Tuesday 7 June 2016

How to Calculate Binary Bit Masks


Ok, so I know this post is a bit geeky, but there is nothing wrong with a little geeky fun from time to time.

SQL Server uses bit maps for various thinks, such as CPU affinity and Server Agent Operator's pager availability, but how do you work with bit maps? Well, it is a case of calculating the integer expresentation of the bit map value. This is made more complex because the INT data type is a 32-bit signed integer, meaning that some of the representations will be negative numbers.

Using CPU affinity as an example, the table below shows the processor number, bit mask and signed integer representation for processors 0 - 31.

Processor Number Bit Mask                                                               Signed Integer Representation
0                             0000 0000 0000 0000 0000 0000 0000 0001      1
1                             0000 0000 0000 0000 0000 0000 0000 0010      2
2                             0000 0000 0000 0000 0000 0000 0000 0100      4
3                             0000 0000 0000 0000 0000 0000 0000 1000      8
4                             0000 0000 0000 0000 0000 0000 0001 0000     16
5                             0000 0000 0000 0000 0000 0000 0010 0000     32
6                             0000 0000 0000 0000 0000 0000 0100 0000     64
7                             0000 0000 0000 0000 0000 0000 1000 0000     128
8                             0000 0000 0000 0000 0000 0001 0000 0000     256
9                             0000 0000 0000 0000 0000 0010 0000 0000     512
10                           0000 0000 0000 0000 0000 0100 0000 0000     1024
11                           0000 0000 0000 0000 0000 1000 0000 0000     2028
12                           0000 0000 0000 0000 0001 0000 0000 0000     4096
13                           0000 0000 0000 0000 0010 0000 0000 0000     8192
14                           0000 0000 0000 0000 0100 0000 0000 0000     16384
15                           0000 0000 0000 0000 1000 0000 0000 0000     32768
16                           0000 0000 0000 0001 0000 0000 0000 0000     65536
17                           0000 0000 0000 0010 0000 0000 0000 0000     131072
18                           0000 0000 0000 0100 0000 0000 0000 0000     262144
19                           0000 0000 0000 1000 0000 0000 0000 0000     524288
20                           0000 0000 0001 0000 0000 0000 0000 0000     1048576
21                           0000 0000 0010 0000 0000 0000 0000 0000     2097152
22                           0000 0000 0100 0000 0000 0000 0000 0000     4194304
23                           0000 0000 1000 0000 0000 0000 0000 0000     8388608
24                           0000 0001 0000 0000 0000 0000 0000 0000     16777216
25                           0000 0010 0000 0000 0000 0000 0000 0000     33554432
26                           0000 0100 0000 0000 0000 0000 0000 0000     67108864
27                           0000 1000 0000 0000 0000 0000 0000 0000     134217728
28                           0001 0000 0000 0000 0000 0000 0000 0000     268435456
29                           0010 0000 0000 0000 0000 0000 0000 0000     536870912
30                           0100 0000 0000 0000 0000 0000 0000 0000     1073741824
31                           1000 0000 0000 0000 0000 0000 0000 0000     -2147483648

On a 32-core server, there are 2.631308369336935e+35 possible combinations for processor affinity, but a few examples are included below.

Aligned Processors Bit Mask Signed                                                  Integer Representation
0 and 1                    0000 0000 0000 0000 0000 0000 0000 0011      3
0, 1, 2, and 3           0000 0000 0000 0000 0000 0000 0000 1111      15
8 and 9                    0000 0000 0000 0000 0000 0011 0000 0000      768
8, 9, 10, and 11       0000 0000 0000 0000 0000 1111 0000 0000      3840
30 and 31                1100 0000 0000 0000 0000 0000 0000 0000      -1073741824
28, 29, 30, and 31   1111 0000 0000 0000 0000 0000 0000 0000      -268435456

Because an integer has a a maximum range of 2^32 then the Affinity Mask can only accommodate values for up to 32 CPUs. If your server has between 33 and 64 processors, then SQL Server relies on a 2nd value, called the 64 Bit Affinity Mask, to store the details of the next 32 CPUs.

