Exception: 'Pooling must be on to use multiplexing', even though Pooling is explicitly on.

[akilin]

Steps to reproduce

https://github.com/akilin/demos/tree/master/pg-multiplexing-pooling

run commands:

git clone https://github.com/akilin/demos
cd pg-multiplexing-pooling
docker-compose up -d
dotnet run

The issue

Hi, I wanted to try out Multiplexing that was released as part of 5.0.
Once I've added Multiplexing = true to my ConnectionStringBuilder - app started erroring when trying to Delete/Migrate a database.
Error message says that Pooling must be on to use multiplexing.. but pooling is on by default as far as I can tell.
I tried explicitly setting Pooling = true in code - but I am still getting same results.

Exception message: Pooling must be on to use multiplexing
Stack trace: 
   at Npgsql.NpgsqlConnectionStringBuilder.Validate()
   at Npgsql.NpgsqlConnection.GetPoolAndSettings()
   at Npgsql.NpgsqlConnection.set_ConnectionString(String value)
   at Npgsql.NpgsqlConnection..ctor(String connectionString)
   at Npgsql.NpgsqlConnection.CloneWith(String connectionString)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlDatabaseCreator.Exists()
   at Microsoft.EntityFrameworkCore.Storage.RelationalDatabaseCreator.EnsureDeleted()
   at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.EnsureDeleted()
   at pg_multiplexing_pooling.Program.Main(String[] args) in C:\git\demos\pg-multiplexing-pooling\Program.cs:line 12

Further technical details

Npgsql version: 5.0.0
PostgreSQL version: latest docker image
Operating system: Windows 10

The issue seems to be happening because of next line:
https://github.com/npgsql/efcore.pg/blob/main/src/EFCore.PG/Storage/Internal/NpgsqlDatabaseCreator.cs#L136

[akilin]

I would like to take a stab at the issue.. I assume the fix will be addition of Multiplexing = false inside Exists/ExistsAsync methods.

[roji]

Thanks for this fix @akilin!

It's nice to see people using multiplexing - I should really get around to properly documenting the feature. I'd be very interested in hearing your experience with it.