INF: How to Profile Transact-SQL Code in Stored Procedures and Triggers

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SUMMARY

Profiling is used to tune code to make it more efficient or faster. Profiling is done by timing and counting the number of times a piece of code is executed, and recording the results so that the slow parts of the code can be identified. Then the code can be rewritten to be faster and more efficient. Profiling Transact-SQL code in SQL Server is sometimes difficult. However, profiling can provide the following information, which is sometimes necessary:
  • The number of times a stored procedure or trigger is run.
  • The amount of time (including maximum and minimum times) a stored procedure or trigger takes to run.
  • The amount of time (including maximum and minimum times) an individual command in a stored procedure or trigger takes to run.
To provide some profiling capabilities, SQL Server provides the SET STATISTICS TIME and SET STATISTICS IO commands, as well as the following columns in the system table: sysprocesses, cpu, physical_io and last_batch, However, using these options may require changes to applications to handle the new results. This article provides methods you can use so that the client applications do not need to change; the stored procedures and triggers that the application uses are changed instead.

MORE INFORMATION

This article defines some common methods to profile Transact-SQL code in SQL Server, if the following assumptions are true:
  • SQL Server is not compute-bound as defined in the following article in the Microsoft Knowledge Base:
    111405 : INF: SQL Server and Windows NT Thread Scheduling
  • All clients are processing rows efficiently and correctly, according to the following article in the Microsoft Knowledge Base:
    165951 : INF: Result Processing for SQL Server
Before proceeding, please note that profiling or debugging code does affect the amount of time the code takes to run.

The rest of this article is split into the following sections to make it more understandable:
  1. Simple Transact-SQL Time Profiling
  2. Simple Table-Based Stored Procedure and Trigger Profiling
  3. Advanced Table-Based Stored Procedure and Trigger Profiling
  4. Sample Stored Procedure to Manage Advanced Table-Based Profiling
  5. Additional Profiling Considerations

PART 1: Simple Transact-SQL Time Profiling

To perform a basic time performance test of a query such as "SELECT * FROM authors", you can wrap it in the following code:
   DECLARE @x datetime
   SELECT @x = GetDate()
   SELECT * FROM authors
   SELECT DateDiff(millisecond, @x, GetDate())
				

This method is very useful, but it does have some limitations. This method:
  • Requires that the client application handles the results set of the second SELECT statement.
  • Does not track the time over multiple runs of the query.
  • Does not work well in stored procedures and triggers.
To resolve these limitations, you can use a profile table to hold results so that the average run time, as well as the number of times it was run, can be computed. Part 2 discusses this method below.

PART 2: Simple Table-Based Stored Procedure and Trigger Profiling

The following is an example stored procedure that is used as a basis in both Parts 2 and 3 of this article to display these methods:
   CREATE PROCEDURE timeme AS
   SELECT * FROM pubs..authors
   RETURN
   GO
				

To perform time performance tests of a stored procedure or trigger, a table with the following definition is required:
   CREATE TABLE profile
   (id int primary key,
      trials int not null default 0,
      trltime int not null default 0)
   GO
				

The following code would be added to the stored procedure to record performance:
   /* Add this code at the beginning of the stored procedure. */ 
   DECLARE @x datetime
   SELECT @x = GetDate()

   /* Add this code at the end of the stored procedure. */ 
   UPDATE profile SET trials = trials + 1, trltime = trltime +
   DateDiff(MILLISECOND, @x, GetDate()) WHERE id = @@procid
				

The following is the modified stored procedure with the performance code added:
   CREATE PROCEDURE timeme AS
   DECLARE @x datetime
   SELECT @x = GetDate()
   SELECT * FROM pubs..authors
   UPDATE profile SET trials = trials + 1, trltime = trltime +
   DateDiff(MILLISECOND, @x, GetDate()) WHERE id = @@procid
   RETURN
   GO
				

Finally, the following is the execution of the stored procedure with the result of adding the stored procedure to the profile table as well as reporting the performance:
   INSERT profile (id) VALUES (Object_ID('timeme'))
   GO
   EXEC timeme
   GO
   SELECT Object_Name(id), trltime / trials FROM profile
   GO
				

This method is very useful but still has the limitation that profiling is not easily enabled and disabled. To resolve this limitation, the profile table needs to hold an enabled status, and the procedure needs to check if it should be profiled. Part 3 discusses this method below.

