From c9ed8503ff07a07227c5bc640010ca1bdf27817e Mon Sep 17 00:00:00 2001
From: KirillKurdyukov <kurdyukov-kir@ydb.tech>
Date: Thu, 17 Jul 2025 13:20:21 +0300
Subject: [PATCH 1/6] feat: PoolingSessionSource 2.0 based on Npgsql pooling
 algorithm

---
 src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs     | 4 ++--
 src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs b/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs
index 9669afb1..bbe3ce0d 100644
--- a/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs
+++ b/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs
@@ -232,7 +232,7 @@ StringBuilder yql
                         return startToken; // rollback parse IN LIST
                     }
 
-                    yql.Append(listStartToken > startToken ? sql[startToken .. listStartToken] : ' ');
+                    yql.Append(listStartToken > startToken ? sql[startToken..listStartToken] : ' ');
                     var paramListName = sqlParamsBuilder.AddListPrimitiveParams(findNameParams);
                     yql.Append(paramListName);
 
@@ -273,7 +273,7 @@ private static (string Name, int NextToken) ParseNameParam(string sql, int curTo
             throw new YdbException($"Have empty name parameter, invalid SQL [position: {prevToken}]");
         }
 
-        return ($"${sql[prevToken .. curToken]}", curToken);
+        return ($"${sql[prevToken..curToken]}", curToken);
     }
 
     private static bool IsSqlIdentifierChar(this char c) => char.IsLetterOrDigit(c) || c == '_';
diff --git a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
index 2002ec69..babf7780 100644
--- a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
@@ -1,3 +1,8 @@
+// This file contains session pooling algorithms adapted from Npgsql
+// Original source: https://github.com/npgsql/npgsql
+// Copyright (c) 2002-2025, Npgsql
+// Licence https://github.com/npgsql/npgsql?tab=PostgreSQL-1-ov-file
+
 using Microsoft.Extensions.Logging;
 using Ydb.Query;
 using Ydb.Query.V1;

From 7dd5c88007c3b66d46e498916e42307c1e6cadc0 Mon Sep 17 00:00:00 2001
From: KirillKurdyukov <kurdyukov-kir@ydb.tech>
Date: Tue, 22 Jul 2025 17:04:02 +0300
Subject: [PATCH 2/6] dev: Prepare ISession for switching implementation.

---
 src/Ydb.Sdk/src/Ado/PoolManager.cs            |  3 +-
 src/Ydb.Sdk/src/Ado/Session/ISession.cs       |  2 +
 .../src/Ado/Session/ImplicitSession.cs        |  7 +-
 src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs | 27 ++++---
 src/Ydb.Sdk/src/Ado/YdbAdoDefaultSettings.cs  | 12 ----
 src/Ydb.Sdk/src/Ado/YdbCommand.cs             |  4 +-
 src/Ydb.Sdk/src/Ado/YdbConnection.cs          |  9 +--
 .../src/Ado/YdbConnectionStringBuilder.cs     |  8 +--
 src/Ydb.Sdk/src/Ado/YdbSchema.cs              | 60 +++++++++-------
 src/Ydb.Sdk/src/Pool/SessionPool.cs           | 11 +--
 src/Ydb.Sdk/src/Services/Query/SessionPool.cs | 70 +++++++------------
 .../SessionSourceBenchmark.cs                 |  2 +
 .../StressTestTank.cs                         |  7 +-
 .../Session/PoolingSessionSourceMockTests.cs  | 15 ++--
 14 files changed, 109 insertions(+), 128 deletions(-)
 delete mode 100644 src/Ydb.Sdk/src/Ado/YdbAdoDefaultSettings.cs

diff --git a/src/Ydb.Sdk/src/Ado/PoolManager.cs b/src/Ydb.Sdk/src/Ado/PoolManager.cs
index ed2712d6..a8f787b4 100644
--- a/src/Ydb.Sdk/src/Ado/PoolManager.cs
+++ b/src/Ydb.Sdk/src/Ado/PoolManager.cs
@@ -1,4 +1,5 @@
 using System.Collections.Concurrent;
+using Ydb.Sdk.Ado.Session;
 using Ydb.Sdk.Pool;
 using Ydb.Sdk.Services.Query;
 
@@ -9,7 +10,7 @@ internal static class PoolManager
     private static readonly SemaphoreSlim SemaphoreSlim = new(1); // async mutex
     private static readonly ConcurrentDictionary<string, SessionPool> Pools = new();
 
-    internal static async Task<Services.Query.Session> GetSession(
+    internal static async Task<ISession> GetSession(
         YdbConnectionStringBuilder connectionString,
         CancellationToken cancellationToken
     )
diff --git a/src/Ydb.Sdk/src/Ado/Session/ISession.cs b/src/Ydb.Sdk/src/Ado/Session/ISession.cs
index fc8c70ba..1aec418b 100644
--- a/src/Ydb.Sdk/src/Ado/Session/ISession.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/ISession.cs
@@ -6,6 +6,8 @@ namespace Ydb.Sdk.Ado.Session;
 
 internal interface ISession
 {
+    IDriver Driver { get; }
+
     bool IsBroken { get; }
 
     ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
diff --git a/src/Ydb.Sdk/src/Ado/Session/ImplicitSession.cs b/src/Ydb.Sdk/src/Ado/Session/ImplicitSession.cs
index 182dbf44..45a251f7 100644
--- a/src/Ydb.Sdk/src/Ado/Session/ImplicitSession.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/ImplicitSession.cs
@@ -6,13 +6,12 @@ namespace Ydb.Sdk.Ado.Session;
 
 internal class ImplicitSession : ISession
 {
-    private readonly IDriver _driver;
-
     public ImplicitSession(IDriver driver)
     {
-        _driver = driver;
+        Driver = driver;
     }
 
+    public IDriver Driver { get; }
     public bool IsBroken => false;
 
     public ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
@@ -36,7 +35,7 @@ public ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
         };
         request.Parameters.Add(parameters.ToDictionary(p => p.Key, p => p.Value.GetProto()));
 
