Author Archives: nakulvachhrajani

About nakulvachhrajani

Nakul Vachhrajani is a SQL Server MCTS, TOGAF certified Technical Architect with Capgemini having a total IT experience of more than 12 years. Nakul is an active blogger, and has been a guest columnist for SQLAuthority.com and SQLServerCentral.com. Nakul presented a webcast on the “Underappreciated Features of Microsoft SQL Server” at the Microsoft Virtual Tech Days Exclusive Webcast series (May 02-06, 2011) on May 06, 2011. He is also the author of a research paper on Database upgrade methodologies, which was published in a CSI journal, published nationwide. In addition to his passion about SQL Server, Nakul also contributes to the academia out of personal interest. He visits various colleges and universities as an external faculty to judge project activities being carried out by the students. Disclaimer: The opinions expressed herein are his own personal opinions and do not represent his employer’s view in anyway.

#0418 – SQL Server – How to disable Shared Memory connections and configure a SQL Server instance to accept connections only via TCP/IP?


As part of my normal development activities, I use my trusted developer instance on my local machine. However, one of the main things I realized was that while I could connect to the instance using SQL Server Management Studio (SSMS), I could not connect to my instance via some of my SSIS packages.

I realized shortly afterwards that this was because the instance only has “Shared Memory” enabled as the protocol for connections by default. I turned on TCP/IP as well and was able to complete my work. However, I thought it best to document the steps I took for future reference.

What is my current connection using – Shared Memory or TCP/IP?

Before we go any further, let us investigate the default connection mechanism used by client applications running on the same machine as the SQL Server instance.

To do this, I have opened connections to the SQL Server via both – SSMS and SQLCmd and am then querying the DMV (sys.dm_exec_connections) to investigate the protocol being used for the connection. Session Ids used by each connection have been highlighted in the image below.

A connection to my local SQL Server instance via SQL Server Management Studio
Another connection using SQLCMD to the same SQL Server instance

Now, because my connections are active, I can take their session Ids and query the DMV – sys.dm_exec_connections which will give me the physical transport protocol that is used by this connection.

As can be clearly seen, the physical transport protocol used when connecting to a SQL Server on the same machine is “Shared Memory” by default.

If I explicitly try to connect to the instance using TCP/IP, note that I get an error #26 (Error Locating Server/Instance Specified):

Error 26 (Error Locating Server/Instance Specified) when connecting to the SQL server using TCP/IP network protocol in the SSMS “Connection Properties” window

Enabling TCP/IP

In order to change the connection, one needs to use the SQL Server Configuration Manager.

In the Configuration Manager, when we navigate to the SQL Server Network Configuration -> Protocols for <SQL Server Instance>, we notice that TCP/IP and Named Pipes are disabled – only the Shared Memory protocol is enabled.

Notice that by default, only the “Shared Memory” physical transport protocol is enabled

Now, all that needs to be done is to enable TCP/IP from the Protocol properties (right-click -> Enable or simply double-click to open the properties window) and restart the SQL Server service.

TCP/IP connections are now enabled.

Specifying Transport Protocol when connecting to the database

Now that I have reconfigured the SQL Server instance, I can now specify the protocol when connecting to a SQL server:

  1. In SSMS, when connecting to a SQL Server, click on “Options”
  2. Under “Connection Properties”, choose “TCP/IP” as the connection protocol
Accessing the “Connection Properties” screen when connecting to an instance using the Management Studio
Choosing the Network Protocol as “TCP/IP”

When I use the DMV (sys.dm_exec_connections) to check the session, I can see that it is now using TCP/IP and not Shared Memory.

Connections to the SQL Server are now using TCP/IP as the physical network protocol

How to disable Shared Memory?

One of the questions that we started with was how to disable “Shared Memory” for connections?

This can be achieved in the same way as we enabled TCP/IP. Simply use the SQL Server Configuration Manager to disable the “Shared Memory” protocol.

Disabling the Shared Memory protocol

I hope you will find this post helpful.