PART 3: Advanced Table-Based Stored Procedure and Trigger Profiling

The following is the updated profile table script for dynamic profiling:
   CREATE TABLE profile
   (id int primary key,
      enabled int not null default 0,
      trials int not null default 0,
      trltime int not null default 0)
   GO
				

The following is the updated stored procedure for dynamic profiling:
   CREATE PROCEDURE timeme AS
   DECLARE @debug int
   SELECT @debug = enabled FROM profile WHERE id = @@procid
   IF @debug = 1
   BEGIN
      DECLARE @ttime datetime
      SELECT @ttime = GetDate()
   END
   SELECT * FROM pubs..authors
   IF @debug = 1
      UPDATE profile SET trials = trials + 1, trltime = trltime +
      DateDiff(MILLISECOND, @ttime, GetDate())
      WHERE id = @@procid
   RETURN
   GO
				

Finally, the following is the execution of the stored procedure with the result of adding the stored procedure to the profile table as well as reporting the performance:
   INSERT profile (id) VALUES (Object_ID('timeme'))
   GO
   /* This run is not profiled because enabled is 1. */ 
   EXEC timeme
   GO
   UPDATE profile SET enabled = 1 WHERE id = Object_ID('timeme')
   GO
   EXEC timeme
   GO
   SELECT Object_Name(id), trltime / trials FROM profile
   GO
				

PART 4: Sample Stored Procedure to Manage Advanced Table-Based Profiling

   CREATE PROCEDURE resetprofile AS
   /* Disables and effectively resets profiling data for all objects. */ 
   DELETE profile
   RETURN
   GO
   CREATE PROCEDURE setupprofile @name char(30) = NULL AS
   /* Adds a stored procedure or trigger to profile table. */ 
   IF @name IS NULL
      PRINT 'usage: setupprofile <procedure or trigger name>'
   ELSE
      IF Object_ID(@name) IS NOT NULL
         INSERT profile(id) VALUES (Object_ID(@name))
      ELSE
         PRINT 'Invalid object name'
   RETURN
   GO
   CREATE PROCEDURE enableprofile @name char(30) = NULL as
   /* Enables one or more stored procedures or triggers in the profile
   table for profiling. */ 
   IF @name IS NULL
      UPDATE profile SET enabled = 1
   ELSE
      IF Object_ID(@name) IS NOT NULL
         UPDATE profile SET enabled = 1 WHERE id = Object_ID(@name)
      ELSE
         PRINT 'Invalid object name'
   RETURN
   GO
   CREATE PROCEDURE disableprofile @name char(30) = NULL AS
   /* Disables one or more stored procedures or triggers in the profile
   table for profiling. */ 
   IF @name IS NULL
      UPDATE profile SET enabled = 0
   ELSE
      IF Object_ID(@name) IS NOT NULL
         UPDATE profile SET enabled = 0 WHERE id = Object_ID(@name)
      ELSE
         PRINT 'Invalid object name'
   RETURN
   GO
   CREATE PROCEDURE reportprofile AS
   /* Reports performance of enabled stored procedures and triggers. */ 
   SELECT name = Object_Name(id),  'trial avg' = CASE WHEN trials <> 0 THEN
   trltime / trials ELSE 0 END, trials FROM profile WHERE enabled = 1
   RETURN
   GO
				

So you can change the run code of Part 3 above to the following:
   EXEC setupprofile 'timeme'
   GO
   /* This run is not profiled because enabled is 0. */ 
   EXEC timeme
   GO
   EXEC enableprofile 'timeme'
   GO
   EXEC timeme
   GO
   EXEC reportprofile
   GO
				

PART 5: Additional Profiling Considerations

When performing Transact-SQL profiling with a table for results as described above, consider the following:
  • Because object ids in SQL Server are not unique across databases, it is suggested for profiling in multiple databases to create the profiling table in each database to profile from the same database.
  • Creating the profile table so that there is only one row per page by padding the table with char(250) columns will prevent concurrency problems on the profile table. The following is an example of the padded profile table:
          CREATE TABLE profile
          (id int primary key,
             enabled int not null default 0,
             trials int not null default 0,
             trltime int not null default 0,
             fill1 char(250) not null default '',
             fill2 char(250) not null default '',
             fill3 char(250) not null default '',
             fill4 char(250) not null default '')
          GO
    
    						
  • To keep the profile table updates from altering performance as much as possible, lock the table into memory by using either the DBCC PINTABLE command or the sp_tableoption stored procedure with the pintable option. This has the added advantage that the profile table updates are not affected if the server is disk IO bound.


  • If a stored procedure or trigger that is being profiled is run in parallel by multiple clients, normal blocking may occur on the profile table.
  • If the stored procedures and triggers have multiple Return commands, each one needs to perform the profiling check and possibly update the profile table. If this is the case, the Goto command works well to simplify the profiling code. The following is an example of a stored procedure that has multiple Return commands:
          CREATE PROCEDURE timeme AS
          IF DB_Name() <> 'pubs'
             RETURN
          SELECT * FROM authors
          RETURN
          GO
    
    						
    The following is the stored procedure with profiling code also handling the Return commands:
          CREATE PROCEDURE timeme AS
          DECLARE @debug int
          SELECT @debug = enabled FROM profile WHERE id = @@procid
          IF @debug = 1
          BEGIN
             DECLARE @ttime datetime
             SELECT @ttime = GetDate()
          END
    
          IF DB_Name() <> 'pubs'
             --RETURN
             GOTO ENDME
    
          SELECT * FROM pubs..authors
    
          ENDME:
          IF @debug = 1
             UPDATE profile SET trials = trials + 1, trltime = trltime +
             DateDiff(MILLISECOND, @ttime, GetDate())
             WHERE id = @@procid
          RETURN
          GO
    