-        return _driver.ServerStreamCall(QueryService.ExecuteQueryMethod, request, settings);
+        return Driver.ServerStreamCall(QueryService.ExecuteQueryMethod, request, settings);
     }
 
     public Task CommitTransaction(string txId, CancellationToken cancellationToken = default) =>
diff --git a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
index babf7780..ed85d411 100644
--- a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
@@ -20,9 +20,9 @@ internal class PoolingSession : IPoolingSession
     private static readonly TimeSpan DeleteSessionTimeout = TimeSpan.FromSeconds(5);
     private static readonly CreateSessionRequest CreateSessionRequest = new();
 
-    private readonly IDriver _driver;
     private readonly PoolingSessionSource _poolingSessionSource;
     private readonly ILogger<PoolingSession> _logger;
+    private readonly CancellationTokenSource _attachStreamLifecycleCts = new();
 
     private volatile bool _isBroken = true;
 
@@ -31,6 +31,7 @@ internal class PoolingSession : IPoolingSession
     private string SessionId { get; set; } = string.Empty;
     private long NodeId { get; set; }
 
+    public IDriver Driver { get; }
     public bool IsBroken => _isBroken;
 
     internal PoolingSession(
@@ -40,10 +41,10 @@ internal PoolingSession(
         ILogger<PoolingSession> logger
     )
     {
-        _driver = driver;
         _poolingSessionSource = poolingSessionSource;
         _disableServerBalancer = disableServerBalancer;
         _logger = logger;
+        Driver = driver;
     }
 
     public ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
@@ -65,7 +66,7 @@ public ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
         };
         request.Parameters.Add(parameters.ToDictionary(p => p.Key, p => p.Value.GetProto()));
 
-        return _driver.ServerStreamCall(QueryService.ExecuteQueryMethod, request, settings);
+        return Driver.ServerStreamCall(QueryService.ExecuteQueryMethod, request, settings);
     }
 
     public async Task CommitTransaction(
@@ -73,7 +74,7 @@ public async Task CommitTransaction(
         CancellationToken cancellationToken = default
     )
     {
-        var response = await _driver.UnaryCall(
+        var response = await Driver.UnaryCall(
             QueryService.CommitTransactionMethod,
             new CommitTransactionRequest { SessionId = SessionId, TxId = txId },
             new GrpcRequestSettings { CancellationToken = cancellationToken, NodeId = NodeId }
@@ -90,7 +91,7 @@ public async Task RollbackTransaction(
         CancellationToken cancellationToken = default
     )
     {
-        var response = await _driver.UnaryCall(
+        var response = await Driver.UnaryCall(
             QueryService.RollbackTransactionMethod,
             new RollbackTransactionRequest { SessionId = SessionId, TxId = txId },
             new GrpcRequestSettings { CancellationToken = cancellationToken, NodeId = NodeId }
@@ -126,7 +127,7 @@ public async Task Open(CancellationToken cancellationToken)
             requestSettings.ClientCapabilities.Add(SessionBalancer);
         }
 
-        var response = await _driver.UnaryCall(QueryService.CreateSessionMethod, CreateSessionRequest, requestSettings);
+        var response = await Driver.UnaryCall(QueryService.CreateSessionMethod, CreateSessionRequest, requestSettings);
 
         if (response.Status.IsNotSuccess())
         {
@@ -143,7 +144,7 @@ public async Task Open(CancellationToken cancellationToken)
         {
             try
             {
-                using var stream = await _driver.ServerStreamCall(
+                using var stream = await Driver.ServerStreamCall(
                     QueryService.AttachSessionMethod,
                     new AttachSessionRequest { SessionId = SessionId },
                     new GrpcRequestSettings { NodeId = NodeId }
@@ -166,10 +167,12 @@ public async Task Open(CancellationToken cancellationToken)
 
                 completeTask.SetResult();
 
+                var lifecycleAttachToken = _attachStreamLifecycleCts.Token;
+
                 try
                 {
                     // ReSharper disable once MethodSupportsCancellation
-                    while (await stream.MoveNextAsync())
+                    while (await stream.MoveNextAsync(lifecycleAttachToken))
                     {
                         var sessionState = stream.Current;
 
@@ -220,14 +223,10 @@ public async Task DeleteSession()
     {
         try
         {
-            if (_isBroken)
-            {
-                return;
-            }
-
             _isBroken = true;
+            _attachStreamLifecycleCts.CancelAfter(DeleteSessionTimeout);
 
-            var deleteSessionResponse = await _driver.UnaryCall(
+            var deleteSessionResponse = await Driver.UnaryCall(
                 QueryService.DeleteSessionMethod,
                 new DeleteSessionRequest { SessionId = SessionId },
                 new GrpcRequestSettings { TransportTimeout = DeleteSessionTimeout, NodeId = NodeId }
diff --git a/src/Ydb.Sdk/src/Ado/YdbAdoDefaultSettings.cs b/src/Ydb.Sdk/src/Ado/YdbAdoDefaultSettings.cs
deleted file mode 100644
index 6c20df0b..00000000
--- a/src/Ydb.Sdk/src/Ado/YdbAdoDefaultSettings.cs
+++ /dev/null
@@ -1,12 +0,0 @@
-namespace Ydb.Sdk.Ado;
-
-internal static class YdbAdoDefaultSettings
-{
-    internal const string Host = "localhost";
-
-    internal const int Port = 2136;
-
-    internal const string Database = "/local";
-
-    internal const bool UseTls = false;
-}
diff --git a/src/Ydb.Sdk/src/Ado/YdbCommand.cs b/src/Ydb.Sdk/src/Ado/YdbCommand.cs
index 844343b5..ec49c0fa 100644
--- a/src/Ydb.Sdk/src/Ado/YdbCommand.cs
+++ b/src/Ydb.Sdk/src/Ado/YdbCommand.cs
@@ -206,8 +206,8 @@ protected override async Task<DbDataReader> ExecuteDbDataReaderAsync(CommandBeha
         preparedSql.Append(sql);
 
