ,(23, 'Alert - Sev 23 - Fatal Error: Database Integrity Suspect', @Normal_Delay_Between_Responses)
    ,(24, 'Alert - Sev 24 - Fatal Error: Hardware Error', @Normal_Delay_Between_Responses)
    ,(25, 'Alert - Sev 25 - Fatal Error', @Normal_Delay_Between_Responses);
 
INSERT @Alerts (ErrorNo, AlertName, DelayBetweenResponses) 
VALUES
     (601,  'Alert - Error 601 - NOLOCK scan aborted due to data movement', @Long_Delay_Between_Responses)
    ,(674,  'Alert - Error 674 - Exception occurred in destructor', @Long_Delay_Between_Responses)
    ,(708,  'Alert - Error 708 - Low virtual address space or low virtual memory', @Medium_Delay_Between_Responses)
    ,(806,  'Alert - Error 806 - Audit failure: page read from disk failed basic integrity checks', @Medium_Delay_Between_Responses)

    ,(823,  'Alert - Error 823 - I/O Error: http://support.microsoft.com/kb/2015755', @Normal_Delay_Between_Responses)
    ,(824,  'Alert - Error 824 - Consistency-based I/O error: http://support.microsoft.com/kb/2015756', @Normal_Delay_Between_Responses)
    ,(825,  'Alert - Error 825 - File Read Retry: http://support.microsoft.com/kb/2015757', @Normal_Delay_Between_Responses)
    ,(832,  'Alert - Error 832 - Constant page has changed: http://support.microsoft.com/kb/2015759', @Normal_Delay_Between_Responses)
    ,(833,  'Alert - Error 833 - Long I/O request', @Long_Delay_Between_Responses)

    ,(855,  'Alert - Error 855 - Uncorrectable hardware memory corruption detected', @Normal_Delay_Between_Responses)
    ,(856,  'Alert - Error 856 - SQL Server has detected hardware memory corruption, but has recovered the page', @Normal_Delay_Between_Responses)

    ,(1205, 'Alert - Error 1205 - Transaction Deadlock arbitrated', @Long_Delay_Between_Responses)

    ,(3401, 'Alert - Error 3401 - Errors occurred during recovery while rolling back a transaction', @Normal_Delay_Between_Responses)
    ,(3410, 'Alert - Error 3410 - Data in filegroup is offline', @Medium_Delay_Between_Responses)
    ,(3414, 'Alert - Error 3414 - Recovery Error', @Long_Delay_Between_Responses)
    ,(3422, 'Alert - Error 3422 - Database was shutdown', @Long_Delay_Between_Responses)
    ,(3452, 'Alert - Error 3452 - Recovery inconsistency', @Long_Delay_Between_Responses)
    ,(3619, 'Alert - Error 3619 - Could not write a checkpoint because the log is out of space', @Medium_Delay_Between_Responses)
    ,(3620, 'Alert - Error 3620 - Automatic checkpointing is disabled because the log is out of space', @Medium_Delay_Between_Responses)
    ,(3959, 'Alert - Error 3959 - Version store is full', @Normal_Delay_Between_Responses)
    ,(5029, 'Alert - Error 5029 - Warning: Log has been rebuilt', @Long_Delay_Between_Responses)
    ,(5144, 'Alert - Error 5144 - Autogrow of file was cancelled by user or timed out', @Long_Delay_Between_Responses)
    ,(5145, 'Alert - Error 5145 - Long Autogrow of file', @Medium_Delay_Between_Responses)
    ,(5182, 'Alert - Error 5182 - New log file created', @Long_Delay_Between_Responses)
    ,(9001, 'Alert - Error 9001 - Transaction log not available', @Normal_Delay_Between_Responses)
    ,(9002, 'Alert - Error 9002 - Transaction log full', @Normal_Delay_Between_Responses)
    ,(17173, 'Alert - Error 17173 - Ignored trace flag', @Long_Delay_Between_Responses)
    ,(17883, 'Alert - Error 17883 - Non-yielding Worker on Scheduler', @Medium_Delay_Between_Responses)
    ,(17884, 'Alert - Error 17884 - New queries assigned to process have not been picked up by a worker thread', @Medium_Delay_Between_Responses)
    ,(17887, 'Alert - Error 17887 - Worker appears to be non-yielding on Node', @Medium_Delay_Between_Responses)
    ,(17888, 'Alert - Error 17888 - All schedulers on Node appear deadlocked', @Medium_Delay_Between_Responses)
    ,(17890, 'Alert - Error 17890 - A significant part of sql server process memory has been paged out', @Long_Delay_Between_Responses)
    ,(17891, 'Alert - Error 17891 - Worker appears to be non-yielding on Node', @Medium_Delay_Between_Responses)

