Getting pool statistics

[NiKiZe]

Hi,
I use this hack for MySql.Data to get stats on the connection pool thru reflection.
Totally understanding that this is in no way supported, I still wonder if I could get some pointers on where similar values might exist in MySqlConnector ?

Logic psuedo explained:

• Grab ConnectionPool object using connection string, since that is the unique key
• Pull out Available "pool slots", inUse connections in pool, idle connections in pool

        public int[] GetPoolStatsViaReflection()
        {
            var asm = typeof(MySqlConnectionStringBuilder).Assembly;
            var poolManagerType = asm.GetType("MySql.Data.MySqlClient.MySqlPoolManager"); // internal sealed
            var poolType = asm.GetType("MySql.Data.MySqlClient.MySqlPool"); // internal sealed

            var pool = poolManagerType.InvokeMember("GetPool", System.Reflection.BindingFlags.InvokeMethod | System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Public, null, null, new object[] { this.connectionStringBuilder });

            const System.Reflection.BindingFlags nonPublicInstanceField = System.Reflection.BindingFlags.GetField | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance;
            var totalAvailable = (int)poolType.InvokeMember("available", nonPublicInstanceField, null, pool, new object[] { });
            // List<Driver>
            var inUsePool = (System.Collections.ICollection)poolType.InvokeMember("inUsePool", nonPublicInstanceField, null, pool, new object[] { });
            // Queue<Driver>
            var idlePool = (System.Collections.ICollection)poolType.InvokeMember("idlePool", nonPublicInstanceField, null, pool, new object[] { });

            return new[] {totalAvailable, inUsePool.Count, idlePool.Count};
        }

I guess this lives in MySqlConnector.Core.ConnectionPool and maybe m_leasedSessions is similar to inUsePool?

[bgrainger]

Related: #491

[bgrainger]

MySqlConnector.Core.ConnectionPool.s_pools will contain all known connection pools:

MySqlConnector/src/MySqlConnector/Core/ConnectionPool.cs

Line 600 in 62ad22d

private static readonly ConcurrentDictionary<string, ConnectionPool?> s_pools = new();

MySqlConnector.Core.ConnectionPool.m_sessions.Count has the number of idle (pooled) sessions:

MySqlConnector/src/MySqlConnector/Core/ConnectionPool.cs

Line 607 in 62ad22d

private readonly LinkedList<ServerSession> m_sessions;

MySqlConnector.Core.ConnectionPool.m_leasedSessions.Count has the number of active (in-use) sessions:

MySqlConnector/src/MySqlConnector/Core/ConnectionPool.cs

Line 608 in 62ad22d

private readonly Dictionary<string, ServerSession> m_leasedSessions;

MySqlConnector.Core.ConnectionPool.ConnectionSettings.MaximumPoolSize contains the maximum number of active connections that can be created:

MySqlConnector/src/MySqlConnector/Core/ConnectionPool.cs

Line 13 in 62ad22d

public ConnectionSettings ConnectionSettings { get; }

MySqlConnector/src/MySqlConnector/Core/ConnectionSettings.cs

Line 215 in 62ad22d

public int MaximumPoolSize { get; }

I'm sure it goes without saying but this is completely unsupported. Moreover, this is highly concurrent code, and some of these properties are not safe to read when there are concurrent writers.

[NiKiZe]

Fantastic, thanks!
I have not yet seen any issue with getting counts without locks (not thinking about getting missmatching values)
Saying it again absolutely unsupported, The usecase is to grab some data on exceptions. So should be rare.

Initial implementation:

            var asm = typeof(MySqlConnectionStringBuilder).Assembly;
            const string MySqlCoreName = "MySqlConnector." + nameof(MySqlConnector.Core);
            var poolType = asm.GetType(MySqlCoreName + ".ConnectionPool"); // internal sealed
            var settingType = asm.GetType(MySqlCoreName + ".ConnectionSettings"); // internal sealed

            var pool = poolType.InvokeMember("GetPool", System.Reflection.BindingFlags.InvokeMethod | System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Public, null, null, new object[] { this.connectionStringBuilder.ConnectionString });

            const System.Reflection.BindingFlags nonPublicInstanceField = System.Reflection.BindingFlags.GetField | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance;
            var settings = poolType.InvokeMember("ConnectionSettings", nonPublicInstanceField | System.Reflection.BindingFlags.GetProperty, null, pool, new object[] { });
            var maxPoolSize = (int)settingType.InvokeMember("MaximumPoolSize", nonPublicInstanceField | System.Reflection.BindingFlags.GetProperty, null, settings, new object[] { });
            // Dictionary<string, ServerSession> // has the number of active (in-use) sessions:
            var inUse = (System.Collections.ICollection)poolType.InvokeMember("m_leasedSessions", nonPublicInstanceField, null, pool, new object[] { });
            // LinkedList<ServerSession> // has the number of idle (pooled) sessions:
            var idle = (System.Collections.ICollection)poolType.InvokeMember("m_sessions", nonPublicInstanceField, null, pool, new object[] { });

            var inUseCount = inUse.Count;
            var idleCount = idle.Count;

            return new[] { maxPoolSize - inUseCount, inUseCount, idleCount };