         var execSettings = CommandTimeout > 0
-            ? new ExecuteQuerySettings { TransportTimeout = TimeSpan.FromSeconds(CommandTimeout) }
-            : new ExecuteQuerySettings();
+            ? new GrpcRequestSettings { TransportTimeout = TimeSpan.FromSeconds(CommandTimeout) }
+            : new GrpcRequestSettings();
 
         var transaction = YdbConnection.CurrentTransaction;
 
diff --git a/src/Ydb.Sdk/src/Ado/YdbConnection.cs b/src/Ydb.Sdk/src/Ado/YdbConnection.cs
index 8cac45c2..ce2e2c43 100644
--- a/src/Ydb.Sdk/src/Ado/YdbConnection.cs
+++ b/src/Ydb.Sdk/src/Ado/YdbConnection.cs
@@ -1,6 +1,7 @@
 using System.Data;
 using System.Data.Common;
 using System.Diagnostics.CodeAnalysis;
+using Ydb.Sdk.Ado.Session;
 using Ydb.Sdk.Services.Query;
 using static System.Data.IsolationLevel;
 
@@ -24,7 +25,7 @@ private YdbConnectionStringBuilder ConnectionStringBuilder
         [param: AllowNull] init => _connectionStringBuilder = value;
     }
 
-    internal Services.Query.Session Session
+    internal ISession Session
     {
         get
         {
@@ -35,7 +36,7 @@ internal Services.Query.Session Session
         private set => _session = value;
     }
 
-    private Services.Query.Session _session = null!;
+    private ISession _session = null!;
 
     public YdbConnection()
     {
@@ -124,7 +125,7 @@ public override async Task CloseAsync()
         }
         finally
         {
-            await _session.Release();
+            _session.Close();
         }
     }
 
@@ -152,7 +153,7 @@ internal void OnNotSuccessStatusCode(StatusCode code)
     {
         _session.OnNotSuccessStatusCode(code);
 
-        if (!_session.IsActive)
+        if (_session.IsBroken)
         {
             ConnectionState = ConnectionState.Broken;
         }
diff --git a/src/Ydb.Sdk/src/Ado/YdbConnectionStringBuilder.cs b/src/Ydb.Sdk/src/Ado/YdbConnectionStringBuilder.cs
index 68c5849f..4f5dab33 100644
--- a/src/Ydb.Sdk/src/Ado/YdbConnectionStringBuilder.cs
+++ b/src/Ydb.Sdk/src/Ado/YdbConnectionStringBuilder.cs
@@ -25,15 +25,15 @@ public YdbConnectionStringBuilder(string connectionString)
     // Init default connection string
     private void InitDefaultValues()
     {
-        _host = YdbAdoDefaultSettings.Host;
-        _port = YdbAdoDefaultSettings.Port;
-        _database = YdbAdoDefaultSettings.Database;
+        _host = "localhost";
+        _port = 2136;
+        _database = "/local";
         _minSessionPool = 0;
         _maxSessionPool = SessionPoolDefaultSettings.MaxSessionPool;
         _createSessionTimeout = SessionPoolDefaultSettings.CreateSessionTimeoutSeconds;
         _sessionIdleTimeout = 300;
         _sessionPruningInterval = 10;
-        _useTls = YdbAdoDefaultSettings.UseTls;
+        _useTls = false;
         _connectTimeout = GrpcDefaultSettings.ConnectTimeoutSeconds;
         _keepAlivePingDelay = GrpcDefaultSettings.KeepAlivePingSeconds;
         _keepAlivePingTimeout = GrpcDefaultSettings.KeepAlivePingTimeoutSeconds;
diff --git a/src/Ydb.Sdk/src/Ado/YdbSchema.cs b/src/Ydb.Sdk/src/Ado/YdbSchema.cs
index 4fb1d901..eb2a2823 100644
--- a/src/Ydb.Sdk/src/Ado/YdbSchema.cs
+++ b/src/Ydb.Sdk/src/Ado/YdbSchema.cs
@@ -3,8 +3,11 @@
 using System.Globalization;
 using Ydb.Scheme;
 using Ydb.Scheme.V1;
+using Ydb.Sdk.Ado.Internal;
 using Ydb.Sdk.Ado.Schema;
 using Ydb.Sdk.Services.Table;
+using Ydb.Table;
+using Ydb.Table.V1;
 
 namespace Ydb.Sdk.Ado;
 
@@ -59,10 +62,28 @@ public static async Task<YdbTable> DescribeTable(
     {
         try
         {
-            var describeResponse = await ydbConnection.Session
-                .DescribeTable(WithSuffix(ydbConnection.Database) + tableName, describeTableSettings);
+            describeTableSettings ??= new DescribeTableSettings();
 
-            return new YdbTable(tableName, describeResponse);
+            var describeResponse = await ydbConnection.Session.Driver.UnaryCall(
+                TableService.DescribeTableMethod,
+                new DescribeTableRequest
+                {
+                    Path = WithSuffix(ydbConnection.Database) + tableName,
+                    IncludeTableStats = describeTableSettings.IncludeTableStats,
+                    IncludePartitionStats = describeTableSettings.IncludePartitionStats,
+                    IncludeShardKeyBounds = describeTableSettings.IncludeShardKeyBounds
+                },
+                describeTableSettings
+            );
+
+            if (describeResponse.Operation.Status.IsNotSuccess())
+            {
+                throw YdbException.FromServer(describeResponse.Operation.Status, describeResponse.Operation.Issues);
+            }
+
+            var describeResult = describeResponse.Operation.Result.Unpack<DescribeTableResult>();
+
+            return new YdbTable(tableName, describeResult);
         }
         catch (YdbException e)
         {
@@ -241,31 +262,20 @@ private static async Task AppendDescribeTable(
         string? tableType,
         Action<YdbTable, string> appendInTable)
     {
-        try
-        {
-            var describeResponse = await ydbConnection.Session
-                .DescribeTable(WithSuffix(ydbConnection.Database) + tableName, describeTableSettings);
-            var ydbTable = new YdbTable(tableName, describeResponse);
+        var ydbTable = await DescribeTable(ydbConnection, tableName, describeTableSettings);
 