SELECT @TotalAlerts = COUNT(*) FROM @Alerts

IF NOT EXISTS(SELECT * FROM msdb.dbo.sysoperators WHERE name = @OperatorName)
BEGIN
    RAISERROR ('SQL Operator %s does not exist', 18, 16, @OperatorName);
    RETURN;
END
 
IF NOT EXISTS (SELECT * FROM msdb.dbo.syscategories
               WHERE category_class = 2  -- ALERT
               AND category_type = 3 AND name = @CategoryName)
BEGIN
    EXEC dbo.sp_add_category @class = N'ALERT', @type = N'NONE', @name = @CategoryName;
END
 
BEGIN TRY
 
    WHILE @Row <= @TotalAlerts 
    BEGIN
 
        SELECT
             @AlertName = @@SERVERNAME + ' - ' + AlertName 
            ,@SeverityNo = SeverityNo
            ,@ErrorNo = ErrorNo
            ,@DelayBetweenResponses = DelayBetweenResponses
        FROM
            @Alerts
        WHERE
            Id = @Row
 
        IF EXISTS (SELECT * FROM msdb.dbo.sysalerts WHERE [name] = @AlertName) 
        BEGIN
            EXEC msdb.dbo.sp_delete_alert @name = @AlertName
        END
 
        IF @SeverityNo IS NOT NULL 
        BEGIN
            EXEC msdb.dbo.sp_add_alert 
                @name = @AlertName,
                @message_id = 0, 
                @severity = @SeverityNo, 
                @enabled = 1, 
                @Delay_Between_Responses = @DelayBetweenResponses, 
                @include_event_description_in = 1, 
                @category_name = @CategoryName, 
                @job_id = N'00000000-0000-0000-0000-000000000000'
        END
 
        IF @ErrorNo IS NOT NULL 
        BEGIN
            -- Errors 855 and 856 require SQL Server 2012+ and Enterprise Edition
            -- [Also need Windows Server 2012+, and hardware that supports memory error correction]
            IF @ErrorNo NOT IN (855, 856) 
               OR (LEFT(CONVERT(CHAR(2),SERVERPROPERTY('ProductVersion')), 2) >= '11' AND SERVERPROPERTY('EngineEdition') = 3)
            BEGIN
                EXEC msdb.dbo.sp_add_alert 
                    @name = @AlertName,
                    @message_id = @ErrorNo, 
                    @severity = 0, 
                    @enabled = 1, 
                    @Delay_Between_Responses = @DelayBetweenResponses, 
                    @include_event_description_in = 1, 
                    @category_name = @CategoryName, 
                    @job_id = N'00000000-0000-0000-0000-000000000000'
            END
        END
 
        EXEC msdb.dbo.sp_add_notification @Alert_Name = @AlertName, @Operator_Name = @OperatorName, @notification_method = 1
 
        SELECT @Row = @Row + 1

    END

END TRY

BEGIN CATCH
    PRINT ERROR_MESSAGE()
 
    IF @@TRANCOUNT > 0 
    BEGIN
        ROLLBACK
    END
END CATCH
 
IF @@TRANCOUNT > 0 
BEGIN
    COMMIT
END

C# : Get Public IP Address

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Posting this code snippet, so I don’t forget it!


    public static string GetPublicIPAddress()
    {
        string result = string.Empty;