Disclaimer: Please DO NOT try this on your production SQL Server instances.

References:

Until we meet next time,

Be courteous. Drive responsibly.

#0417 – SQL Server – Select row count of local temp tables


I was recently contacted by a fellow team member who was interested in finding out the number of records in a temporary table which was being used as part of a long-running script.

As I had mentioned in one of my previous posts, local temporary tables are only accessible to the connection that created them. Hence, if a script is already running, the only connection that can execute queries against the local temporary table is the connection itself making this requirement a tricky one to work with.

The Solution

The solution for this is to realize that all tables – permanent or local consume storage either in a system/user database or in the tempdb. Hence, we can access this meta-data to fulfill our requirement. Let’s check it out with a demo.

Demo

In any window, we can access the dynamic management view (DMV): [sys].[dm_db_partition_stats]. As we know, this DMV returns page and row-count information for every partition in the current database.

So, let’s open a new query window in the SQL Server Management Studio and run the following query:

--Create a new test database
IF (DB_ID('SQLTwins') IS NULL)
BEGIN
    CREATE DATABASE [SQLTwins];
END
GO

USE [SQLTwins];
GO

--Window 01
BEGIN
    IF OBJECT_ID('tempdb..#SQLTwinsDemo','U') IS NOT NULL
    BEGIN
        DROP TABLE [dbo].[#SQLTwinsDemo];
    END

    CREATE TABLE [dbo].[#SQLTwinsDemo] ([Number] INT         NOT NULL,
                                        [Value]  VARCHAR(50) NOT NULL
                                       );

    INSERT INTO [dbo].[#SQLTwinsDemo] ([Number],
                                       [Value]
                                      )
    VALUES (9, 'Nine' ),
           (8, 'Eight'),
           (7, 'Seven'),
           (6, 'Six'  ),
           (5, 'Five' ),
           (4, 'Four' ),
           (3, 'Three'),
           (2, 'Two'  ),
           (1, 'One'  );
END

Now, in another window, try to run a simple row count query. As expected, it would return an error.

USE [SQLTwins];
GO
SELECT COUNT(*) FROM [dbo].[#SQLTwinsDemo];
GO
Msg 208, Level 16, State 0, Line 3
Invalid object name '#SQLTwinsDemo'.

Now, let’s use the DMV: [sys].[dm_db_partition_stats] in another window to get the row count information.

USE [SQLTwins];
GO
--Now, do this in Window #2
BEGIN
    SELECT [st].[name] AS [TableName],
           [partitionStatistics].[row_count] AS [RowCount]
    FROM [tempdb].[sys].[dm_db_partition_stats] AS [partitionStatistics]
    INNER JOIN [tempdb].[sys].[tables] AS [st] ON [st].[object_id] = [partitionStatistics].[object_id]
    WHERE [st].[name] LIKE '%SQLTwinsDemo%'
      AND ([partitionStatistics].[index_id] = 0  --Table is a heap
           OR
           [partitionStatistics].[index_id] = 1  --Table has a clustered index
          )
END
Fetching RowCount for local temporary tables using SQL Server DMVs

Hope it helps!

Until we meet next time,

Be courteous. Drive responsibly,

#0416 – SQL Server – Msg 8101 – Use column lists when working with IDENTITY columns


I have often written about IDENTITY columns on my blog. Identity columns, most commonly used to implement auto-increment keys, have been around for more than a decade now. Yet, I often see teams run into interesting use cases especially in cases where data is being migrated from one system to another.

Today’s post is based on one such incident that came to my attention.

The team was trying to migrate data from one table to another as part of an exercise to change the database structure for more efficiency. When moving the data from one table to another, they were using the option (SET IDENTITY_INSERT ON) in order to explicitly insert values into the Identity column. However, they were running into an error.

Msg 8101, Level 16, State 1, Line 24
An explicit value for the identity column in table 'dbo.tIdentity' can only be specified when a column list is used and IDENTITY_INSERT is ON.