-            var type = ydbTable.IsSystem
-                ? "SYSTEM_TABLE"
-                : ydbTable.Type switch
-                {
-                    YdbTable.TableType.Table => "TABLE",
-                    YdbTable.TableType.ColumnTable => "COLUMN_TABLE",
-                    YdbTable.TableType.ExternalTable => "EXTERNAL_TABLE",
-                    _ => throw new ArgumentOutOfRangeException(nameof(tableType))
-                };
-            if (type.IsPattern(tableType))
+        var type = ydbTable.IsSystem
+            ? "SYSTEM_TABLE"
+            : ydbTable.Type switch
             {
-                appendInTable(ydbTable, type);
-            }
-        }
-        catch (YdbException e)
+                YdbTable.TableType.Table => "TABLE",
+                YdbTable.TableType.ColumnTable => "COLUMN_TABLE",
+                YdbTable.TableType.ExternalTable => "EXTERNAL_TABLE",
+                _ => throw new ArgumentOutOfRangeException(nameof(tableType))
+            };
+        if (type.IsPattern(tableType))
         {
-            ydbConnection.OnNotSuccessStatusCode(e.Code);
-
-            throw;
+            appendInTable(ydbTable, type);
         }
     }
 
diff --git a/src/Ydb.Sdk/src/Pool/SessionPool.cs b/src/Ydb.Sdk/src/Pool/SessionPool.cs
index 28feb64e..b7e82dd6 100644
--- a/src/Ydb.Sdk/src/Pool/SessionPool.cs
+++ b/src/Ydb.Sdk/src/Pool/SessionPool.cs
@@ -57,6 +57,8 @@ internal async Task<TSession> GetSession(CancellationToken cancellationToken = d
             if (session != null) // not active
             {
                 Logger.LogDebug("Session[{Id}] isn't active, creating new session", session.SessionId);
+
+                _ = DeleteSession(session);
             }
 
             try
@@ -149,6 +151,10 @@ internal async ValueTask ReleaseSession(TSession session)
             {
                 _idleSessions.Enqueue(session);
             }
+            else
+            {
+                _ = DeleteSession(session);
+            }
         }
         finally
         {
@@ -162,10 +168,7 @@ private async Task DeleteSession(TSession session)
     {
         try
         {
-            if (session.IsActive)
-            {
-                await session.DeleteSession();
-            }
+            await session.DeleteSession();
         }
         catch (YdbException e)
         {
diff --git a/src/Ydb.Sdk/src/Services/Query/SessionPool.cs b/src/Ydb.Sdk/src/Services/Query/SessionPool.cs
index 2c496b06..d843fae0 100644
--- a/src/Ydb.Sdk/src/Services/Query/SessionPool.cs
+++ b/src/Ydb.Sdk/src/Services/Query/SessionPool.cs
@@ -3,11 +3,9 @@
 using Ydb.Query.V1;
 using Ydb.Sdk.Ado;
 using Ydb.Sdk.Ado.Internal;
+using Ydb.Sdk.Ado.Session;
 using Ydb.Sdk.Pool;
-using Ydb.Sdk.Services.Table;
 using Ydb.Sdk.Value;
-using Ydb.Table;
-using Ydb.Table.V1;
 using CommitTransactionRequest = Ydb.Query.CommitTransactionRequest;
 using CreateSessionRequest = Ydb.Query.CreateSessionRequest;
 using DeleteSessionRequest = Ydb.Query.DeleteSessionRequest;
@@ -20,14 +18,15 @@ internal sealed class SessionPool : SessionPool<Session>, IAsyncDisposable
 {
     private static readonly CreateSessionRequest CreateSessionRequest = new();
 
-    private readonly IDriver _driver;
     private readonly bool _disposingDriver;
     private readonly ILogger<Session> _loggerSession;
 
+    internal readonly IDriver Driver;
+
     internal SessionPool(IDriver driver, SessionPoolConfig sessionPoolConfig)
         : base(driver.LoggerFactory.CreateLogger<SessionPool>(), sessionPoolConfig)
     {
-        _driver = driver;
+        Driver = driver;
         _disposingDriver = sessionPoolConfig.DisposeDriver;
         _loggerSession = driver.LoggerFactory.CreateLogger<Session>();
     }
@@ -46,7 +45,7 @@ protected override async Task<Session> CreateSession(
             requestSettings.ClientCapabilities.Add("session-balancer");
         }
 
-        var response = await _driver.UnaryCall(
+        var response = await Driver.UnaryCall(
             QueryService.CreateSessionMethod,
             CreateSessionRequest,
             requestSettings
@@ -59,13 +58,13 @@ protected override async Task<Session> CreateSession(
         var sessionId = response.SessionId;
         var nodeId = response.NodeId;
 
-        var session = new Session(_driver, this, sessionId, nodeId, _loggerSession);
+        var session = new Session(Driver, this, sessionId, nodeId, _loggerSession);
 
         _ = Task.Run(async () =>
         {
             try
             {
-                using var stream = await _driver.ServerStreamCall(
+                using var stream = await Driver.ServerStreamCall(
                     QueryService.AttachSessionMethod,
                     new AttachSessionRequest { SessionId = sessionId },
                     new GrpcRequestSettings { NodeId = nodeId }
@@ -138,13 +137,11 @@ protected override async Task<Session> CreateSession(
         return session;
     }
 
-    protected override ValueTask DisposeDriver() => _disposingDriver ? _driver.DisposeAsync() : default;
+    protected override ValueTask DisposeDriver() => _disposingDriver ? Driver.DisposeAsync() : default;
 }
 
-internal class Session : SessionBase<Session>
+internal class Session : SessionBase<Session>, ISession
 {
-    internal IDriver Driver { get; }
-
     internal Session(
         IDriver driver,
         SessionPool<Session> sessionPool,
@@ -156,20 +153,21 @@ ILogger<Session> logger
         Driver = driver;
     }
 
