John McCormack's blogs

Distributed Replay Error: Failed to set proper database for the connection

3rd May 2019 By John McCormack Leave a Comment

Distributed Replay Error: Failed to set proper database for the connection – Troubleshooting dreplay.exe

If you see Failed to set proper database for the connection in your replayresult.trc, it is worth looking at the row below it (in profiler).

Check if the TextData for the row below (with the same ReplaySequence) would run from the database listed in the DatabaseName column.

Hint, either its a database that you haven’t restored to your test environment or you have named the databases differently to production. e.g. you have prefixed the names with perf_

https://johnmccormack.it/2016/10/error-dreplay-could-not-find-any-resources-appropriate-for-the-specified-culture-or-the-neutral-culture/

Useful links

Test read intent connections to an AG Listener

19th April 2019 By John McCormack 4 Comments

To test read intent connections to an AG Listener, I prefer to use SQLCMD but you can also test easily using SSMS.

SQLCMD

The -Kreadonly switch is your key to success here but remember to also specify the database using -d. When not set (and with an initial catalog of master for my login), I found I always got the primary instance back during my check. This simple omission cost me hours of troubleshooting work, because I was convinced my listener wasn’t working correctly. In fact, I just wasn’t testing it correctly.

Read/Write Connections
-sqlcmd -S "SQL01-AG1-list" -d WideWorldImporters -E -q "SELECT @@SERVERNAME;"

Read only Connections
-sqlcmd -S "SQL01-AG1-list" -d WideWorldImporters-E -q "SELECT @@SERVERNAME;" -Kreadonly

The instance that you are connected to will show in the command prompt. Type exit to leave sqlcmd.

SSMS

In object explorer, click Connect and choose Database Engine.

Then, in the bottom right hand side of the dialog box, click on Options >>

In Connection Properties, Click Connect to database and then <Browse server ..>. Choose a DB that is in your availability group.

Then click on Additional Connection Parameters and type in ApplicationIntent=ReadOnly

Click connect and run SELECT @@SERVERNAMEand you should expect to see the instance name of your secondary replica, providing you have set up the read only routing correctly.

If you change connection and remove ApplicationIntent=ReadOnly from the Additional Connection Parameters, you should see the result as the name of your primary instance.

Summary

Hopefully these 2 simple techniques to test read intent connections to an AG Listener will be useful and help save you time. It’s a simple blog post but I wanted to write it because I was looking at the problem in too much depth and missing the obvious mistake of choosing my database context.

Where the extended events eventfile is located

5th April 2019 By John McCormack Leave a Comment

Do you need to find out where the extended events eventfile is located? Simply run the query below and use the WHERE clause if you know the name of the XE session.

[sql]

SELECT
s.name,
CAST(st.target_data AS XML).value(‘(/EventFileTarget/File/@name)[1]’,’nvarchar(256)’) AS target_data_file,
CAST(st.target_data AS XML) AS target_data_xml
FROM sys.dm_xe_session_targets st
JOIN sys.dm_xe_sessions s
ON st.event_session_address = s.[address]
WHERE s.name = ‘Custom XE Session Name’ — Optional if you know the name

[/sql]

More info about the DMVs

Put tempdb files on D drive in Azure IAAS

21st March 2019 By John McCormack 5 Comments

Tempdb files on D drive you say?

Azure warn you not to to store data on the D drive in Azure VMs, but following this advice could mean you are missing out on some very fast local storage. It’s good general advice because this local storage is not permanently attached to your instance, meaning you could lose data or log files if your VM is stopped and restarted but what if you could afford to lose certain files? Say files that are recreated during startup anyway.

TempDB is the ideal candidate for this. No other database is suitable! Putting the tempdb data and log files onto D drive can be achieved quite easily with a little bit of effort. And you will most likely see a big improvement in tempdb read/write latency.

Just look at these results! Even for someone like me who sometimes looks at charts and often can’t see the obvious, I don’t think there is any denying when the change took place here.

tempdb latency azure IAAS — Blazing fast now

Overview of how to configure SQL Server to use D drive for tempdb on Azure VM

Run the ALTER DATABASE command for all of the files you need to change e.g.
- ALTER DATABASE [tempdb] MODIFY FILE ( NAME = N'tempdev', FILENAME = 'D:\TempDB\tempdev.mdf')
Create Folder D:\TempDB or something similar
Restart SQL Server and make sure your files are created in D: as expected
Manually remove any old tempdb files still lying around

Now to make sure tempdb is created when the VM restarts

Create a Powershell script which will create the D:\TempDB folder on startup and start the SQL services
- You could use this script at https://community.idera.com/database-tools/blog/b/community_blog/posts/configuring-tempdb-on-azure-iaas-for-sql-server
- Schedule this script with a Task Scheduler startup job
- Change your execution policy to remote signed if it isn’t that. Set-ExecutionPolicy RemoteSigned
Change the startup type of your SQL Services to Automatic (Delayed Start)
Test this thoroughly in dev before you rely on it in production. If it doesn’t work, you’ll need to remember how you configured tempdb and manually create the folders, then start SQL Server. Not a fun task under pressure.

More tempdb goodness

Configuring TempDB for SQL Server 2016 instances

Glasgow SQL User Group Presentation – SQL Server on AWS

14th March 2019 By John McCormack Leave a Comment

You can run SQL Server on AWS?

Tonight, I presented my SQL Server on AWS talk to the Glasgow SQL User Group. This blog post was prepared in advance so I’ll add some observations on how I found the experience once I get a chance.

I’ve attached some important links from the talk which provide more detail on the subjects covered.

Links to my AWS content

AWS documentation

For slides or examples, please contact me directly and I’ll share them.