02Jul 2012 by Grant Fritchey 12 Comments

Querying Information from the Plan Cache, Simplified

SQL Server, T-SQL
One of the great things about the Dynamic Management Objects (DMOs) that expose the information in plan cache is that, by their very nature, they can be queried. The plans exposed are in XML format, so you can run XQuery against them to pull out interesting information. For example, what if you wanted to see all the plans in cache that had a Timeout as the reason for early termination from the optimizer? It’d be great way to see which of your plans were less than reliable. You could so like this: WITH XMLNAMESPACES(DEFAULT N'http://schemas.microsoft.com/sqlserver/2004/07/showplan'), QueryPlans AS ( SELECT RelOp.pln.value(N'@StatementOptmEarlyAbortReason', N'varchar(50)') AS TerminationReason, RelOp.pln.value(N'@StatementOptmLevel', N'varchar(50)') AS OptimizationLevel, --dest.text, SUBSTRING(dest.text, (deqs.statement_start_offset / 2) + 1, (deqs.statement_end_offset - deqs.statement_start_offset) / 2 + 1) AS StatementText, deqp.query_plan, deqp.dbid, deqs.execution_count, deqs.total_elapsed_time, deqs.total_logical_reads, deqs.total_logical_writes FROM…
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25May 2011 by Grant Fritchey 26 Comments

Oh ****!

SQL Server
Did you ever accidentally close SQL Server Management Studio? And, in closing SSMS, did you get the prompt that says “Save changes to the following items?” And did you, completely unthinkingly, with a query you had just been working on, hit Cancel? Yeah, me neither. What kind of idiot does that…. OK. I confess. I just did that. Silly thing it was, but I had just spent at least 1/2 an hour working on a query and now it was gone…. or was it? I had just run the query and had been looking at the results when I closed SSMS. Initially, I panicked and started thinking about how I could get the data back (somewhere there’s a file I’ve heard). Then it occurred to me, I had just been…
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23May 2011 by Grant Fritchey 6 Comments

SQL Azure Query Tuning

Azure
SQL Azure is still SQL Server at the end of the day. This means it is entirely possible to write queries against SQL Azure that really… what’s a good word… stink. So what do you do? It’s all in the cloud. You couldn’t possibly tune the queries, right? Wrong. Many of the same tools that you have available to you, such as execution plans and dynamic management objects, are still available in SQL Azure. Let’s talk DMOs for a second. First off, don’t make the mistake I did of trying to run these outside the context of a specific database on SQL Azure. You’ll get extremely inconsistent results, trust me on this. Anyway, I did a quick run-down on some of the most used DMOs for performance tuning, the sys.dm_exec_*…
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05Jan 2011 by Grant Fritchey 4 Comments

Encryption and the Performance DMOs

T-SQL
Ever wonder what you can see in the performance oriented DMOs when stored procedures were encrypted? Me neither. But, I did get that question during my DMO presentation at the PASS Summit. I did not have an answer. I did get an answer from Johan Bijnens (twitter) from the audience, which I repeated without entirely knowing what I was saying. I decided that I ought to actually know the answer to that question, so here’s a little experiment. I'm going to create a simple stored procedure: CREATE PROCEDURE dbo.GetSalesDetails (@SalesOrderId INT) AS SELECT soh.AccountNumber, sod.LineTotal FROM Sales.SalesOrderHeader AS soh JOIN Sales.SalesOrderDetail AS sod ON soh.SalesOrderID = sod.SalesOrderID WHERE soh.SalesOrderID = @SalesOrderID When I create this procedure and run it, you can see the general performance of the query being run…
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21Oct 2009 by Grant Fritchey 1 Comment

Characters

SQL Server, T-SQL, Tools
No, I'm not talking about a Dickens novel. I'm talking about the number of characters in a string. I had a painful time recently because of the word "characters."  If you take a look at the dynamic management view sys.dm_exec_sql_text you can get the queries that have been run on your system that are still in the cache. It's a great utility. Better still, you can get specific statements from the code that are actively running through sys.dm_exec_requests or ones that have run through sys.dm_exec_query_stats. To do this is very simple. Each of these DMV's has a pair of columns, statement_start_offset and statement_end_offset. These columns, and I'm quoting directly from books online measure the "number of character" offset from the beginning of the SQL string and from the end of…
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12Feb 2009 by Grant Fritchey 11 Comments

Missing Index Information and Query Stats

SQL Server, T-SQL
So the goal was to find a way to pull information from sys.dm_exec_query_stats so that we could identify poor performing procedures that were in cache at the moment and combine it with missing index information from sys.dm_db_missing_index_details. We're combining these because we're working with a Microsoft Dynamics CRM database that is almost all ad hoc queries and lots of them are against tables with missing indexes. The hope was to identify necessary indexes merely by looking at the longest running queries. Unfortunately there is no way to combine data from the missing indexes set of DMV's and all the execution DMV's that show query stats, execution plan, etc. None of the missing index tables has a plan handle or a plan hash column that would allow you to combine that…
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18Dec 2008 by Grant Fritchey No Comments

2008 Index Fragmentation

Uncategorized
I forgot all about this, but a script I wrote on using all the new functionality of dynamic management views & functions to do index defragmentation and rebuilds got published over at SQL Server Central. It could stand a bit of tweaking, but gets the job done on several of the systems I've tested it on so far.
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03Dec 2008 by Grant Fritchey 3 Comments

Dynamic Management Views Put to Work on Blocking

SQL Server, T-SQL
This is my first pass at a modern (2005/2008) blocking monitoring script. I think it's a decent blocking script to capture information about blocks as they are occurring. Filters can be applied and it wouldn't be hard at all to add on other information such as execution plans, plan hash, etc. SELECT  tl.request_session_id AS WaitingSessionID        ,wt.blocking_session_id AS BlockingSessionID        ,wt.resource_description        ,wt.wait_type        ,wt.wait_duration_ms        ,DB_NAME(tl.resource_database_id) AS DatabaseName        ,tl.resource_associated_entity_id AS WaitingAssociatedEntity        ,tl.resource_type AS WaitingResourceType        ,tl.request_type AS WaitingRequestType        ,wrt.[text] AS WaitingTSql        ,btl.request_type BlockingRequestType        ,brt.[text] AS BlockingTsql FROM    sys.dm_tran_locks tl         JOIN sys.dm_os_waiting_tasks wt         ON tl.lock_owner_address = wt.resource_address         JOIN sys.dm_exec_requests wr         ON wr.session_id = tl.request_session_id         CROSS APPLY sys.dm_exec_sql_text(wr.sql_handle) AS wrt         LEFT JOIN sys.dm_exec_requests br         ON br.session_id = wt.blocking_session_id         OUTER APPLY…
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02Dec 2008 by Grant Fritchey 6 Comments

More Dynamic Management Views: sys.dm_tran_locks

SQL Server, T-SQL
I'm working on the chapter on blocking in the new book. Explaining blocking of course means explaining locks. Prior to 2005, to understand locks, you went to sp_lock. Not anymore. Now you can query sys.dm_tran_locks. It's so much more sophisticated than the old system procedure.  Best of all, the information within it is simply a view into the internal locking infrastructure, so you're not placing extra load or extra processing on the system to marshal this data. A simple query to get basic locking information would look like this:   SELECT tl.request_session_id             ,tl.resource_database_id             ,tl.resource_associated_entity_id             ,tl.resource_type             ,tl.resource_description             ,tl.request_mode             ,tl.request_status   FROM sys.dm_tran_locks tl That just outputs roughly the same information as sp_lock. Lots more detail, not available in sp_lock, is available if you need it. Things…
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