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

ID: Q172117

The information in this article applies to:

Microsoft SQL Server version 6.5

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:

Q111405 : 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:

Q165951 : 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:

Simple Transact-SQL Time Profiling

Simple Table-Based Stored Procedure and Trigger Profiling

Advanced Table-Based Stored Procedure and Trigger Profiling

Sample Stored Procedure to Manage Advanced Table-Based Profiling

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.

Additional query words: tsql transql t-sql tran-sql rpc RPCs

Keywords : kbcode kbprg kbusage SSrvProg SSrvStProc SSrvTran_SQL
Version : 6.5
Platform : WINDOWS
Issue type : kbhowto kbinfo