-    internal ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
-        string query,
-        Dictionary<string, YdbValue>? parameters,
-        ExecuteQuerySettings? settings,
+    public IDriver Driver { get; }
+
+    public ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
+        string query, 
+        Dictionary<string, YdbValue> parameters, 
+        GrpcRequestSettings settings,
         TransactionControl? txControl)
     {
-        parameters ??= new Dictionary<string, YdbValue>();
-        settings = MakeGrpcRequestSettings(settings ?? new ExecuteQuerySettings());
+        settings = MakeGrpcRequestSettings(settings);
 
         var request = new ExecuteQueryRequest
         {
             SessionId = SessionId,
             ExecMode = ExecMode.Execute,
-            QueryContent = new QueryContent { Text = query, Syntax = (Ydb.Query.Syntax)settings.Syntax },
+            QueryContent = new QueryContent { Text = query, Syntax = Ydb.Query.Syntax.YqlV1 },
             StatsMode = StatsMode.None,
             TxControl = txControl
         };
@@ -179,7 +177,13 @@ internal ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
         return Driver.ServerStreamCall(QueryService.ExecuteQueryMethod, request, settings);
     }
 
-    internal async Task CommitTransaction(string txId, CancellationToken cancellationToken = default)
+    public bool IsBroken => !IsActive;
+
+    public new void OnNotSuccessStatusCode(StatusCode code) => base.OnNotSuccessStatusCode(code);
+
+    public void Close() => Release();
+
+    public async Task CommitTransaction(string txId, CancellationToken cancellationToken = default)
     {
         var settings = MakeGrpcRequestSettings(new GrpcRequestSettings { CancellationToken = cancellationToken });
 
@@ -192,7 +196,7 @@ internal async Task CommitTransaction(string txId, CancellationToken cancellatio
         }
     }
 
-    internal async Task RollbackTransaction(string txId, CancellationToken cancellationToken = default)
+    public async Task RollbackTransaction(string txId, CancellationToken cancellationToken = default)
     {
         var settings = MakeGrpcRequestSettings(new GrpcRequestSettings { CancellationToken = cancellationToken });
 
@@ -205,30 +209,6 @@ internal async Task RollbackTransaction(string txId, CancellationToken cancellat
         }
     }
 
-    internal async Task<DescribeTableResult> DescribeTable(string path, DescribeTableSettings? settings = null)
-    {
-        settings = MakeGrpcRequestSettings(settings ?? new DescribeTableSettings());
-
-        var response = await Driver.UnaryCall(
-            TableService.DescribeTableMethod,
-            new DescribeTableRequest
-            {
-                Path = path,
-                IncludeTableStats = settings.IncludeTableStats,
-                IncludePartitionStats = settings.IncludePartitionStats,
-                IncludeShardKeyBounds = settings.IncludeShardKeyBounds
-            },
-            settings
-        );
-
-        if (response.Operation.Status.IsNotSuccess())
-        {
-            throw YdbException.FromServer(response.Operation.Status, response.Operation.Issues);
-        }
-
-        return response.Operation.Result.Unpack<DescribeTableResult>();
-    }
-
     internal override async Task DeleteSession()
     {
         IsActive = false;
diff --git a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs
index e5f971b5..a8cec541 100644
--- a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs
+++ b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs
@@ -92,6 +92,8 @@ internal class MockSessionFactory : IPoolingSessionFactory
 
 internal class PoolingMockSession(PoolingSessionSource source) : IPoolingSession
 {
+    public IDriver Driver => throw new NotImplementedException();
+    
     public bool IsBroken => false;
 
     public void Close() => source.Return(this);
diff --git a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Stress.Loader/StressTestTank.cs b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Stress.Loader/StressTestTank.cs
index 109442c7..916a13ad 100644
--- a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Stress.Loader/StressTestTank.cs
+++ b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Stress.Loader/StressTestTank.cs
@@ -18,8 +18,11 @@ public StressTestTank(StressTestConfig config)
         _logger = loggerFactory.CreateLogger<StressTestTank>();
         _settings = new YdbConnectionStringBuilder(config.ConnectionString)
         {
-            CredentialsProvider =
-                config.SaFilePath != null ? new ServiceAccountProvider(config.SaFilePath, loggerFactory) : null
+            LoggerFactory = loggerFactory,
+            CredentialsProvider = config.SaFilePath != null
+                ? new ServiceAccountProvider(config.SaFilePath, loggerFactory)
+                : new MetadataProvider(loggerFactory),
+            ServerCertificates = YcCerts.GetYcServerCertificates()
         };
 
         ValidateConfig();
diff --git a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionSourceMockTests.cs b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionSourceMockTests.cs
index 1f22175d..6c67e223 100644
--- a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionSourceMockTests.cs
+++ b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionSourceMockTests.cs
@@ -39,21 +39,14 @@ public IPoolingSession NewSession(PoolingSessionSource source) =>
         new MockPoolingSession(source, Interlocked.Increment(ref _sessionNum));
 }
 
-internal class MockPoolingSession : IPoolingSession
+internal class MockPoolingSession(PoolingSessionSource source, int sessionNum) : IPoolingSession
 {
-    private readonly PoolingSessionSource _source;
-
-    internal string SessionId { get; }
-
-    public MockPoolingSession(PoolingSessionSource source, int sessionNum)
-    {
-        _source = source;
-        SessionId = $"session_{sessionNum}";
-    }
+    internal string SessionId { get; } = $"session_{sessionNum}";
 
+    public IDriver Driver => throw new NotImplementedException();
     public bool IsBroken { get; set; }
 
-    public void Close() => _source.Return(this);
+    public void Close() => source.Return(this);
 
     public Task Open(CancellationToken cancellationToken) => Task.CompletedTask;
 

From 73b6a8d56b95c56587462c698e71a84cc98338d3 Mon Sep 17 00:00:00 2001
From: KirillKurdyukov <kurdyukov-kir@ydb.tech>
Date: Tue, 22 Jul 2025 17:58:26 +0300
Subject: [PATCH 3/6] updating