        // List of public URLs to be tried in order
        string[] checkIPUrl =
        {
            "https://ipinfo.io/ip",
            "https://checkip.amazonaws.com/",
            "https://api.ipify.org",
            "https://icanhazip.com",
            "https://wtfismyip.com/text"
        };

        using (var client = new WebClient())
        {
            client.Headers["User-Agent"] = "Mozilla/4.0 (Compatible; Windows NT 5.1; MSIE 6.0) " +
                "(compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";

            foreach (var url in checkIPUrl)
            {
                try
                {
                    result = client.DownloadString(url);
                }
                catch
                {
                    // Ignore errors 
                }

                if (!string.IsNullOrEmpty(result))
                    break;
            }
        }

        return result.Replace("\n", "").Trim();
    }

Azure Queues: Retry Poison Messages

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Currently, the Microsoft Azure Storage Explorer doesn’t have the ability to move messages from one Azure queue to another. During development, I sometimes need to retry messages that are in the poison message queue. A poison message is a message that has exceeded the maximum number of delivery attempts to the application. This happens when a queue-based application cannot process a message because of errors.

It’s not difficult to write, but thought it might save someone a few minutes, so I’m posting it here. You’ll need to add a NuGet package reference to Microsoft.NET.Sdk.Functions


using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Queue;

void Main()
{
    const string queuename = "MyQueueName";

    string storageAccountString = "xxxxxx";

    RetryPoisonMesssages(storageAccountString, queuename);
}

private static int RetryPoisonMesssages(string storageAccountString, string queuename)
{
    CloudQueue targetqueue = GetCloudQueueRef(storageAccountString, queuename);
    CloudQueue poisonqueue = GetCloudQueueRef(storageAccountString, queuename + "-poison");

    int count = 0;
    while (true)
    {
        var msg = poisonqueue.GetMessage();
        if (msg == null)
            break;

        poisonqueue.DeleteMessage(msg);
        targetqueue.AddMessage(msg);
        count++;
    }

    return count;
}

private static CloudQueue GetCloudQueueRef(string storageAccountString, string queuename)
{
    CloudStorageAccount storageAccount = CloudStorageAccount.Parse(storageAccountString);
    CloudQueueClient queueClient = storageAccount.CreateCloudQueueClient();
    CloudQueue queue = queueClient.GetQueueReference(queuename);

    return queue;
}

Does the Microsoft CSP RSA provider support a maximum of 2048 bits?

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It seems that the maximum Microsoft’s RSA provider supports is 2048 bits: Is there a limit for RSA key exponents in .NET?

I’ve just been been experimenting with 3072 and 4096 bit keys without success. Error message is “Bad Data” !

Nice one Microsoft! Thanks for you concern about security!

Surprising since NIST’s recommendations are that 3072 bit keys are required “if security is required beyond 2030”

SQL Server Availability Groups: Add ‘Check if Primary’ Step to Existing Agent Jobs

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I’ve recently been helping a client set up and configure SQL Server Always On Availability Groups. In addition to implementing your SQL Server Agent jobs on all the secondaries, you also have to implement a mechanism to make jobs aware of which node they are running on (Primary or secondary replicas). You would think this would be available out of the box, right? I guess they are so many permutations (especially when you have multiple availability groups on the same server), that it was left to end users to implement.

When SQL Server completes a primary <=> secondary replica role change it fires alert 1480, and you can configure this alert to notify you of the role change and act upon it.

You have 2 choices:

  1. Respond to the role changeover alert (1480) and run a task to disable the jobs related to the databases in the availability group that has failed over.
  2. Add a new first job step to every SQL Agent job which checks if it is running on the Primary Replica. If it is running on the Primary then move to the next job step and continue executing the job, otherwise if it is running on a Secondary Replica then stop the job.

To check if the Primary Replica of a given AG database is currently hosted on a particular server or not, you can either check based on the name of the database or you can check based on the name of the Availability Group the database is in (a database can only be in one availability group).

My scenario had a single availability group with not all databases on the server in the AG (a common scenario). After a couple of unsatisfactory attempts at (a), I decided to opt for (b).

