Microsoft KB Archive/172117

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

Article ID: 172117

Article Last Modified on 10/16/2003

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APPLIES TO


 * Microsoft SQL Server 6.5 Standard Edition

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This article was previously published under Q172117



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 ' 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.</ul>

 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.</li>  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

</li> The conditional check "IF @debug" should not noticeably alter performance, unless the profiled stored procedure or trigger does not perform any physical disk IO.</li>  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

</li>  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. </li></ul>

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.

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

Keywords: kbhowto kbinfo kbprogramming kbcode kbusage KB172117

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