---
 src/Ydb.Sdk/CHANGELOG.md                        |  3 +++
 src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs       |  4 ++--
 src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs   | 14 +++++++++-----
 .../src/Ado/Session/PoolingSessionSource.cs     |  5 -----
 src/Ydb.Sdk/src/Ado/YdbCommand.cs               |  1 -
 src/Ydb.Sdk/src/Services/Query/QueryClient.cs   |  3 ++-
 src/Ydb.Sdk/src/Services/Query/QueryTx.cs       | 11 +++++++----
 src/Ydb.Sdk/src/Services/Query/SessionPool.cs   | 17 ++++++++---------
 .../SessionSourceBenchmark.cs                   |  2 +-
 .../Session/PoolingSessionTests.cs              |  2 +-
 10 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/src/Ydb.Sdk/CHANGELOG.md b/src/Ydb.Sdk/CHANGELOG.md
index 9448d1d9..3eff72eb 100644
--- a/src/Ydb.Sdk/CHANGELOG.md
+++ b/src/Ydb.Sdk/CHANGELOG.md
@@ -1,3 +1,6 @@
+- Optimization: On BadSession, do not invoke the `DeleteSession()` method.
+- Canceling AttachStream after calling the `DeleteSession` method.
+- Fixed bug: fixed issue where session was not deleted (`ClientTransportTimeout`).
 - Fixed bug: Grpc.Core.StatusCode.Cancelled was mapped to server's Canceled status.
 - ADO.NET: PoolingSessionSource 2.0 based on Npgsql pooling algorithm.
 - Added new ADO.NET options:
diff --git a/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs b/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs
index bbe3ce0d..9669afb1 100644
--- a/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs
+++ b/src/Ydb.Sdk/src/Ado/Internal/SqlParser.cs
@@ -232,7 +232,7 @@ StringBuilder yql
                         return startToken; // rollback parse IN LIST
                     }
 
-                    yql.Append(listStartToken > startToken ? sql[startToken..listStartToken] : ' ');
+                    yql.Append(listStartToken > startToken ? sql[startToken .. listStartToken] : ' ');
                     var paramListName = sqlParamsBuilder.AddListPrimitiveParams(findNameParams);
                     yql.Append(paramListName);
 
@@ -273,7 +273,7 @@ private static (string Name, int NextToken) ParseNameParam(string sql, int curTo
             throw new YdbException($"Have empty name parameter, invalid SQL [position: {prevToken}]");
         }
 
-        return ($"${sql[prevToken..curToken]}", curToken);
+        return ($"${sql[prevToken .. curToken]}", curToken);
     }
 
     private static bool IsSqlIdentifierChar(this char c) => char.IsLetterOrDigit(c) || c == '_';
diff --git a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
index ed85d411..7d25cd4a 100644
--- a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
@@ -1,8 +1,3 @@
-// This file contains session pooling algorithms adapted from Npgsql
-// Original source: https://github.com/npgsql/npgsql
-// Copyright (c) 2002-2025, Npgsql
-// Licence https://github.com/npgsql/npgsql?tab=PostgreSQL-1-ov-file
-
 using Microsoft.Extensions.Logging;
 using Ydb.Query;
 using Ydb.Query.V1;
@@ -25,6 +20,7 @@ internal class PoolingSession : IPoolingSession
     private readonly CancellationTokenSource _attachStreamLifecycleCts = new();
 
     private volatile bool _isBroken = true;
+    private volatile bool _isBadSession = false;
 
     private readonly bool _disableServerBalancer;
 
@@ -105,6 +101,8 @@ public async Task RollbackTransaction(
 
     public void OnNotSuccessStatusCode(StatusCode statusCode)
     {
+        _isBadSession = _isBadSession || statusCode is StatusCode.BadSession;
+
         if (statusCode is
             StatusCode.BadSession or
             StatusCode.SessionBusy or
@@ -226,6 +224,12 @@ public async Task DeleteSession()
             _isBroken = true;
             _attachStreamLifecycleCts.CancelAfter(DeleteSessionTimeout);
 
+            if (_isBadSession)
+            {
+                return;
+            }
+
+            _isBadSession = true;
             var deleteSessionResponse = await Driver.UnaryCall(
                 QueryService.DeleteSessionMethod,
                 new DeleteSessionRequest { SessionId = SessionId },
diff --git a/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs b/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs
index b8880ca8..fc80f3a8 100644
--- a/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs
@@ -1,8 +1,3 @@
-// This file contains session pooling algorithms adapted from Npgsql
-// Original source: https://github.com/npgsql/npgsql
-// Copyright (c) 2002-2025, Npgsql
-// Licence https://github.com/npgsql/npgsql?tab=PostgreSQL-1-ov-file
-
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Threading.Channels;
diff --git a/src/Ydb.Sdk/src/Ado/YdbCommand.cs b/src/Ydb.Sdk/src/Ado/YdbCommand.cs
index ec49c0fa..2025991e 100644
--- a/src/Ydb.Sdk/src/Ado/YdbCommand.cs
+++ b/src/Ydb.Sdk/src/Ado/YdbCommand.cs
@@ -3,7 +3,6 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Text;
 using Ydb.Sdk.Ado.Internal;
-using Ydb.Sdk.Services.Query;
 using Ydb.Sdk.Value;
 
 namespace Ydb.Sdk.Ado;
diff --git a/src/Ydb.Sdk/src/Services/Query/QueryClient.cs b/src/Ydb.Sdk/src/Services/Query/QueryClient.cs
index 443d3b02..6820ba74 100644
--- a/src/Ydb.Sdk/src/Services/Query/QueryClient.cs
+++ b/src/Ydb.Sdk/src/Services/Query/QueryClient.cs
@@ -61,7 +61,8 @@ public Task<T> Stream<T>(string query, Func<ExecuteQueryStream, Task<T>> onStrea
         Dictionary<string, YdbValue>? parameters = null, TxMode txMode = TxMode.NoTx,
         ExecuteQuerySettings? settings = null) =>
         _sessionPool.ExecOnSession(async session => await onStream(new ExecuteQueryStream(
-            await session.ExecuteQuery(query, parameters, settings, txMode.TransactionControl())))
+            await session.ExecuteQuery(query, parameters ?? new Dictionary<string, YdbValue>(),
+                settings ?? new GrpcRequestSettings(), txMode.TransactionControl())))
         );
 