Not wanting to do this change manually for every agent job, I’ve created a stored procedure that adds a new first job step to any agent job, to check if the job is running on the primary. If not, it silently quits with success. There’s also a short snippet of TSQL to run the proc for every SQL Agent job.

use master
go

-- Adds a first step to specified job, which checks whether running on Primary replica

create procedure AddAGPrimaryCheckStepToAgentJob
    @jobname nvarchar(128)
as

set nocount on;

-- Do nothing if No AG groups defined
IF SERVERPROPERTY ('IsHadrEnabled') = 1
begin
    declare @jobid uniqueidentifier = (select sj.job_id from msdb.dbo.sysjobs sj where sj.name = @jobname)

    if not exists(select * from msdb.dbo.sysjobsteps where job_id = @jobid and step_name = 'Check If AG Primary' )
    begin
        -- Add new first step: on success go to next step, on failure quit reporting success
        exec msdb.dbo.sp_add_jobstep 
          @job_id = @jobid
        , @step_id = 1
        , @cmdexec_success_code = 0
        , @step_name = 'Check If AG Primary' 
        , @on_success_action = 3  -- On success, go to Next Step
        , @on_success_step_id = 2
        , @on_fail_action = 1     -- On failure, Quit with Success  
        , @on_fail_step_id = 0
        , @retry_attempts = 0
        , @retry_interval = 0
        , @os_run_priority = 0
        , @subsystem = N'TSQL' 
        , @command=N'IF (SELECT ars.role_desc
        FROM sys.dm_hadr_availability_replica_states ars
        JOIN sys.availability_groups ag ON ars.group_id = ag.group_id AND ars.is_local = 1) <> ''Primary''
    BEGIN
       -- Secondary node, throw an error
       raiserror (''Not the AG primary'', 2, 1)
    END'
        , @database_name=N'master'
        , @flags=0
    end
end
GO

-------------------

-- Run AddAGPrimaryCheckStepToAgentJob for each agent job

DECLARE @jobName NVARCHAR(128)

DECLARE jobCursor CURSOR LOCAL FAST_FORWARD
FOR
    SELECT j.name FROM msdb.dbo.sysjobs j
    --WHERE ??? -- filter out any jobs here

OPEN jobCursor 
FETCH NEXT FROM jobCursor INTO @jobName

WHILE @@FETCH_STATUS = 0
BEGIN
    exec AddAGPrimaryCheckStepToAgentJob @jobName

    FETCH NEXT FROM jobCursor INTO @jobName
END

CLOSE jobCursor
DEALLOCATE jobCursor
GO

----------------------

-- Remove the first job step ''Check If AG Primary'' added in previous snippet
-- Just here should you want to remove the step added in snippet above.

DECLARE @jobName NVARCHAR(128)

DECLARE jobCursor CURSOR LOCAL FAST_FORWARD
FOR
    SELECT j.name FROM msdb.dbo.sysjobs j
    join msdb.dbo.sysjobsteps js on js.job_id = j.job_id
    where js.step_name = 'Check If AG Primary' and js.step_id = 1

OPEN jobCursor 
FETCH NEXT FROM jobCursor INTO @jobName

WHILE @@FETCH_STATUS = 0
BEGIN
    
    EXEC msdb.dbo.sp_delete_jobstep  
        @job_name = @jobName,  
        @step_id = 1 ;  
    
    FETCH NEXT FROM jobCursor INTO @jobName
END

CLOSE jobCursor
DEALLOCATE jobCursor
GO

Note: For SQL Server 2014 onwards you can use the builtin function sys.fn_hadr_is_primary_replica('dbname'):

If sys.fn_hadr_is_primary_replica (@dbname) <> 1   
BEGIN  
    -- This is not the primary replica, exit without error. 
END  
-- This is the primary replica, continue to run the job...

