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This is my database connection string. I did not set max pool size until now.

public static string srConnectionString = 
                       "server=localhost;database=mydb;uid=sa;pwd=mypw;";

So currently how many connections does my application support? What is the correct syntax for increasing the connection pool size?

The application is written in C# 4.0.

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3
  • 11
    if you don't have a problem, leave it as the default.
    – Mitch Wheat
    Commented Oct 16, 2011 at 12:01
  • currently yes but i think it might cause problems at peak moments. So i prefer set higher than default. as i read default is 100 am i right ?
    – Furkan Gözükara
    Commented Oct 16, 2011 at 12:03
  • 4
    The default Connection Pool size of 100 is documented by Microsoft at learn.microsoft.com/en-us/dotnet/framework/data/adonet/… and likely other places.
    – Henry Troup
    Commented Oct 19, 2017 at 14:58

3 Answers 3

Reset to default
110

Currently your application support 100 connections in pool. Here is what conn string will look like if you want to increase it to 200:

public static string srConnectionString = 
                "server=localhost;database=mydb;uid=sa;pwd=mypw;Max Pool Size=200;";

You can investigate how many connections with database your application use, by executing sp_who procedure in your database. In most cases default connection pool size will be enough.

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  • 4
    Is there another way of setting the Max and Min poolsize than via the connectionstring? I would prefer to do it in code...
    – Jos
    Commented Oct 23, 2012 at 12:06
  • What happens when setting the 'max pool size' to, let say 30. When all the slots filled with 'in-use' and 'idle connections', will the idle connections be closed automatically to make room for new connections?
    – Pierre
    Commented Feb 22, 2016 at 12:54
  • 5
    @Pierre - you'll receive an error similar to the following: System.InvalidOperationException: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached. at System.Data.SqlClient.SqlConnectionPoolManager.GetPooledConnection(SqlConnectionString options, Boolean& isInTransaction) at System.Data.SqlClient.SqlConnection.Open()
    – Caleb Seadon
    Commented Aug 7, 2017 at 23:17
  • What is your reference for 100 connections by default?
    – Mahmoud Moravej
    Commented Oct 10, 2017 at 14:20
  • The first paragraph of the "Adding Connections" section of the Documentation article SQL Server Connection Pooling (ADO.NET) states that 100 is the default max pool size. (learn.microsoft.com/en-us/dotnet/framework/data/adonet/…) Seen 2019-09-14
    – Jahaziel
    Commented Oct 14, 2019 at 16:13
17

"currently yes but i think it might cause problems at peak moments" I can confirm, that I had a problem where I got timeouts because of peak requests. After I set the max pool size, the application ran without any problems. IIS 7.5 / ASP.Net

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  • 5
    This is not an answer
    – Kellen Stuart
    Commented Sep 3, 2020 at 3:32
-7

We can define maximum pool size in following way:

                <pool> 
               <min-pool-size>5</min-pool-size>
                <max-pool-size>200</max-pool-size>
                <prefill>true</prefill>
                <use-strict-min>true</use-strict-min>
                <flush-strategy>IdleConnections</flush-strategy>
                </pool>
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  • 2
    What file is this?
    – Jon Schneider
    Commented Jun 15, 2020 at 13:49
  • it is not clear that what file is this, if it is a webconfig then where should we add this <pool> tag.
    – Muhammad Ashhar Hasan
    Commented Aug 23, 2021 at 9:33

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