Nearly anytime you see the command DBCC FREEPROCCACHE mentioned in a blog post, magazine article or book, you get some sort of a scary warning about how you should not use it on a production system, or else life as we know it will end. For example, Books Online says this:

Use DBCC FREEPROCCACHE to clear the plan cache carefully. Freeing the plan cache causes, for example, a stored procedure to be recompiled instead of reused from the cache. This can cause a sudden, temporary decrease in query performance. For each cleared cachestore in the plan cache, the SQL Server error log will contain the following informational message: "SQL Server has encountered %d occurrence(s) of cachestore flush for the ‘%s’ cachestore (part of plan cache) due to ‘DBCC FREEPROCCACHE’ or ‘DBCC FREESYSTEMCACHE’ operations." This message is logged every five minutes as long as the cache is flushed within that time interval.

I would argue that running DBCC FREEPROCCACHE does not cause that much distress, even on a very busy OLTP system. It will cause a pretty minor CPU spike for a few seconds on most systems as the plans get recompiled. It can actually be pretty useful for resetting the cached_time time for sys.dm_exec_procedure_stats so that it is the same for most of the stored procedures in your normal workload. That makes it easier to pick out your most expensive queries or stored procedures on a cumulative basis when you are looking at things like total worker time or total logical reads.

Having said all that, I want to show a few methods for clearing all or part of the procedure cache that are somewhat less impactful on the system. Running DBCC FREEPROCCACHE is kind of a brute force approach, so if you are concerned about that, you can run one of the variations shown below:

-- Example 1 (Sledgehammer)
-- Remove all elements from the plan cache for the entire instance
DBCC FREEPROCCACHE;

-- Flush the cache and suppress the regular completion message
-- "DBCC execution completed. If DBCC printed error messages, contact your system administrator."
DBCC FREEPROCCACHE WITH NO_INFOMSGS;

-- Example 2 (Ballpeen hammer)
-- Remove all elements from the plan cache for one database
-- Get DBID from one database name first
DECLARE @intDBID INT;
SET @intDBID = (SELECT [dbid]
                FROM master.dbo.sysdatabases
                WHERE name = 'AdventureWorks');

-- Flush the procedure cache for one database only
DBCC FLUSHPROCINDB (@intDBID);

-- Example 3 (Scalpel)
-- Remove one plan from the cache
-- Get the plan handle for a cached plan
SELECT cp.plan_handle, st.[text]
FROM sys.dm_exec_cached_plans AS cp
CROSS APPLY sys.dm_exec_sql_text(plan_handle) AS st
WHERE [text] LIKE N'%/* GetOnlineSearchResultsMonday %';

-- Remove the specific plan from the cache using the plan handle
DBCC FREEPROCCACHE (0x05000800F7BA926C40C15055070000000000000000000000);

Note: Cross posted from Rob Pellicaan IS Blog.

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- A checklist for writing fast queries
- Sargability of queries
- A checklist for creating indexes
- A legend of the ‘Execution Plan Icons’, including some optimizing tips and tricks.
- All datatypes, including memory-usage and indication for best performing types
- All string functions
- All system functions
- All date and time functions
- A list of all dateparts
- The cursor functions
- The mathematical functions

Source: http://www.dotnet4all.com/snippets/2008/04/factsheet-for-sql-server-developers.html

Direct link: http://www.dotnet4all.com/snippets/factsheet%20SQL%20Server.pdf

Note: Cross posted from Rob Pellicaan IS Blog.

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This is the proof:

While I have been recording my installations steps, I will not put them here, as I came across another post that describes the required steps in even more detail, including the solution to my broken setup.

A big thanks to Vidalis for posting the required installation steps:

http://powerpivot-info.com/post/66-step-by-step-guide-on-installing-powerpivot-for-sharepoint

Everything is public Beta material, so you can give it a go yourself!

I downloaded and installed Sun VirtualBox : I use this to host the 64-bit guest on my Windows 7 laptop. Alternatives are Windows Server 2008 with Hyper-V or VMware.

Note: Cross posted from Rob Pellicaan IS Blog.

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The book –written for charity – contains content from 53 MVPs with Paul Nielsen, Kalen Delaney, Greg Low, Adam Machanic, Paul S. Randal and Kimberly L. Tripp as editors. When purchased through Manning a larger amount of the proceeds go to WarChild.

More info: http://www.sqlskills.com/BLOGS/KIMBERLY/post/SQL-Server-MVP-Deep-Dives-(book-for-charity).aspx.

Note: Cross posted from Rob Pellicaan IS Blog.

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I find it very useful not for problem reporting, but for documenting installation steps, because it will follow you in every step you take, with screenshots and comments. No more copy and pasting individual screenshots and documenting them!