    						
  • The conditional check "IF @debug" should not noticeably alter performance, unless the profiled stored procedure or trigger does not perform any physical disk IO.
  • Profiling maximum and minimum trial timings can also be recorded by making the following changes:

    Change the profile table by adding four columns:
          CREATE TABLE profile
          (id int primary key,
             enabled int not null default 0,
             trials int not null default 0,
             trltime int not null default 0,
             tmin int not null default 1000000, -- minimum trial time
             tmax int not null default 0,      -- maximum trial time
             tmint int not null default 0,     -- trial number of minimum trial
             tmaxt int not null default 0,     -- trial number of maximum trial
             fill1 char(255) not null default '',
             fill2 char(255) not null default '',
             fill3 char(255) not null default '',
             fill4 char(255) not null default '')
          GO
    
    						
    The changes to the stored procedure are to get the minimum and maximum trial times when checking if it should be profiled. Also, one of three updates is run, based on if the current trial is the new minimum, new maximum, or just another trial.
          CREATE PROCEDURE timeme AS
          DECLARE @debug int
          DECLARE @min int
          DECLARE @max int
          SELECT @debug = enabled, @min = tmin, @max = tmax FROM profile WHERE
          id = @@procid
          IF @debug = 1
          BEGIN
             DECLARE @ttime datetime
             DECLARE @itime int
             SELECT @ttime = GetDate()
          END
    
          SELECT * FROM pubs..authors
    
          IF @debug = 1
          BEGIN
             SELECT @itime = DateDiff(MILLISECOND, @ttime, GetDate())
             SELECT @itime
             IF @min > @itime
                UPDATE profile SET trials = trials + 1, trltime = trltime +
                @itime, tmin = @itime, tmint = trials
                   WHERE id = @@procid
             ELSE
                IF  @max < @itime
                   UPDATE profile SET trials = trials + 1, trltime = trltime +
                   @itime, tmax = @itime, tmaxt = trials
                      WHERE id = @@procid
                ELSE
                   UPDATE profile SET trials = trials + 1, trltime = trltime +
                   @itime  WHERE id = @@procid
          END
          RETURN
          GO
    
    						
  • Profiling individual commands or sections of a stored procedure or trigger can also be recorded by making the following changes:

    The change to the profile table is to add a trial counter and a trial time column for each additional section or command that needs to be profiled.
          CREATE TABLE profile
          (id int primary key,
             enabled int not null default 0,
             trials int not null default 0,
             trltime int not null default 0,
             t1 int not null default 0,
             t1time int not null default 0,
             t2 int not null default 0,
             t2time int not null default 0,
             fill1 char(255) not null default '',
             fill2 char(255) not null default '',
             fill3 char(255) not null default '',
             fill4 char(255) not null default '')
          GO
    
    						
    The following is a sample stored procedure to use as a basis for this method:
          CREATE PROCEDURE timeme AS
          SELECT * FROM pubs..authors
          SELECT * FROM pubs..titleauthor
          SELECT * FROM pubs..titles
          RETURN
          GO
    
    						
    Assume that you want to know the total time for the procedure, the first two queries, and only the first query. The following stored procedure is modified to profile this information:
          CREATE PROCEDURE timeme AS
          DECLARE @debug int
          SELECT @debug = enabled FROM profile WHERE id = @@procid
          IF @debug = 1
          BEGIN
             DECLARE @ttime datetime
             DECLARE @t1time datetime
             DECLARE @t2time datetime
             DECLARE @t1 int
             DECLARE @t2 int
             SELECT @ttime = GetDate()
          END
    
          IF @debug = 1
          BEGIN
             SELECT @t1time = GetDate()
             SELECT @t2time = GetDate()
             SELECT * FROM pubs..authors
             SELECT @t1 = DateDiff(MILLISECOND, @t1time, GetDate())
          END
    
          SELECT * FROM pubs..titleauthor
          IF @debug = 1
             SELECT @t2 = DateDiff(MILLISECOND, @t2time, GetDate())
    
          SELECT * FROM pubs..titles
    
          IF @debug = 1
             UPDATE profile SET trials = trials + 1, trltime = trltime +
             DateDiff(MILLISECOND, @ttime, GetDate()), t1time = t1time + @t1,
             t1 = t1 + 1, t2time = t2time + @t2, t2 = t2 + 1
             WHERE id = @@procid
          RETURN
          GO
    
    						
    Note that this method can also profile performance of extended stored procedure calls as well as remote stored procedure calls.
For using SQL Server 7.0, the following modifications should be made
to the profiling table:
  • Do not use character fill columns to force one row per page.
  • Use Update Row Level Locking.

Properties

Article ID: 172117 - Last Review: October 16, 2003 - Revision: 3.0
APPLIES TO
  • Microsoft SQL Server 6.5 Standard Edition
Keywords: 
kbcode kbhowto kbinfo kbprogramming kbusage KB172117
Retired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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