New per-operator level performance stats included in SQL2016 SP1 and SQL2014 SP2

Traditionally, we were used to getting only basic runtime performance stats per operator regarding to CPU, I/O and Memory, which were not good enough to allow us to automate recollecting tasks of them. I strongly believe that DBAs are always overwhelmingly interested in diagnosing some issues proactively so as to prevent bad-written queries from using hardware resources inefficiently. Luckily, this convoluted situation has been changed radically in SQL Server 2016 and SQL Server 2014 SP2 since Microsoft has included very useful information per operator (and also per thread in the scope of each operator) which can be seen looking into the Showplan XML. For instance, we are going to see that information for the following query (in this case it has run under a serial plan, that is one thread).



This is its actual execution plan.


It is highlighted all what is new in SQL2016, SQL2016 SP1 and SQL2014 SP2. Therefore, we can appreciate CPU and I/O runtime performance stats for the Clustered Index Scan operator on 'PurchaseOrderDetail' table such as I/O reads, CPU time and Elapsed time. In a parallel plan you will be able to see information per thread in each operator.



And now we will see not only CPU and I/O performance stats for the Hash operator but also Memory performance stats.



All this information can also be seen in the Properties window in the context of each operator inside the Actual Execution Plan by using the latest version of SSMS. If you display the detail of each statistic, the detail per thread will be seen when working with parallel execution plan.



Having seen this, not only are we now able to look into useful performance stats by using Showplan XML and SSMS, but also we can create some scripts for administration and optimization purposes in order to pick up queries with poor performance and then optimise them. That is all for now. Let me know any remark you may have. Thanks for reading.

How to create new Logins and Users for an AlwaysOn Availability Group

(This tip also applies for Log Shipping and Database Mirroring)

Surely, after setting up an AlwaysOn Availability Group (AG) we are going to need to create additional Logins and Users who must have access and the same permissions across the replica servers so that users can work on each server properly. At times it may end up being a confusing task as SQL Logins may not have matched to the correct SQL Users and therefore users will only access to the SQL instance but not databases in the Secondary Replicas. Do not forget that we cannot create Users directly in Secondary Replicas as they are only read-only, read intent or no access.

To begin with, we need to understand some basic concepts. Logins and Users in SQL Server are different things. Logins allow to access only to the SQL instance and perform tasks at that level such as create/alter/drop databases, alter configurations of the SQL instance, etc. whereas Users allow to get into the databases and work inside them doing delete/update/insert data, create/alter/drop tables, stored procedures, triggers, etc. So, traditionally we always need to have a Login and a User matched each other so as to have access to databases.(Since SQL Server 2012 it is possible to create SQL User without a SQL Login but this aspect is not covered in this post.)

In this context, when it comes to creating new Logins and Users not only will we need to create them in the Primary Replica, but also we have to make sure they also are created in each Secondary Replica so that Users and Applications can log on successfully with the same permissions as they have in the Primary Replica. So we might get some big issues if they are not matched correctly.

Obviously, we need to create the new Login at Primary Replica level and then give the permissions inside the databases. Consequently, ONLY the user will be replicated immediately to each Secondary Replica. So, because the Login is NOT a database object it will not be replicated (it is a server object), which means that we need to create the Login in each Secondary Replica server manually. If the Login is a Windows Login then all what we need to do is to create that Windows Login in each Secondary Replica. A Windows login only has a SID across the whole domain so it will be automatically matched to its Windows User with the same name in each database in the Secondary Replica server. We do not need to know its SID before creating it.

USE [master]
GO
CREATE LOGIN [DOMAIN\percy.reyes] FROM WINDOWS WITH DEFAULT_DATABASE=[master]
GO

Now when it comes to working with SQL Logins and SQL Users we must figure out and take the correct SID of the SQL Login in order to use it to create the same SQL Login in each Secondary Replica server. Therefore, we can query the SID of the SQL Login we need by executing the following code like this.

Having got it, we can use it to create the SQL Login by indicating the correct SID. (Do not forget to use the same password and other properties too.)

USE [master]
GO
CREATE LOGIN [preyes] WITH  PASSWORD=N'P4s$Word&1', SID= 0x8AA780458D0F9E4F95D4204B8E022C83, CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF
GO

In conclusion, only after successfully following this technique will the SQL Login match automatically to the correct user inside the database. It also means that the user will be able to log on any Secondary Replica server with the right permissions inside the databases. That is all for now. Let me know any remarks you may have. Thanks for reading.