     public Task Stream(string query, Func<ExecuteQueryStream, Task> onStream,
diff --git a/src/Ydb.Sdk/src/Services/Query/QueryTx.cs b/src/Ydb.Sdk/src/Services/Query/QueryTx.cs
index c9aadf3e..15c72d37 100644
--- a/src/Ydb.Sdk/src/Services/Query/QueryTx.cs
+++ b/src/Ydb.Sdk/src/Services/Query/QueryTx.cs
@@ -28,10 +28,13 @@ internal QueryTx(Session session, TxMode txMode)
     }
 
     public async ValueTask<ExecuteQueryStream> Stream(string query, Dictionary<string, YdbValue>? parameters = null,
-        bool commit = false, ExecuteQuerySettings? settings = null) =>
-        new(
-            await _session.ExecuteQuery(query, parameters, settings, TxControl(commit)), txId => TxId = txId
-        );
+        bool commit = false, ExecuteQuerySettings? settings = null) => new(await _session.ExecuteQuery(
+            query,
+            parameters ?? new Dictionary<string, YdbValue>(),
+            settings ?? new GrpcRequestSettings(),
+            TxControl(commit)
+        ), txId => TxId = txId
+    );
 
     public async Task<IReadOnlyList<Value.ResultSet.Row>> ReadAllRows(string query,
         Dictionary<string, YdbValue>? parameters = null, bool commit = false, ExecuteQuerySettings? settings = null)
diff --git a/src/Ydb.Sdk/src/Services/Query/SessionPool.cs b/src/Ydb.Sdk/src/Services/Query/SessionPool.cs
index d843fae0..915f69c3 100644
--- a/src/Ydb.Sdk/src/Services/Query/SessionPool.cs
+++ b/src/Ydb.Sdk/src/Services/Query/SessionPool.cs
@@ -18,15 +18,14 @@ internal sealed class SessionPool : SessionPool<Session>, IAsyncDisposable
 {
     private static readonly CreateSessionRequest CreateSessionRequest = new();
 
+    private readonly IDriver _driver;
     private readonly bool _disposingDriver;
     private readonly ILogger<Session> _loggerSession;
 
-    internal readonly IDriver Driver;
-
     internal SessionPool(IDriver driver, SessionPoolConfig sessionPoolConfig)
         : base(driver.LoggerFactory.CreateLogger<SessionPool>(), sessionPoolConfig)
     {
-        Driver = driver;
+        _driver = driver;
         _disposingDriver = sessionPoolConfig.DisposeDriver;
         _loggerSession = driver.LoggerFactory.CreateLogger<Session>();
     }
@@ -45,7 +44,7 @@ protected override async Task<Session> CreateSession(
             requestSettings.ClientCapabilities.Add("session-balancer");
         }
 
-        var response = await Driver.UnaryCall(
+        var response = await _driver.UnaryCall(
             QueryService.CreateSessionMethod,
             CreateSessionRequest,
             requestSettings
@@ -58,13 +57,13 @@ protected override async Task<Session> CreateSession(
         var sessionId = response.SessionId;
         var nodeId = response.NodeId;
 
-        var session = new Session(Driver, this, sessionId, nodeId, _loggerSession);
+        var session = new Session(_driver, this, sessionId, nodeId, _loggerSession);
 
         _ = Task.Run(async () =>
         {
             try
             {
-                using var stream = await Driver.ServerStreamCall(
+                using var stream = await _driver.ServerStreamCall(
                     QueryService.AttachSessionMethod,
                     new AttachSessionRequest { SessionId = sessionId },
                     new GrpcRequestSettings { NodeId = nodeId }
@@ -137,7 +136,7 @@ protected override async Task<Session> CreateSession(
         return session;
     }
 
-    protected override ValueTask DisposeDriver() => _disposingDriver ? Driver.DisposeAsync() : default;
+    protected override ValueTask DisposeDriver() => _disposingDriver ? _driver.DisposeAsync() : default;
 }
 
 internal class Session : SessionBase<Session>, ISession
@@ -156,8 +155,8 @@ ILogger<Session> logger
     public IDriver Driver { get; }
 
     public ValueTask<IServerStream<ExecuteQueryResponsePart>> ExecuteQuery(
-        string query, 
-        Dictionary<string, YdbValue> parameters, 
+        string query,
+        Dictionary<string, YdbValue> parameters,
         GrpcRequestSettings settings,
         TransactionControl? txControl)
     {
diff --git a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs
index a8cec541..20ce8cb7 100644
--- a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs
+++ b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Benchmarks/SessionSourceBenchmark.cs
@@ -93,7 +93,7 @@ internal class MockSessionFactory : IPoolingSessionFactory
 internal class PoolingMockSession(PoolingSessionSource source) : IPoolingSession
 {
     public IDriver Driver => throw new NotImplementedException();
-    
+
     public bool IsBroken => false;
 
     public void Close() => source.Return(this);
diff --git a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs
index 66b936f7..52b38ead 100644
--- a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs
+++ b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs
@@ -269,7 +269,7 @@ private TaskCompletionSource<bool> SetupAttachStream()
     {
         var tcsSecondMoveAttachStream = new TaskCompletionSource<bool>();
 
-        _mockAttachStream.SetupSequence(attachStream => attachStream.MoveNextAsync(CancellationToken.None))
+        _mockAttachStream.SetupSequence(attachStream => attachStream.MoveNextAsync(It.IsAny<CancellationToken>()))
             .ReturnsAsync(true)
             .Returns(new ValueTask<bool>(tcsSecondMoveAttachStream.Task));
         _mockAttachStream.SetupSequence(attachStream => attachStream.Current)

From 80a1655b7613c92e95681406e518df7498c88b31 Mon Sep 17 00:00:00 2001
From: KirillKurdyukov <kurdyukov-kir@ydb.tech>
Date: Tue, 22 Jul 2025 18:14:10 +0300
Subject: [PATCH 4/6] fix test

