0x80131904 dotnet resource_error ai_generated true

Microsoft.Data.SqlClient.SqlException (0x80131904): Connection 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.

ID: dotnet/ef-core-connection-timeout

Also available as: JSON · Markdown · 中文
85%Fix Rate
85%Confidence
1Evidence
2023-06-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
net6.0 active — — —
net7.0 active — — —
net8.0 active — — —
net9.0 active — — —

Root Cause

The connection pool is exhausted because connections are not being closed/disposed properly, or the pool size is too small for the concurrent load.

generic

中文

连接池耗尽，因为连接未正确关闭/释放，或者池大小对于并发负载来说太小。

Official Documentation

https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/sql-server-connection-pooling

Workarounds

  1. 90% success Ensure all DbContext instances are properly disposed by using 'using' blocks or dependency injection with AddDbContext and scoped lifetime. Example: 'using (var context = new MyDbContext()) { ... }' or services.AddDbContext<MyDbContext>(options => options.UseSqlServer(connectionString), ServiceLifetime.Scoped) 
    Ensure all DbContext instances are properly disposed by using 'using' blocks or dependency injection with AddDbContext and scoped lifetime. Example: 'using (var context = new MyDbContext()) { ... }' or services.AddDbContext<MyDbContext>(options => options.UseSqlServer(connectionString), ServiceLifetime.Scoped)
  2. 80% success Increase connection pool size and add connection leak detection. Set 'Max Pool Size=200; Connection Lifetime=300' in the connection string, and enable 'Pooling=True' with 'Load Balance Timeout=30'. Also monitor with 'SELECT * FROM sys.dm_exec_sessions' to identify orphaned connections. 
    Increase connection pool size and add connection leak detection. Set 'Max Pool Size=200; Connection Lifetime=300' in the connection string, and enable 'Pooling=True' with 'Load Balance Timeout=30'. Also monitor with 'SELECT * FROM sys.dm_exec_sessions' to identify orphaned connections.
  3. 85% success Use 'using var connection = new SqlConnection(connectionString);' and wrap in try-finally or use 'await using' for async operations. For EF Core, ensure 'context.Database.CloseConnection()' is called in long-running operations. 
    Use 'using var connection = new SqlConnection(connectionString);' and wrap in try-finally or use 'await using' for async operations. For EF Core, ensure 'context.Database.CloseConnection()' is called in long-running operations.

中文步骤

  1. Ensure all DbContext instances are properly disposed by using 'using' blocks or dependency injection with AddDbContext and scoped lifetime. Example: 'using (var context = new MyDbContext()) { ... }' or services.AddDbContext<MyDbContext>(options => options.UseSqlServer(connectionString), ServiceLifetime.Scoped)
  2. Increase connection pool size and add connection leak detection. Set 'Max Pool Size=200; Connection Lifetime=300' in the connection string, and enable 'Pooling=True' with 'Load Balance Timeout=30'. Also monitor with 'SELECT * FROM sys.dm_exec_sessions' to identify orphaned connections.
  3. Use 'using var connection = new SqlConnection(connectionString);' and wrap in try-finally or use 'await using' for async operations. For EF Core, ensure 'context.Database.CloseConnection()' is called in long-running operations.

Dead Ends

Common approaches that don't work:

  1. Increasing Max Pool Size in connection string to a very high value (e.g., 1000) 85% fail

    This only masks the underlying issue of connection leaks; the pool will eventually exhaust again under higher load.

  2. Restarting the application or IIS pool to clear connections 90% fail

    Temporary fix; connections will leak again once the app runs, as the root cause (missing Dispose) persists.

  3. Disabling connection pooling entirely (Pooling=false) 95% fail

    Severely impacts performance by creating a new connection for every request, leading to slower response times and potential socket exhaustion.