C#: Simple Read/Write Application Settings

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I needed a simple C# class for saving writable application settings. The first attempt was to use Project -> Properties -> Settings, but only user scoped settings are writable. Here’s a simple solution: you will need to add Newtonsoft’s Json.NET (Nuget Json.Net) to your project, if you are not already using it.

using System.IO;
using Newtonsoft.Json;
...

public class AppSettingsBase<T> where T : new()
{
    private const string DefaultSettingsFilename = "settings.json";

    public void Save(string fileName = DefaultSettingsFilename)
    {
        File.WriteAllText(fileName, JsonConvert.SerializeObject(this));
    }

    public static void Save(T settings, string fileName = DefaultSettingsFilename)
    {
        File.WriteAllText(fileName, JsonConvert.SerializeObject(settings));
    }

    public static T Load(string fileName = DefaultSettingsFilename)
    {
        return (File.Exists(fileName)) 
            ? JsonConvert.DeserializeObject<T>(File.ReadAllText(fileName)) : new T();
    }
}

Add your application defined settings to your settings class (derived from the base template):

public class AppSettings : AppSettingsBase<AppSettings>
{
    public Guid ClientId = Guid.Empty;
    public List<string> ServerList = new List<string>();
    public List<string> DatabasesToExclude = new List<string>();

    public bool IsAutoUpdate = true;
    public int AutoUpdaterCheckIntervalHours = 6; 
    public DateTime LastUpdateCheckTime = DateTime.MinValue;

    ...
}

Using your settings is simple:

    AppSettings settings = AppSettings.Load();

    settings.LastUpdateCheckTime = DateTime.UtcNow;
    settings.Save();

Create a Single .NET Executable with Multiple Assemblies

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If you want to create a single .NET executable there are several possibilities. In the past I’ve used Jeffrey Richter’s technique of embedding DLLs as resources and loading these into memory from the Manifest Resource Stream on startup. While this works well, it does require a bit of extra code to not try to access anything in an assembly until after it’s been loaded at startup.

In the interest of cleaner code, I decided to give ILMerge a go.

It’s simple to install ILMerge into your application using NuGet:

PM> Install-Package ilmerge -Version 2.14.1208

To run ILMerge on your release builds, add an AfterBuild section to your default projects .csproj file:

  <Target Name="AfterBuild" Condition=" '(Configuration)' == 'Release' ">     <CreateItem Include="@(ReferenceCopyLocalPaths)" Condition="'%(Extension)'=='.dll'">       <Output ItemName="AssembliesToMerge" TaskParameter="Include" />     </CreateItem>     <PropertyGroup>       <ReferenceAssemblies>C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5.2</ReferenceAssemblies>     </PropertyGroup>     <Message Importance="high" Text="Executing ILMerge...with target platform from(ReferenceAssemblies)" />
    <Exec Command="&quot;(SolutionDir)\packages\ILMerge.2.14.1208\tools\ILMerge.exe" /target:exe /out:@(MainAssembly) /internalize /targetplatform:v4,"(ReferenceAssemblies)&quot; &quot;@(IntermediateAssembly)&quot; @(AssembliesToMerge->'&quot;%(FullPath)&quot;', ' ')" />
    <Delete Files="@(ReferenceCopyLocalPaths->'$(OutDir)%(DestinationSubDirectory)%(Filename)%(Extension)')" />
  </Target>

Note: If you receive this error from ILMerge when building your release executable:

An exception occurred during merging:
ILMerge.Merge: There were errors reported in AWSSDK.Core’s metadata.
Array dimensions exceeded supported range.
at ILMerging.ILMerge.Merge()
at ILMerging.ILMerge.Main(String[] args)

It’s because ILMerge doesn’t currently support the new portable PDB format.
https://github.com/Microsoft/ILMerge/issues/29
https://github.com/Microsoft/ILMerge/issues/11

If you can live without the .pdb files being merged into a single PDB file add /ndebug to the Exec command.

This is a temporary workaround for issues with ILMerge where it cannot process the new portable .NET PDB format.

An excellent resource on PDB files is John Robbins’s : PDB Files: What Every Developer Must Know :

A .NET PDB only contains two pieces of information, the source file names and their lines and the local variable names. All the other information is already in the .NET metadata so there is no need to duplicate the same information in a PDB file.