There are a number of calculators available online, for calculating the signed integer representation of a bit mask. I tend to use www.binaryconvert.com/convert_signed_int.html

SQL Enterprise Edition vs SQL Enterprise Core Based Licensing Edition


There is a common point of confusion, when DBAs decide what version of SQL Server to install. Until SQL Server 2012, if you needed Enterprise Edition, then things were straight forward. When SQL Server 2012 was released, however, things changed, with the release of core-based licensing.

Subsequently, SQL Server Enterprise Edition should not be installed in most cases. It is designed as a "tide-me-over" edition, to see companies through, as they move from CAL based, to core based licenses.

What a lot of people do not realize, is there is actually a technical difference between the two editions. The two products have different SKUs and SQL Server Enterprise Edition will only support a maximum of 20 cores.

If you have a server large enough to test this out, you can see for yourself, by running the following query:

SELECT COUNT(*) FROM sys.dm_os_schedulers WHERE status = 'VISIBLE ONLINE'

If you are using Enterprise Edition, then the maximum value returned will be either 20, or 40 if the server has hyper-threading turned on.

Check out my books on Apress.com:

Pro SQL Server Administration

SQL Server AlwaysOn Revealed

Expert Scripting and Automation for SQL Server DBAs 

Use SQL 2016 Query Store to Remove Ad-hoc Plans


Ad-hoc query plans consume memory and can be of limited use. It is a good idea to remove ad-doc query plans if they are not being recused. The query below demonstrates how to use Query Store metadata to identify and remove unwanted ad-hoc query plans from the cache. 

DECLARE @SQL NVARCHAR(MAX)

SELECT @SQL =
(
        SELECT 'EXEC sp_query_store_remove_query ' 
                + CAST(qsq.query_id AS NVARCHAR(6)) + ';' AS [data()]
        FROM sys.query_store_query_text AS qsqt
        JOIN sys.query_store_query AS qsq
               ON qsq.query_text_id = qsqt.query_text_id
        JOIN sys.query_store_plan AS qsp
               ON qsp.query_id = qsq.query_id
        JOIN sys.query_store_runtime_stats AS qsrs
               ON qsrs.plan_id = qsp.plan_id
        GROUP BY qsq.query_id
        HAVING SUM(qsrs.count_executions) = 1
               AND MAX(qsrs.last_execution_time) < DATEADD (HH, -24, GETUTCDATE())
        ORDER BY qsq.query_id
        FOR XML PATH('')
) ;

EXEC(@SQL) ;

You can find out more about the Query Store in SQL Server 2016, in my new book, Expert Scripting and Automation for SQL Server DBAs, available from Apress at www.apress.com/9781484219423?gtmf=s or at Amazon at www.amazon.com/Expert-Scripting-Automation-Server-DBAs/dp/1484219422?ie=UTF8&keywords=expert%20scripting%20and%20automation&qid=1465300485&ref_=sr_1_1&sr=8-1

Navigating a SQL Server Instance with PowerShell


As well as navigating a folder structure with commands such as get-childitem, and set-location, PowerShell can also be used to navigate the SQL Server object hierarchy of an instance. You can connect PowerShell to the SQL Server database engine provider by using set-location to navigate to SQLSERVER:\SQL The information returned by get-childitem is dependent on the current location of the object hierarchy. The table below shows what information is returned from each level of the hierarchy.