How to monitor database file space usage in SQL Server

Undoubtedly, when it comes to monitoring database file space usage we need a simple way to do it. Fortunately, SQL Server has considerable quantity of DMV and System Functions to allows us to get closely related information about it. Today's post has the intention of providing a practical way of warning us in case the free database file space is less than the threshold of 20%. With this alert in mind, we will be able to make a preventive decision in order to prevent the performance of in-flight transactions from being impacted.

I am coming up with a simple query to achieve that. Firstly, we need to create a physical temporary table 'FileSpace' which will hold related information for each database. Having successfully creating the table, the following step is to execute the adequate logic, in the context of each database user via 'sp_msforeachdb', to collect file space usage which will be reported in the end. I am getting space usage information of each database file by using FILEPROPERTY system function.

The execution of the entire script (including creation of the table) may be automated via a SQL Job in order to send yourself an alert with format HTML by using database mail. Unluckily, this code does not include the logic to send that email but it is not something difficult to complete, therefore, just do it. That is all for now. Let me know any remarks you may have. Thanks for reading.

Here is the whole script.

USE [master]
GO
CREATE TABLE [dbo].[FileSpace](
    [DatabaseName] [nvarchar](128) NULL,
    [FileName] [sysname] NOT NULL,
    Type varchar(10) not null,
    [FileSizeGB] [decimal](10, 2) NULL,
    [SpaceUsedGB] [decimal](10, 1) NULL,
    [SpaceFreeGB] [decimal](10, 1) NULL,
    [SpaceFree%] [decimal](10, 1) NULL,
    Physical_Name varchar(max)
) ON [PRIMARY]
GO
 
EXEC sp_MSforeachdb '
USE [?]
insert into master.DBO.[FileSpace]([DatabaseName] ,    [FileName] , Type,    [FileSizeGB],    [SpaceUsedGB] ,    [SpaceFreeGB] ,    [SpaceFree%],Physical_Name )
select db_name() DatabaseName, name FileName, Type_Desc ,
cast(size/128.0/1024.0 as decimal(10,2)) SizeGB, 
cast(FILEPROPERTY(name,''SpaceUsed'') /128.0/1024.0  as decimal(10,1)) SpaceUsedGB, 
cast((size - FILEPROPERTY(name,''SpaceUsed'') ) /128.0/1024.0 as decimal(10,1)) SpaceFreeGB, 
cast(((size - FILEPROPERTY(name,''SpaceUsed'') )/(size*1.0)) *100 as decimal(10,1)) [SpaceFree%], physical_name
FROM sys.database_files'

SELECT * FROM FileSpace
WHERE [SpaceFree%]<=20
DROP TABLE FileSpace

Creating alerts for monitoring proactively SQL Server AlwaysOn Availability Groups

When it comes to monitoring databases we have to do it proactively by using alerts implemented natively or via T-SQL code inside SQL Jobs running recurrently (I know we do have the AlwaysOn Dashboard, but personally I do not have time to check it all the time). As a result of this situation, so rapidly do we have databases working on production environment that we may need to have alerts working as well. In this post I am going to show how to have the most important AlwaysOn Availability Group alerts implemented. To begin with, I would basically suggest creating alerts only for these error messages.



Undoubtedly, we may need more alerts. Therefore, we will need to look into ‘sys.messages’ system object and look for error messages closely related to AlwaysOn Availability Group feature. Only after identifying them will we be able to create particular alerts taking the ‘message_id’ number.  To illustrate, I will query ‘sys.messages’ by using keywords like ‘Availability’, ‘suspended’, ‘failed’, ‘disconnected’, etc.

SELECT * FROM sys.messages  
WHERE (  [text] LIKE '%Availability%Disconnected%' OR   [text] LIKE '%Availability%not%synchroni%'
OR   [text] LIKE  '%Availability%suspended%'    OR   [text] LIKE '%Availability%failed%' OR   [text] LIKE '%Availability%chang%role%'
OR   [text] LIKE '%Availability%resumed%' )  AND language_id=1033

As you have seen, they are about 63 messages (depending on the SQL Server version you are working on). I do believe that these messages are the be-all and end-all so we might not need to implement additional alerts. Put differently, they are enough. Nevertheless, we might filter out some messages we do not consider important and include others to monitor AlwaysOn Failover Cluster instead.

