| Bug #24373 | High CPU utilization when no idle connection | ||
|---|---|---|---|
| Submitted: | 16 Nov 2006 21:35 | Modified: | 27 Feb 2007 11:19 |
| Reporter: | Karl Seguin | Email Updates: | |
| Status: | Closed | Impact on me: | |
| Category: | Connector / NET | Severity: | S5 (Performance) |
| Version: | 5.0.x | OS: | Windows (Win32) |
| Assigned to: | CPU Architecture: | Any | |
| Tags: | .net, pooling, timeout | ||
[16 Nov 2006 21:45]
Karl Seguin
Sorry, the last point about "CreateNewPooledConnection" was just an unrelated remark...
[22 Nov 2006 12:21]
Tonci Grgin
Karl, thanks for your excellent problem report. Verified as described by reporter with latest sources. Until timeout expires, CPU is locked at 100%: Connecting to Mysql DB error connecting: Timeout expired. The timeout period elapsed prior to obtainin g a connection from the pool. This may have occurred because all pooled connect ions were in use and max pool size was reached.
[22 Nov 2006 12:22]
Tonci Grgin
Test case
Attachment: Program.cs (text/plain), 1.50 KiB.
[22 Feb 2007 20:06]
Bugs System
A patch for this bug has been committed. After review, it may be pushed to the relevant source trees for release in the next version. You can access the patch from: http://lists.mysql.com/commits/20413
[22 Feb 2007 20:07]
Reggie Burnett
Fixed in 1.0.10 and 5.0.4
[22 Feb 2007 20:52]
Bugs System
A patch for this bug has been committed. After review, it may be pushed to the relevant source trees for release in the next version. You can access the patch from: http://lists.mysql.com/commits/20420
[27 Feb 2007 11:19]
MC Brown
A note has been added to the 5.0.4 and 1.0.10 changelogs.
Description: MySqlPool.GetConnection runs a very tight loop until there's either a timeout or a connection is retrieved from the pool. Specifically: while (driver == null && (Environment.TickCount - startTime) < timeOut) { driver = GetPooledConnection(); } private Driver GetPooledConnection() { while (idlePool.Count <= 0) { if (inUsePool.Count == maxSize) { return null; } CreateNewPooledConnection(); } return CheckoutConnection(); } If there are no idle connections in idlePool and we are using the maximum amount of connections, we'll just spin our wheels in the loop. This can have a pretty harsh performance impact on a system which is pushing up against it's connection limit. How to repeat: This code will reproduce the problem each time. Using a profiler, perfmon or just task-manager, we can see the impact on performance this code will have. I used snippet compiler, so WL and RL just map to Console.WriteLine and Console.ReadLine . private const string _connectionString = "XXXXXX;Maximum Pool Size=1"; public static void Main() { MySqlConnection connection1 = null; MySqlConnection connection2 = null; try { connection1 = GetConnection(); connection2 = GetConnection(); } catch(Exception ex) { WL(ex); } finally { if (connection1 != null) { connection1.Dispose(); } if (connection2 != null) { connection2.Dispose(); } } WL("Done"); RL(); } private static MySqlConnection GetConnection() { MySqlConnection connection = new MySqlConnection(_connectionString); connection.Open(); return connection; } Suggested fix: I don't know what people think about sleeping inside the while loop... Ideally it'd be nice to see this block and wait for a signal that a connection has become available. From a performance standpoint, it'd be nice if CreateNewPooledConnection() actually Checkedout and returned the connection directly. As is, 1 thread can keep creating new pool connections while other threads sneak in and steal them.