A little demo and some more details: http://www.istartedsomething.com/20090111/windows-7-problem-steps-recorder-miracle-tool/

Note: Cross posted from Rob Pellicaan IS Blog.

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If you have a medium to large database in SQL Server, with lots of stored procedures, functions or views, it can sometimes be difficult to keep track of whether you have used certain options (such as RECOMPILE).  The queries below show some different things you can discover by querying sys.sql_modules and sys.objects.

-- List all modules in the current database
    SELECT OBJECT_NAME(sm.[object_id]) AS [object_name], o.[type],
           o.type_desc, sm.[definition]
    FROM sys.sql_modules AS sm
    INNER JOIN sys.objects AS o
    ON sm.[object_id] = o.[object_id]
    ORDER BY o.[type];

    -- Look for modules that use a specific term (Method 1)
    SELECT OBJECT_NAME(sm.[object_id]) AS [Object Name], sm.[definition]
    FROM sys.sql_modules AS sm
    WHERE sm.[definition] LIKE '%SQLCONTENT01%';

    -- Look for modules that use a specific term (Method 2)
    SELECT OBJECT_NAME(id) AS [Object Name], [text]
    FROM sys.syscomments
    WHERE [text] LIKE '%SQLCONTENT01%'

    -- Find stored procedures that have WITH RECOMPILE set
    SELECT OBJECT_NAME(sm.[object_id]) AS [Object Name],
           sm.[definition], sm.is_recompiled
    FROM sys.sql_modules AS sm
    INNER JOIN sys.objects AS o
    ON sm.[object_id] = o.[object_id]
    WHERE sm.is_recompiled = 1
    AND o.type_desc = 'SQL_STORED_PROCEDURE';

Note: Cross posted from Rob Pellicaan IS Blog.

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So I decided I would go for Sun’s VirtualBox and download and install the 180-day trail of Windows Server 2008 R2.

I want to try and see if extending the 180 expiration still works by disabling the timesync between the host and the vm, so only the time that the VM is actually on counts up to the 180 days (see Dealing with the Team System 2010 CTP expiration)

A way to disable the timesync was posted by Rick Guyer: VirtualBox: Disable time sync between host and client.

Some additional comments:

1) vboxmanage.exe is in C:\Program Files\Sun\VirtualBox on the host.

2) the VM has to be shutdown. It will not return a error when is running, but it won’t work.

3) You have to also disable the Internet Time sync within your guest OS.

Update!  WARNING: When you shutdown the VM and then start it again, it will resync the time once. So until I find a better solution, I have to make sure to never shutdown the VM, but use either “restart” or “save state”.

On the positive side: Man, this combination (VirtualBox + Windows 2008 R2) is fast! Boot-up time of the VM til the CTRL-ALT-DEL is only 20 seconds!

Note: Cross posted from Rob Pellicaan IS Blog.

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Thanks goes out to Aaron Bertrand for posting this trick on his blog:

http://sqlblog.com/blogs/aaron_bertrand/archive/2009/10/10/bad-habits-to-kick-using-select-omitting-the-column-list.aspx

Note: Cross posted from Rob Pellicaan IS Blog.

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Question: How much is $1/$345, rounded at 4 decimals?

Take a calculator and it will tell you: 0.0029.

Take Excel and it will tell you: 0.0029.

Take SQL Server and it will tell you: 0.0028.

Euh… wait a minute… did you say 0.0028? Isn’t that 3-4% off?

Seems SQL Server, when using the MONEY datatype, doesn’t round values, but truncates them instead. See the example below. I think it’s pretty shocking.

declare @m1 money, @m2 money, @r1 decimal(19,4)
declare @d1 decimal(19,4), @d2 decimal(19,4), @r2 decimal(19,4)
declare @f1 float, @f2 float, @r3 float;
set @m1 = 1.00;
set @m2 = 345.00;
set @r1 = @m1/@m2;
set @d1 = 1.00;
set @d2 = 345.00;
set @r2 = @d1/@d2;
set @f1 = 1.00;
set @f2 = 345.00;
set @r3 = @f1/@f2;
select @r1, @r2, @r3;

A interesting follow-up on one of the articles was made though by Adam Machanic that undermined one of our own best practices for a bit (which was to not use conversions or functions on the left side of a WHERE clause, because it prevents indexes from being used effectively). What Adam showed was that in SQL 2008, in conjunction with the addition of the DATE type, the query optimizer received a minor upgrade, which makes the following query use an Index Seek instead of a full Index Scan.

SELECT
    COUNT(*)
FROM #dates
WHERE
    CONVERT(DATE, the_date) = CONVERT(DATE, GETDATE());
GO

I am interested in how many more of these query optimizations have been implemented and will be implemented in the future.

Full details on his blog: http://sqlblog.com/blogs/adam_machanic/archive/2009/10/20/what-happened-today-date-and-date-ranges-over-datetime.aspx