Postgresql: No connection could be made because the target machine actively refused it - windows

Question

Running Postgresql 9.5 on a windows server 2012 R2 in Azure
While running some loadtests on my application, I get errors on not being able to connect to the postgres server. In the logs of postgres I get the following message:
could not receive data from client: No connection could be made
because the target machine actively refused it.
This only happens when the loadtest goes to the next scenario, hitting a different part of the code. So new connections to the database are required. But after 10-20 seconds the rest of the scenario works flawlessly without hitting any other hiccups. So the problem seems to be the tcp connections. (My code retries a couple of times but it is not feasible to let it retry for 20 seconds)
I'm using the following settings in the config files
postgresql.conf
listen_addresses = '*'
max_connections = 500
shared_buffers = 1024MB
temp_buffers = 2MB
work_mem = 2MB
maintenance_work_mem = 128MB
pg_hba.conf
host all all 0.0.0.0/0 trust
host all all ::/0 trust
I know, I know.. It is not save to accept connections from everyone, but this is just for testing purposes and to make sure these settings are not blocking any connection. So this answer is void
I've been monitoring the number of connection on the server and under the load it is stable at 75. Postgres is using around 350mb of RAM. So given the config and the vm specs (7gb ram) there should be plenty of space to create more connections. However when the next scenario is spinning up the number of connections does not increase, it stays level and starts giving these log messages about no connection could be made.
What could be the problem here?

Answer 1

It does sound like this isn't really a Postgres problem (hence no changes in DB stats you're checking), rather that the traffic is being stopped by the server. Possibly because traffic on that port is saturated while handling your load testing queries?
It doesn't sound like you're hitting any of the Azure resource limits (including the database limits if that applies to your setup?), but without more detail on your load tests it's hard to say exactly what is needed.
Solutions from around the web and other SO answers suggest:
Disable TCP autotuning and tweak the TCP/IP registry keys on the server, e.g. set TcpAckFrequency - see this article for details
Make TCP setting adjustments (like WinsockListenBacklog) - which may be affected by whether connection pooling is in use or not - see this MS support article, which is for SQL Server 2005 but has some great tips on troubleshooting rejected TCP/IP connections (using Network Monitor, but applies to newer tools)
Faster request processing if you have enough control of the server - source
Disabling network proxying (in your load testing app): <defaultProxy> <proxy usesystemdefault="False"/> </defaultProxy> - source

Answer 2

Most possible reason is a Firewall/Anti-virus:
Software/Personal Firewall Settings
Multiple Software/Personal Firewalls
Anti-virus Software
LSP Layer
(Virtual) Router Firmware
Does your current Azure infrastructure contain Firewall or Anti-virus ?
Additionally on doing some additional searches, it looks like this is a standard Windows "connection refused" message, which suggests that PostgreSQL is trying to connect to something and being refused.
Also possible that one network element in your network - assuming that you are still connected to the server - will delay or drop somes DB login/authentication network packets (considered for example as a fake auth.replay) ...
You may also use a packet analyzer (like Wireshark) to record/inspect network flow when the error appear.
Regards

Answer 3

I was facing the same issue in my AspNet core application while I was trying to connect the Postgresql from my application. The error was thrown in the Program.cs file when I was calling the Migrate function.
public static void Main(string[] args) {
try {
var host = BuildWebHost(args);
using(var scope = host.Services.CreateScope()) {
// Migrate once after app is started.
scope.ServiceProvider.GetService <MyDatabaseContext>().Migrate();
}
host.Run();
}
catch(Exception e) {
//NLog: catch setup errors
_logger ? .Error(e, "Stopped program because of exception: ");
throw;
}
}
To fix this problem I did the following steps.
Check whether the Postgresql service is running by going to the services.msc
Tried to login to the pgAdmin with the user and password I provided in the database context
Everything was file, and as you know that 5432 is the default port of Postgresql and somehow I was using a different port in my application connection string, changing it to 5432 fixed this issue for me.
"ConnectionString": "User Id=postgres;Password=mypwd;Host=localhost;Port=5432;Database=mydb;"

Answer 4

I came across a similar issue whilst trying to beast my api, where I was seeing Npgsql.NpgsqlException No connection could be made because the target machine actively refused it..
However my issue was was down to the fact that I was re-creating my NpgsqlConnection for each query rather than re-using and keeping it alive.