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Archive for June, 2015

SQL Server – Capture Execution Plan of a Currently Running Query/Process SPID

Posted in Performance, Queries, T-SQL, tagged , , , on June 4, 2015| 4 Comments »

DBAs most often face scenarios where they need to capture graphical execution plan of a query currently running on a live production instance because of multiple reasons like:

  • why a particular SPID is causing blocking
  • why is my query running slow
  • why isn’t the index getting used
  • which operator is costing more and why

While there are multiple ways to retrieve the execution plan, below is the query I always keep handy as I can run this safely on a live production server with minimal effort.

SELECT CONVERT(XML, c.query_plan) AS ExecutionPlan
FROM sys.dm_exec_requests a with (nolock)
OUTER APPLY sys.dm_exec_sql_text(a.sql_handle) b
OUTER APPLY sys.dm_exec_text_query_plan (a.plan_handle, a.statement_start_offset, a.statement_end_offset) c
LEFT JOIN sys.dm_exec_query_memory_grants m (nolock)
ON m.session_id = a.session_id
AND m.request_id = a.request_id
JOIN sys.databases d
ON d.database_id = a.database_id
WHERE  a.session_id = @@SPID --replace @@SPID with the SPID number for which you want to capture query plan
ORDER BY a.Start_Time

Hope this will be a good addition to your query bank.

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SQL Server – How to Calculate Length and Size of any field in a SQL Table

Posted in LOB, Performance, Queries, T-SQL, tagged , , , , , on June 4, 2015| 7 Comments »

Recently I came across a situation where queries are loading extremely slow from a table. After careful analysis we found the root cause being, a column with ntext datatype was getting inserted with huge amounts of text content/data. In our case DATALENGTH T-SQL function came real handy to know the actual size of the data in this column.

According to books online, DATALENGTH (expression) returns the length of the expression in bytes (or) the number of bytes SQL needed to store the expression which can be of any data type. From my experience this comes very handy to calculate length and size especially for LOB data type columns (varchar, varbinary, text, image, nvarchar, and ntext) as they can store variable length data. So, unlike LEN function which only returns the number of characters, the DATALENGTH function returns the actual bytes needed for the expression.

Here is a small example:

Use AdventureWorksLT2012
GO
Select ProductID, DATALENGTH(Name) AS SizeInBytes, LEN(Name) AS NumberOfCharacters
FROM [SalesLT].[Product]

–Results

DATALENGTH

If your column/expression size is too large like in my case, you can replace DATALENGTH(Name) with DATALENGTH(Name)/1024 to convert to KB or with DATALENGTH(Name)/1048576 to get the size in MB.

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