Location
Information Returned
SQLSERVER:\SQL
The name of the local machine
SQLSERVER:\SQL\ComputerName  
The names of the database engine instances installed on the local machine
SQLSERVER:\SQL\ComputerName\InstanceName
Instance level object types
Lower levels
Object types or objects contained within the current location

Once you have navigated to the level of the hierarchy, in which you are interested, you are able to use PowerShell to perform basic operations against objects at that level. For example, the script below will navigate to the "tables" namespace within the AdventureWorks2016 database and rename the dbo.DatabaseLog table, to dbo.DatabaseLogPSThe dir commands will display the original name and new name of the table.


sl SQLSERVER:\SQL\ESASSMgmt1\MASTERSERVER\DATABASES\ADVENTUREWORKS2016\TABLES

dir | where{$_.name -like "*DatabaseLog*"}

rename-item -LiteralPath dbo.DatabaseLog -NewName DatabaseLogPS

dir | where{$_.name -like "*DatabaseLog*"}

More complex tasks that do not have a specific cmdlet, associated with them can be performed by using the invoke-sqlcmd cmdlet. 

You can also start PowerShell from within SSMS. This is done by selecting "Start PowerShell" from the context menu of an object folder, within Object Explorer. This will cause the PowerShell CLI to be invoked, with the initial location being set to the object folder that you used to invoke the CLI.

My new book, Expert Scripting and Automation for SQL Server DBAs contains extensive details and examples of how to use PowerShell to administer SQL Server. The book is available from Apress at www.apress.com/9781484219423?gtmf=s or from Amazon, at www.amazon.com/Expert-Scripting-Automation-Server-DBAs/dp/1484219422?ie=UTF8&keywords=expert%20scripting%20and%20automation&qid=1465300485&ref_=sr_1_1&sr=8-1

Monday 6 June 2016

Running Administrative Queries Across Multiple Servers

As a DBA, sometimes we are asked questions, such as "What is total size of databases used by Application A?" or "Does Application A have any databases with a mismatched collation?"

If Application A has a single database server, then these questions are straight forward to answer. If Application A has databases dispersed across multiple instances, however, then the question becomes more time consuming to answer. The temptation is to connect to each instance individually, and copy/pasting the query.

It is possible to make use of Central Management Servers, to simplify answering this kind of question, however. For example, if you are supporting a large, dispersed data-tier application, you can create a server group, containing each of the instances that support the application.

For example, in the image below, you can see that I have created two folders; one for the EMEA region and another for the US.


We can now register our servers\instances under the relevant group. Below, you can see that I use the New Server Registration dialog box, to add servers. In this example, I will add two servers, nammed ESPROD1 and ESPROD2, to the  Production | NTAM server group. 


Imagine a scenario where you have a number of SQL Server instances, where the database files are hosted on a SAN (Storage Area Network). You come into work one morning, to find that there has been an issue with the production SAN and you need to check all databases, on all instances, for corruption. This can be easily achieved, using central management servers.
Because you have a separate SAN for each environment, in each data center, you will only want to check the servers in the NTAM server group, as this is where the SAN issue occurred. Therefore, select New Query, from the context menu of the NTAM server group. This will cause a new query window to be displayed and we will use DBCC CHECKDB to check the consistency of all databases on both instances. This is demonstrated below:

EXEC sp_MSforeachDB 'DBCC CHECKDB (?)' ;

This command executes the undocumented sp_MSForeachDB system stored procedure. We pass the command that we want to run against each database, into this procedure and use ? as a placeholder for the database name. This is automatically populated by sp_MSForeachDB, for each database in turn.

Below is a partial output. You can easily see which results relate to each server, along with the execution context. You may also notice the query status bar is pink instead of yellow and displays the name of the server group that we can the command against.


To learn much more about Central Management Servers, including further examples of useful queries to run across instances, full details of how to configure them and a demonstration of how to evaluate Policies against Central Management Servers or Server Groups, please refer to my new book, "Expert Scripting and Automation for SQL Server DBAs"


Expert Scripting and Automation for SQL Server DBAs

My new book "Expert Scripting and Automation for SQL Server DBAs" is now available to pre-order on Amazon and Apress.com




The link for Apress.com is www.apress.com/9781484219423?gtmf=s

It is worth noting that the expected release date on Amazon is not correct. Publication is actually expected in August.