Here is a simulation of what they were doing:

USE tempdb;
GO
SET NOCOUNT ON;
--Prepare the environment
--   Create a table, and add some test data into it
--Safety Check
IF OBJECT_ID('tIdentity','U') IS NOT NULL
    DROP TABLE dbo.tIdentity;
GO
--Create a table
CREATE TABLE dbo.tIdentity (IdentityId INT IDENTITY(1,1),
                            IdentityValue VARCHAR(10)
                           );
GO
--Turn Explicit IDENTITY_INSERT ON and insert duplicate IDENTITY values
SET IDENTITY_INSERT dbo.tIdentity ON;
GO
--NOTICE: No column list has been supplied in the INSERT
INSERT INTO dbo.tIdentity
VALUES (1, 'One'),
       (2, 'Two');
GO

--RESULTS
--Msg 8101, Level 16, State 1, Line 24
--An explicit value for the identity column in table 'dbo.tIdentity' can only be pecified when a column list is used and IDENTITY_INSERT is ON.

The Solution

Let’s re-read the error. It clearly gives an indication of what the issue is – if we need to insert an explicit value into Identity columns, we need to explicitly use column lists in our insert statements, as shown below.

USE tempdb;
GO
SET NOCOUNT ON;
--Prepare the environment
--Create a table, and add some test data into it
--Safety Check
IF OBJECT_ID('tIdentity','U') IS NOT NULL
    DROP TABLE dbo.tIdentity;
GO

--Create a table
CREATE TABLE dbo.tIdentity (IdentityId INT IDENTITY(1,1),
                            IdentityValue VARCHAR(10)
                           );
GO

--Turn Explicit IDENTITY_INSERT ON and insert duplicate IDENTITY values
SET IDENTITY_INSERT dbo.tIdentity ON;
GO

--NOTE: Column list has been supplied in the INSERT,
--      so, no errors will be encountered    
INSERT INTO dbo.tIdentity ([IdentityId], [IdentityValue])
VALUES (1, 'One'),
       (2, 'Two');
GO

--Confirm that data has been inserted
SELECT IdentityId,
       IdentityValue
FROM dbo.tIdentity;
GO

--Now that data has been inserted, turn OFF IDENTITY_INSERT
SET IDENTITY_INSERT dbo.tIdentity OFF;
GO

-----------------------------------------------------------------
--RESULTS
----------
--IdentityId  IdentityValue
--1           One
--2           Two
 -----------------------------------------------------------------

Hope you will find this helpful.

Untill we meet next time,

Be courteous. Drive responsibly.

#0415 – SQL Server – Performance Tuning – Use STRING_AGG to generate comma separated strings


With more and more data being exchanged over APIs, generating comma-separated strings are becoming a much more common requirement.

A few years ago, I wrote about two different ways to generate comma-separated strings. The most common one I find to be in use when generating comma-separated values from a table is the intermediate conversion of XML. This however, is a very costly mechanism and can potentially take minutes for the query to run depending upon the amount of data involved.

SQL Server 2017 brings a new aggregate function that can be used to generate comma-separated values extremely fast. The function is STRING_AGG().

Here’s a sample of it’s usage:


 --WARNING: THIS SCRIPT IS PROVIDED AS-IS AND WITHOUT
-- WARRANTY.
-- FOR DEMONSTRATION PURPOSES ONLY
--Step 01: Generate Temp table to store source data
DECLARE @NamesTable TABLE ([Id] INT,
[Name] NVARCHAR(50)
);
--Step 02: Generate test data
INSERT INTO @NamesTable
VALUES (1, 'A'),
(2, 'D'),
(2, 'C'),
(3, 'E'),
(3, 'H'),
(3, 'G');
--Step 03: Using STRING_AGG to generate comma-separated strings
SELECT STRING_AGG(tbl.Name, ',') AS [CommaSeparatedString]
FROM @NamesTable AS tbl;
GO
/RESULTS**
CommaSeparatedString
A,D,C,E,H,G
*/