SELECT * FROM sys.messages  
WHERE (  [text] LIKE '%Availabiliy%replica%' OR   [text] LIKE '%Database%replica%' OR   [text] LIKE '%primary%role%'
    OR   [text] LIKE '%secondry%role%' OR   [text] LIKE '%availability%group%' OR   [text] LIKE '%WSFC%'
    OR   [text] LIKE '%primary%replica%' OR   [text] LIKE '%secondary%replica%' OR   [text] LIKE '%alwayson%')
    AND    [text] NOT LIKE '%No user action is required.%'
    AND severity<>10
    AND language_id=1033

After having got the error number, the next step is to create the alert for the error by using ‘sp_add_alert’ system stored procedure which accepts basic parameters like the name for the alert and ‘message_id’ (taken from ‘sys.messages’). The rest of parameters will be the same for each alert. So, you can create the other alerts by replacing the name and ‘message_id’, for instance, the following example is based on the error number 41418. (We also create the notification to send an email to us when the alert is raised. Obviously, not until having successfully configured SQL Agent service to use Database Mail will you be able to receive the email.)

USE [msdb]
GO
EXEC msdb.dbo.sp_add_alert @name=N'41418 HADR Alert', 
        @message_id=41418, 
        @severity=0, 
        @enabled=1, 
        @delay_between_responses=0, 
        @include_event_description_in=1, 
        @notification_message=N'Contact your Database Administrator urgently.', 
        @job_id=N'00000000-0000-0000-0000-000000000000'
GO
EXEC msdb.dbo.sp_add_notification @alert_name=N'41418 HADR Alert', @operator_name=N'DBA', @notification_method = 1

To try out to see whether or not the alert is working, we will need to raise the error manually via RAISERROR command with ‘LOG’ parameter (to see the message logged in the SQL Server error log).

RAISERROR(41418,16,1) WITH LOG;

Having done that, we can see the following message in error log:

Likewise, you will get the email.

To sum up, I am convinced that these sorts of alert will always work for monitoring Availability Groups and others. You just need to spend some time on figuring out about the error messages and then go ahead and create the right alert for you. I hope you enjoy this post and let me know any remark you may have. Thanks for reading again.

Using ‘sp_browsereplcmds’ to diagnose SQL Server Replication issues

While diagnosing SQL Server transactional replications issues, we may need to look into some pending commands inside the Distribution database. In other words, not only do we have to monitor pending commands, but also take some actions so as to keep working the replication. For instance, at times we may have to kill some specific commands because of errors which do not allow other commands to be moved to subscribers. Before doing that, we firstly need to identify which commands have to be removed from the queue by using ‘sp_browsereplcmds’ system stored procedure. This basically accepts many input parameters like article_id:

EXEC SP_BROWSEREPLCMDS @article_id = 1

After executing it, we are going to filter only the pending commands for the Article in question. (Remember that an article in replication is directly related to a table. You can query ‘sysarticles’ system table inside the published database.)


Another parameter we can use in order to get more specific information is the transaction sequence number which is essentially the identifier for the transaction. Luckily, when reading some errors, we can see the sequence number and command ID which allow us to identify exactly the root cause we need to work on with ease.

EXEC SP_BROWSEREPLCMDS @xact_seqno_start = '0x00000027000000B50008',@xact_seqno_end = '0x00000027000000B50008' 

There are other parameters like command ID to get only the command we need to look into, and also the database ID to get all commands for that database.

EXEC SP_BROWSEREPLCMDS @xact_seqno_start = '0x00000027000000B50008',@xact_seqno_end = '0x00000027000000B50008' ,
@publisher_database_id = 33, @article_id = 1,@command_id= 1

Be cautious, do not execute ‘sp_browsereplcmds’ without any parameter on production database environments as they can have millions of commands inside Distribution database and as a result of this we will not get what we need rapidly and at the same time we will affect the database server performance. I hope you can find this post interesting when it comes to troubleshooting replication issues. Let me know any remark you may have. Thanks for reading.