---
 .../test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs
index 52b38ead..c59fc739 100644
--- a/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs
+++ b/src/Ydb.Sdk/test/Ydb.Sdk.Ado.Tests/Session/PoolingSessionTests.cs
@@ -47,13 +47,7 @@ public async Task OnNotSuccessStatusCode_WhenStatusCodeIsNotSuccess_UpdateIsBrok
         bool isError)
     {
         SetupSuccessCreateSession();
-        var tcsSecondMoveAttachStream = new TaskCompletionSource<bool>();
-
-        _mockAttachStream.SetupSequence(attachStream => attachStream.MoveNextAsync(CancellationToken.None))
-            .ReturnsAsync(true)
-            .Returns(new ValueTask<bool>(tcsSecondMoveAttachStream.Task));
-        _mockAttachStream.SetupSequence(attachStream => attachStream.Current)
-            .Returns(new SessionState { Status = StatusIds.Types.StatusCode.Success });
+        var tcsSecondMoveAttachStream = SetupAttachStream();
         var session = _poolingSessionFactory.NewSession(_poolingSessionSource);
         Assert.True(session.IsBroken);
         await session.Open(CancellationToken.None);

From b3aab22e712776dc24f042909e0f8f136329243a Mon Sep 17 00:00:00 2001
From: KirillKurdyukov <kurdyukov-kir@ydb.tech>
Date: Tue, 22 Jul 2025 18:19:48 +0300
Subject: [PATCH 5/6] fix

---
 src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
index 7d25cd4a..9fc99258 100644
--- a/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/PoolingSession.cs
@@ -20,7 +20,7 @@ internal class PoolingSession : IPoolingSession
     private readonly CancellationTokenSource _attachStreamLifecycleCts = new();
 
     private volatile bool _isBroken = true;
-    private volatile bool _isBadSession = false;
+    private volatile bool _isBadSession;
 
     private readonly bool _disableServerBalancer;
 

From 55ba0af20da96e417d9c466292b5511e98322f54 Mon Sep 17 00:00:00 2001
From: KirillKurdyukov <kurdyukov-kir@ydb.tech>
Date: Tue, 22 Jul 2025 18:35:24 +0300
Subject: [PATCH 6/6] fix

---
 .../src/Ado/Session/PoolingSessionSource.cs   | 53 ++++++++-----------
 src/Ydb.Sdk/src/Ado/YdbConnection.cs          | 14 ++++-
 2 files changed, 33 insertions(+), 34 deletions(-)

diff --git a/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs b/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs
index fc80f3a8..05c487ff 100644
--- a/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs
+++ b/src/Ydb.Sdk/src/Ado/Session/PoolingSessionSource.cs
@@ -87,45 +87,34 @@ private async ValueTask<IPoolingSession> RentAsync(CancellationToken cancellatio
 
         var finalToken = ctsGetSession.Token;
 
-        try
+        var session = await OpenNewSession(finalToken).ConfigureAwait(false);
+        if (session != null)
+            return session;
+
+        while (true)
         {
-            var session = await OpenNewSession(finalToken).ConfigureAwait(false);
-            if (session != null)
-                return session;
+            session = await _idleSessionReader.ReadAsync(finalToken).ConfigureAwait(false);
 
-            while (true)
+            if (CheckIdleSession(session))
             {
-                session = await _idleSessionReader.ReadAsync(finalToken).ConfigureAwait(false);
-
-                if (CheckIdleSession(session))
-                {
-                    return session;
-                }
+                return session;
+            }
 
-                // If we're here, our waiting attempt on the idle session channel was released with a null
-                // (or bad session), or we're in sync mode. Check again if a new idle session has appeared since we last checked.
-                if (TryGetIdleSession(out session))
-                {
-                    return session;
-                }
+            // If we're here, our waiting attempt on the idle session channel was released with a null
+            // (or bad session), or we're in sync mode. Check again if a new idle session has appeared since we last checked.
+            if (TryGetIdleSession(out session))
+            {
+                return session;
+            }
 
-                // We might have closed a session in the meantime and no longer be at max capacity
-                // so try to open a new session and if that fails, loop again.
-                session = await OpenNewSession(finalToken).ConfigureAwait(false);
-                if (session != null)
-                {
-                    return session;
-                }
+            // We might have closed a session in the meantime and no longer be at max capacity
+            // so try to open a new session and if that fails, loop again.
+            session = await OpenNewSession(finalToken).ConfigureAwait(false);
+            if (session != null)
+            {
+                return session;
             }
         }
-        catch (OperationCanceledException e)
-        {
-            throw new YdbException(StatusCode.Cancelled,
-                $"The connection pool has been exhausted, either raise 'MaxSessionPool' " +
-                $"(currently {_maxSessionSize}) or 'CreateSessionTimeout' " +
-                $"(currently {_createSessionTimeout} seconds) in your connection string.", e
-            );
-        }
     }
 
     private async ValueTask<IPoolingSession?> OpenNewSession(CancellationToken cancellationToken)
diff --git a/src/Ydb.Sdk/src/Ado/YdbConnection.cs b/src/Ydb.Sdk/src/Ado/YdbConnection.cs
index ce2e2c43..a240e4bc 100644
--- a/src/Ydb.Sdk/src/Ado/YdbConnection.cs
+++ b/src/Ydb.Sdk/src/Ado/YdbConnection.cs
@@ -92,8 +92,18 @@ public override void ChangeDatabase(string databaseName)
     public override async Task OpenAsync(CancellationToken cancellationToken)
     {
         ThrowIfConnectionOpen();
-
-        Session = await PoolManager.GetSession(ConnectionStringBuilder, cancellationToken);
+        try
+        {
+            Session = await PoolManager.GetSession(ConnectionStringBuilder, cancellationToken);
+        }
+        catch (OperationCanceledException e)
+        {
+            throw new YdbException(StatusCode.Cancelled,
+                $"The connection pool has been exhausted, either raise 'MaxSessionPool' " +
+                $"(currently {ConnectionStringBuilder.MaxSessionPool}) or 'CreateSessionTimeout' " +
+                $"(currently {ConnectionStringBuilder.CreateSessionTimeout} seconds) in your connection string.", e
+            );
+        }
 
         OnStateChange(ClosedToOpenEventArgs);