Script to check SQL Server connection pooling
Problem
Our applications are using a high number of connections and the server is very busy. How do I check whether the application is using connection pooling correctly when connecting to SQL Server? Is there an easy way to see which connections are using connection pooling and which ones are not? In this tip, I will go over how to capture this information for each logon, so you can see which connections are taking advantage of connection polling.
Solution
SQL Server 2005 introduced DDL Triggers and this solution takes advantage of the DDL Logon trigger along with the EVENTDATA() function to determine if the connections are using connection pool or NOT.
Identifying this fact is very important to every DBA as the cost of opening a connection every time data is requested is expensive. The cost of each user connection is approximately (3 * network_packet_size + 94 KB) where the default network packet size is 4 KB. That means each user connection cost is approximately 130 KB. In addition, the time it takes to make the connection can also slow down processing.
Here is the script to create a table to store the data and a DDL Logon trigger to capture this data. This should be created in the master database.
--Create the dbo.ServerLogonHistory Table
CREATE TABLE dbo.ServerLogonHistory
(
EventType VARCHAR(512),
PostTime DATETIME,
SPID INT,
ServerName VARCHAR(512),
LoginName VARCHAR(512),
LoginType VARCHAR(512),
SID VARCHAR(512),
ClientHost VARCHAR(512),
IsPooled BIT
)
GO
--Create the Logon Trigger Trigger_ServerLogon
CREATE TRIGGER Trigger_ServerLogon
ON ALL SERVER WITH EXECUTE AS 'sa' FOR LOGON
AS
BEGIN
DECLARE @data XML
SET @data = EVENTDATA()
INSERT INTO dbo.ServerLogonHistory
SELECT @data.value('(/EVENT_INSTANCE/EventType)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/PostTime)[1]', 'datetime')
, @data.value('(/EVENT_INSTANCE/SPID)[1]', 'nvarchar(4)')
, @data.value('(/EVENT_INSTANCE/ServerName)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/LoginName)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/LoginType)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/SID)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/ClientHost)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/IsPooled)[1]', 'nvarchar(1)')
END
GO
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In order for users to write to this table, that do not have rights to this table, I am using the EXECUTE AS clause in the trigger to run the code using the equivalent of the "sa" account. If you do not want to use the "sa" account another option is to create a new login, grant insert permissions to this table for this login and then use this login in the EXECUTE AS clause in the trigger.
Here is another way to do this by giving GRANT INSERT permissions to PUBLIC for table master.dbo.ServerLogonHistory.
--Create the dbo.ServerLogonHistory Table
CREATE TABLE dbo.ServerLogonHistory
(
EventType VARCHAR(512),
PostTime DATETIME,
SPID INT,
ServerName VARCHAR(512),
LoginName VARCHAR(512),
LoginType VARCHAR(512),
SID VARCHAR(512),
ClientHost VARCHAR(512),
IsPooled BIT
)
GO
--Grant insert rights to public for this table
GRANT INSERT ON dbo.ServerLogonHistory TO PUBLIC
--Create the Logon Trigger Trigger_ServerLogon
CREATE TRIGGER Trigger_ServerLogon
ON ALL SERVER FOR LOGON
AS
BEGIN
DECLARE @data XML
SET @data = EVENTDATA()
INSERT INTO dbo.ServerLogonHistory
SELECT @data.value('(/EVENT_INSTANCE/EventType)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/PostTime)[1]', 'datetime')
, @data.value('(/EVENT_INSTANCE/SPID)[1]', 'nvarchar(4)')
, @data.value('(/EVENT_INSTANCE/ServerName)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/LoginName)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/LoginType)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/SID)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/ClientHost)[1]', 'nvarchar(512)')
, @data.value('(/EVENT_INSTANCE/IsPooled)[1]', 'nvarchar(1)')
END
GO
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Here is a sample result from the data that was collected using the above DDL trigger.
You can look at the IsPooled column to check if the connections are pooled.
- 1 = pooled and
- 0 = non-pooled connections.
Next Steps:
- Here is another approach for finding connection pool information by James Rowland-Jones
- Take a look at these other DDL Triggers
- Keep on eye on this audit table, because this will track all connections to your database server and may get quite large.
- If you have any issues with LOGON triggers and you can not connect to SQL Server review this tip
Last Updated: 2009-09-04
About the author
Sankar Reddy is a Database Engineer/DBA and SQL Server MVP. He has been working with SQL Server since 2003 in a variety of roles.
View all my tips
More SQL Server Solutions
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Friday, March 04, 2016 - 6:02:39 PM - Rob Catalano
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Thanks for the script!
Use this script to delete the trigger when you have enough data.
I had to be logged in as 'SA' for the correct permissions.
DROP TRIGGER Trigger_ServerLogon ON ALL SERVER
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Tuesday, July 07, 2015 - 1:47:51 AM - Trupti
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Script to check SQL Server connection pooling
I read your connection pooling blog it helped a lot Thanks for sharing. But using same can I get SPID details as well.
I want to view which user is updating which database.In short one more column in output window with db name.
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Wednesday, September 03, 2014 - 3:05:41 AM - sawsan
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Dear,
Really useful, i tried this solution but i found tha AuditLoginTable grew exponentially, and added more than one record for each login
and every time I executed select query, the returned data increased twice.
Whad do you suggest to avoid this issue???
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Sunday, January 16, 2011 - 6:31:49 AM - Yaniv Etrogi
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Good article.
I would like to point out that another approach exists and that is via sql server trace. For a detailed explanation you can visit this link:
http://blogs.microsoft.co.il/blogs/yaniv_etrogi/archive/2009/02/23/detecting-none-pooled-logins.aspx
-Yaniv
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Monday, August 16, 2010 - 2:06:53 PM - admin
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Thanks Richard for pointing that out. This has been updated to reflect the correct author.
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Monday, August 16, 2010 - 11:21:45 AM - Vishal Gamji
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Nice tip. Really useful. Thanks.
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Friday, August 13, 2010 - 7:27:31 AM - Richard Douglas
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In the next steps section it states there is another approach by Jamie Thompson, however the link is to James Rowland-Jones's blog :-)
You should change the text to give credit to the right person.
Rich
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