Advantages of STRING_AGG:

  • Can be used just like any other aggregate function in a query
  • Can work with any user supplied separator – doesn’t necessarily have to be a comma
  • No manual step required – Separators are not added at the end of the concatenated string
  • STRING_AGG() is significantly faster than using XML based methods
  • Can be used with any compatibility level as long as the version is SQL Server 2017 (or higher) and Azure SQL database

Here’s an example of how STRING_AGG can be used with any separator:

 --WARNING: THIS SCRIPT IS PROVIDED AS-IS AND WITHOUT
-- WARRANTY.
-- FOR DEMONSTRATION PURPOSES ONLY
--Step 01: Generate Temp table to store source data
DECLARE @NamesTable TABLE ([Id] INT,
[Name] NVARCHAR(50)
);
--Step 02: Generate test data
INSERT INTO @NamesTable
VALUES (1, 'A'),
(2, 'D'),
(2, 'C'),
(3, 'E'),
(3, 'H'),
(3, 'G');
--Step 03: Using STRING_AGG to generate comma-separated strings
SELECT STRING_AGG(tbl.Name, '-*-') AS [CustomSeparatorString]
FROM @NamesTable AS tbl;
GO
/RESULTS**
CustomSeparatorString
A--D--C--E--H--G /

A minor challenge

As with every new feature, there may be a small usability challenge with STRING_AGG. One cannot use keywords like DISTINCT to ensure that only distinct values are used for generating the comma-separated string. There is however a Azure feedback item open where you can exercise your vote if you feel this feature is useful.

Further Reading

  • Different ways to generate a comma-separated string from a table [Blog Link]
  • STRING_AGG() Aggregate Function [MSDN BOL]

Until we meet next time,

Be courteous. Drive responsibly.

Import Event Viewer Logs into Excel

#0414 – Analyzing Event Viewer Logs in Excel


When troubleshooting issues, the Event Viewer is one of the most handy of all tools. Assuming that appropriate coding practices were used during application development, the Event Viewer contains a log of most problems – in the system, in the configuration or in the application code.

The only problem is analyzing the Event Viewer logs when you have a thousand events. It becomes extremely difficult to try and answer questions like the following while going through events serially:

  1. Events logged by type for each source
  2. Events by severity
  3. Events by category
  4. And many more such analytical questions…

These analytical requirements are best achieved with tools like Microsoft Excel. And so, I went about analyzing Event Viewer logs in Microsoft Excel in just 2 steps.

Step #1: Export the Event Viewer Logs to XML

  1. Once the Event Viewer is launched, navigate to the Event Log to be evaluated
  2. Right-click on the Event Log and choose “Save All Events As” option
  3. In the Save As dialog, choose to save the Events as an XML file
    • If asked to save display information, you can choose not to store any or choose a language of your choice

And that’s it – it completes the 1st step!

Screenshot showing how to Save the Event Viewer Logs
Save the Event Viewer Logs
Screenshot showing how to save the Event Viewer Logs as an XML file
Choose to save the Event Viewer Logs as an XML file

Step #2: Import the XML file into Excel

  1. Launch Microsoft Excel
  2. In the File -> Open dialog, choose to search files of “XML” type
  3. Select the exported Event Viewer Log file
  4. In the Import Options, you can choose to import as an “XML Table”
    • Excel will prompt to create/determine the XML schema automatically. It’s okay to allow Excel to do so

And that’s it – the Event Viewer Logs are now in Excel and you can use all native Excel capabilities (sort, filter, pivot and so on).

Choose to import the Event Viewer Logs into Excel as an XML table
Import the Event Viewer Logs as an XML table
Image showing the successfully imported Event Viewer data into Microsoft Excel
Event Viewer Logs successfully imported into Excel

I do hope you found this tip helpful. If you have more such thoughts and ideas, drop in a line in the Comments section below.

Until we meet next time,

Be courteous. Drive responsibly.