SQL Server 2008 R2 : Query Analysis - SSMS Client Statistics, Using the SET SHOWPLAN Options

Tip

Unlike the graphical execution plans, SSMS does not provide a way to save the client statistics. Fortunately, the statistics are displayed using a standard grid control. You can right-click the client statistics and choose Select All. Then you right-click and select Copy. You can then paste the information into a spreadsheet program such as Excel, which allows you to save the information or perform further statistical analysis on it.

2. Using the SET SHOWPLAN Options

In addition to the graphical execution plans available in SSMS, SQL Server 2008 provides three SET SHOWPLAN options to display the execution plan information in a text or XML format. These options are SET SHOWPLAN_TEXT, SET SHOWPLAN_ALL, and SET SHOWPLAN_XML. When one of these options is enabled, SQL Server returns the execution plan generated for the query, but no results are returned because the query is not executed. It’s similar to the Display Estimated Execution Plan option in SSMS.

You can turn on the textual execution plan output in a couple of ways. One way is to issue the SET SHOWPLAN_TEXT ON, SET SHOWPLAN_ALL ON, or SET SHOWPLAN_XML ON command directly in the SSMS query window. These commands must be executed in a separate batch by themselves before running a query.

SHOWPLAN_TEXT

Typing the following command in an SSMS query window turns on the SHOWPLAN_TEXT option:

SET SHOWPLAN_TEXT ON
GO

Setting this option causes the textual showplan output to be displayed in the results panel but does not execute the query. You can also enable the SHOWPLAN_TEXT option by choosing the Query Options item from the Query menu. In the Query Options dialog, you click the Advanced item and check the SET SHOWPLAN_TEXT option.

The SHOWPLAN_TEXT option displays a textual representation of the execution plan. Listing 1 shows an example for a simple inner join query.

Listing 1. An Example of SHOWPLAN_TEXT Output

set showplan_text on
go
select st.stor_name, ord_date, qty
from stores st join sales_noclust s on st.stor_id = s.stor_id
where st.stor_id between 'B100' and 'B199'
go
StmtText
-------------------------------------------------------------------------------
select st.stor_name, ord_date, qty
from stores st join sales_noclust s on st.stor_id = s.stor_id
where st.stor_id between 'B100' and 'B199'

(1 row(s) affected)

StmtText
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
-------------------------
  |--Nested Loops(Inner Join, OUTER REFERENCES:([Bmk1002], [Expr1006]) WITH
 UNORDERED PREFETCH)
       |--Nested Loops(Inner Join, OUTER REFERENCES:([st].[stor_id]))
       |   |--Clustered Index
Seek(OBJECT:([bigpubs2008].[dbo].[stores].[UPK_storeid]
 AS [st]), SEEK:([st].[stor_id] >= 'B100' AND [st].[stor_id] <= 'B199')
 ORDERED FORWARD)
       |   |--Index Seek(OBJECT:([bigpubs2008].[dbo].[sales_noclust].[idx1] AS
 [s]), SEEK:([s].[stor_id]=[bigpubs2008].[dbo].[stores].[stor_id] as
 [st].[stor_id]),  WHERE:([bigpubs2008].[dbo].[sales_noclust].[stor_id] as
 [s].[stor_id]>='B100' AND [bigpubs
       |--RID Lookup(OBJECT:([bigpubs2008].[dbo].[sales_noclust] AS [s]),
 SEEK:([Bmk1002]=[Bmk1002]) LOOKUP ORDERED FORWARD)

(5 row(s) affected)


					  

The output is read from right to left, similarly to the graphical execution plan. Each line represents a physical/logical operator. The text displayed matches the logical and physical operator names displayed in the graphical execution plan. If you can read the graphical query plan, you should have no trouble reading the SHOWPLAN_TEXT output.

In the example in Listing 1, SQL Server performs a clustered index seek on the stores table, using the UPK_storeid index, and a nonclustered index seek on sales_noclust, using index idx1. The inputs are combined using a nested loop join. Finally, a RID lookup is performed to retrieve the ord_date and qty information from the sales_noclust table.

When the SHOWPLAN_TEXT option is set to ON, execution plan information about all subsequent SQL Server 2008 statements is returned until the option is set to OFF. Also, all subsequent commands are optimized but not executed. To turn off the textual showplan output and allow execution of commands again, type the following command:

SET SHOWPLAN_TEXT OFF
GO

SHOWPLAN_ALL

The SHOWPLAN_ALL option displays the same textual execution plan information as the SHOWPLAN_TEXT option, and it also provides additional columns of output for each row of textual showplan output. These columns provide much of the same information available in the graphical execution ToolTips. Table 1 describes the information provided in the data columns returned by the SHOWPLAN_ALL option.

SHOWPLAN_XML

When SET SHOWPLAN_XML is set to ON, SQL Server does not execute the query but returns execution information for each T-SQL batch as an XML document. The execution plan information for each T-SQL batch is contained in a single XML document. Each XML document contains the text of the statements in the batch, followed by the details of the execution steps and operators. The document includes the estimated costs, numbers of rows, indexes used, join order, and types of operators performed.

The SHOWPLAN_XML option generates the same XML output as the Show Estimated Execution Plan option in SSMS. In essence, you are looking at the same information, just without the pretty pictures. As a matter of fact, you can save the output from the SHOWPLAN_XML option to a file and open it back into SSMS as a SQL plan file. The recommended approach is to configure the query window to return results to a grid. If you return the results as text or to a file, the maximum output size for a character column in SSMS is 8,192 bytes. If the XML document exceeds this length, it is truncated and does not load correctly. In the grid results, the maximum size of XML data is 2MB.

After you run the query and generate the grid results, you can right-click on the result row and choose the Save Results As option to specify the file to save the results to. If all goes well, you end up with a .sqlplan file that you can then load back into SSMS for further analysis at a later date.