Thursday 21 July 2016

The 'SkipErrors' parameter for the Replication Distribution Agent

Having seen many errors in SQL Server Replication, I can say that the vast majority of them are reported at replication agents level like Distribution Agent, Log Reader Agent, Snapshot Agent, Queue Reader Agent, and so on. Unfortunately, some of  them are mostly related to Primary and Foreign Key conflicts, and to solve them either one by one or by reconfiguring the replication we may need much time, therefore, we need to look for an option to allow the operation to continue while we work to fix them as soon as possible. Luckily, this option is the 'SkipErrors' parameter which I have used many times to deal with them. Likewise, you can use it for skipping other errors. 
Today's post will show how to use the' SkipErrors' parameter which allows to skip specific errors so that the data synchronization process is not stopped. This parameter is configurable in the profile of the Distribution Agent and has as input the error number we may want to skip.
The following picture shows an error (with code 547 related to an Foreign Key issue) in the Distribution Agent process and we see how the transactions are being queued due to this error, consequently, there is a need to fix it so as to allow the rest of pending transactions are moved on. (Distribution Agent reads sequentially the table 'msrepl_commands' to get the command to execute in the subscribers, this means that First in the Queue is the First Out to be moved to subscribers.)

Other common errors where you can use 'SkipErrors' parameter is when there are not some rows in the subscriber to apply the changes (The row was not found at the Subscriber when applying the replicated command). The error code for this case is 20598.

I mentioned before that the 'SkipErrors' parameter is configurable inside the Distribution Agent profile and that is what we are going to do right now. Firstly, we need to create a customized profile based on the Default profile and write in the 'Value' column the numbers of the errors (to be skipped)  separated by colons as we can see in the following picture 20598:547.

Having done that, we may have to restart the Distribution Agent. Next time the Distribution Agent starts up, it will load the new customized profile with the error codes to be skipped (ignored). Finally, not only will we verify that many errors are skipped, but also the Distribution Agent is running with no problem.

Just to finish writing this post, keep in mind that the transactions with these errors were missed, which means that you will not be able to recover them and may affect your data consistency. In other words, we must use 'SkipErrors' parameter with extreme caution. Let me know any remark you may have. Thanks for reading.

Wednesday 20 July 2016

How to query the windows users that access via windows groups from SQL Server

At times while monitoring a database server, we may need to know not only which SQL users are accessing, but also windows users for security and auditing purposes. Frankly, this task may be quite simple to get it completed when all of those users are created and visible inside the database engine. Despite this, it is not a surprise that windows users can access via windows groups which means that DBAs can not see them from SQL Server easily unless we have the manner to list them. Luckily, there is an extended stored procedure named “xp_logininfo” that we need to use to get that information. (The 'xp_logininfo' asks the Active Directory for the windows users.)
First of all, this system stored procedure takes two input parameters. The first one is the windows group name, and the second one is the value ‘members’.  For instance, it lists the windows users that access via the windows group ' MyDomain\SQLProdUsrs'. (You need to have “sysadmin” role to execute it.)
EXEC xp_logininfo  @acctname ='MyDomain\SQLPrdUsrs',  @option='members' 
Naturally, this is perfect if we only have one windows group to query. As time goes by, we are likely to get created more windows groups inside the database engine and in no time we will need to create an specific script to figure out the other windows users. Here is that code.

CREATE TABLE #WindowGroup(

    server_name varchar(100),

    account_name varchar(300),

    type char(8),

    privilege char(9) ,

    mapped_login_name varchar(300) ,

    permission_pathsysname  varchar(300)



DECLARE @WindowGroupName varchar(max)

DECLARE @db [NCHAR](128)  

DECLARE cursor_WG CURSOR FOR SELECT [name] FROM sys.server_principals WHERE TYPE='G' 


OPEN cursor_WG

    FETCH NEXT FROM  cursor_WG INTO @WindowGroupName



            INSERT #WindowGroup(account_name , type , privilege  ,mapped_login_name  ,permission_pathsysname   )

            EXEC xp_logininfo  @acctname =@WindowGroupName  ,  @option =  'members' 

        FETCH NEXT FROM cursor_WG INTO @WindowGroupName


CLOSE cursor_WG



UPDATE #WindowGroup SET server_name=@@servername

select server_name AS ServerName, account_name as WindowsAccountName, Type, Privilege, mapped_login_name as MappedLoginName, permission_pathsysname as WindowsGroupName

FROM #WindowGroup 

ORDER BY permission_pathsysname,mapped_login_name

DROP TABLE #WindowGroup



As you have seen, the T-SQL code is simply easy to understand. Clearly, it filters the windows groups by indicating the value ‘G’ for the Type column of the system view “sys.server_principals”, and eventually through the cursor each of them is read. Now I hope you make the most out of this script to have better visibility of the windows users accessing the databases. Thanks for reading again!

Saturday 16 July 2016

SQL Mirroring Port could stop working unexpectedly

When it comes to diagnosing and fixing some SQL Mirroring issues we may have to face with bizarre causes that could stop working a database mirroring and as a result the state of it will be "disconnected". For instance, one of the most common problems is that the SQL mirroring port may stop working unexpectedly. Consequently, the whole database mirroring functionality will stop working too. We basically configure SQL Server mirroring to use the port 5022 by default which works good enough for the vast majority of cases. To be perfectly honest, there is not an urgent need to change it since the issue is not about the port number (or mirroring configuration) but the port itself.

While working on fixing the issue, we may think the database mirroring port may have stopped working or blocked for some security reason which we do not know accurately at the beginning of the situation. Nevertheless, the reason should be investigated further by the Network team so as to prevent from getting the same issue in the future again. Having clear the situation, I am going to show one way to have the database mirroring working again. To begin with, we need to figure out what is the current number port of the mirroring being used.

We can see that the mirroring port is 5022, so we can opt to change it.


Only after successfully completing that will we have to restart the database engine. Finally, we need to restore the original port and then restart again the database engine.


Having done it, we will see the database mirroring working properly. That's is all for now. I hope this tip also works for you. Let me know any remarks you may have. Thanks for reading.
HELLO, I'M PERCY REYES! — a book lover, healthy lifestyle lover... I've been working as a senior SQL Server Database Administrator (DBA) for over 20 years; I'm a three-time awarded Microsoft Data Platform MVP. I'm currently doing a PhD in Computer Science (cryptography) at Loughborough University, England — working on cryptographic Boolean functions, algorithmic cryptanalysis, number theory, and other algebraic aspects of cryptography. READ MORE