NpgsqlException - Exception while reading from stream

I am getting random error messages in my application log with the following stack trace. Most of the time everything is working well. I get about 10 errors and log messages like this a day in the production system. How do I figure out what is going on?

The issue

ERROR [18] 
 Npgsql.NpgsqlException (0x80004005): Exception while reading from stream ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
    at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
    --- End of inner exception stack trace ---
    at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
    at Npgsql.NpgsqlReadBuffer.<>c__DisplayClass31_0.<<Ensure>g__EnsureLong|0>d.MoveNext()
    at Npgsql.NpgsqlReadBuffer.<>c__DisplayClass31_0.<<Ensure>g__EnsureLong|0>d.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at Npgsql.NpgsqlConnector.<>c__DisplayClass161_0.<<ReadMessage>g__ReadMessageLong|0>d.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at Npgsql.NpgsqlConnector.<>c__DisplayClass161_0.<<ReadMessage>g__ReadMessageLong|0>d.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at Npgsql.NpgsqlDataReader.NextResult(Boolean async, Boolean isConsuming)
    at Npgsql.NpgsqlDataReader.NextResult()
    at Npgsql.NpgsqlCommand.ExecuteDbDataReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
    at Npgsql.NpgsqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
    at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader(CommandBehavior behavior)
    at Dapper.SqlMapper.ExecuteReaderWithFlagsFallback(IDbCommand cmd, Boolean wasClosed, CommandBehavior behavior) in C:\projects\dapper\Dapper\SqlMapper.cs:line 1051
    at Dapper.SqlMapper.QueryImpl[T](IDbConnection cnn, CommandDefinition command, Type effectiveType)+MoveNext() in C:\projects\dapper\Dapper\SqlMapper.cs:line 1079
    at System.Collections.Generic.List`1.AddEnumerable(IEnumerable`1 enumerable)
    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
    at Dapper.SqlMapper.Query[T](IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Boolean buffered, Nullable`1 commandTimeout, Nullable`1 commandType) in C:\projects\dapper\Dapper\SqlMapper.cs:line 721
    at Dapper.FastCrud.SqlStatements.GenericSqlStatements`1.BatchSelect(IDbConnection connection, AggregatedSqlStatementOptions`1 statementOptions) in D:\a\1\s\Dapper.FastCrud\SqlStatements\GenericSqlStatements.cs:line 297
    at XXX.Core.Data.SqlRepository`1.FirstOrDefault(String where, Object param, String order)
    at XXXXX.App.Worker.Tasks.XXX.Process() in C:\Dropbox\dev\Src\shop\XXX\Tasks\ShopifyWebhookTask.cs:line 13
    at XXX.App.Worker.TaskBase`1.ProcessMessage(String message) in C:\Dropbox\dev\Src\shop\XXX\TaskBase.cs:line 30
    at Shop.Core.Common.Queue.BaseTaskProcessor`1.Process(QueueMessage message) in C:\Dropbox\dev\Src\shop\XXX\Queue\BaseTaskProcessor.cs:line 38

Exception message:
Stack trace:

Npgsql version: 4.0.10 PostgreSQL version: 10.10 Operating system: Azure Windows Function + Azure Managed PostgresSql.

[stvoidmain]

I’m using 4.1.2 now and still getting the same behaviour, gonna try to reproduce it locally and debug.

[roji]

Guys, the error message is saying that PostgreSQL closed the connection for some reason. In these cases, the PostgreSQL log almost always contains a message that provides insight into why that happened - please post those messages here and we can investigate further, otherwise there’s no enough information.