dbt --single-threaded rpc does not work

[drewbanin]

Describe the bug

The dbt executable supports a flag called --single-threaded which is intended to bypass multithreading when building nodes (eg. models, seeds, whatever). The --single-threaded argument previously worked with the dbt rpc command, but it appears that there is now a regression!

Steps To Reproduce

Run the rpc server in single-threaded mode:

dbt --single-threaded rpc

Run a query against the server (this one does select 1 as id):

curl --location --request POST 'http://localhost:8580/jsonrpc' --header 'Content-Type: application/json' --data-raw '{
	"jsonrpc": "2.0",
	"method": "run_sql",
	"id": "123",
	"params": {
		"sql": "c2VsZWN0IDEgYXMgaWQ=",
        "name": "my_query"
	}
}'

This returns the following error:

{
    "error": {
        "code": -32000,
        "message": "Server Error",
        "data": {
            "type": "Exception",
            "message": "'Manifest' object has no attribute 'root_project'",
            "tags": null,
            "logs": [
                {
                    "timestamp": "2021-03-30T21:35:40.781048Z",
                    "message": "Acquiring new postgres connection \"rpc.debug.my_query\".",
                    "channel": "dbt",
                    "level": 10,
                    "levelname": "DEBUG",
                    "thread_name": "MainThread",
                    "process": 76144,
                    "extra": {
                        "request_id": "123",
                        "method": "run_sql",
                        "context": "request",
                        "addr": "127.0.0.1",
                        "http_method": "POST",
                        "run_state": "internal"
                    }
                },
                {
                    "timestamp": "2021-03-30T21:35:40.791030Z",
                    "message": "uncaught python exception",
                    "channel": "dbt",
                    "level": 14,
                    "levelname": "ERROR",
                    "thread_name": "MainThread",
                    "process": 76144,
                    "extra": {
                        "request_id": "123",
                        "method": "run_sql",
                        "context": "request",
                        "addr": "127.0.0.1",
                        "http_method": "POST",
                        "run_state": "internal"
                    },
                    "exc_info": "Traceback (most recent call last):\n  File \"/Users/drew/fishtown/dbt/core/dbt/rpc/task_handler.py\", line 94, in task_exec\n    result = self.task.handle_request()\n  File \"/Users/drew/fishtown/dbt/core/dbt/task/rpc/sql_commands.py\", line 162, in handle_request\n    node = self._get_exec_node()\n  File \"/Users/drew/fishtown/dbt/core/dbt/task/rpc/sql_commands.py\", line 123, in _get_exec_node\n    add_new_refs(\n  File \"/Users/drew/fishtown/dbt/core/dbt/task/rpc/sql_commands.py\", line 38, in add_new_refs\n    manifest = manifest.deepcopy()\n  File \"/Users/drew/fishtown/dbt/core/dbt/contracts/graph/manifest.py\", line 729, in deepcopy\n    selectors=self.root_project.manifest_selectors,\nAttributeError: 'Manifest' object has no attribute 'root_project'"
                }
            ]
        }
    },
    "id": "123",
    "jsonrpc": "2.0"
}

Expected behavior

I expect the request to succeed and return a successful response. I also expect the --single-threaded command to block until the query returns, then return a complete success response. This is (if I am recalling correctly) the intended behavior of the --single-threaded flag. This is a different behavior than the default which is to return a "task_id" immediately which can be polled for a response.

Screenshots and log output

Attached above

System information

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: ____________)

The output of dbt --version:

0.19.0

Using current develop branch at commit 17e57f1e0b3

The operating system you're using: macOS

The output of python --version: 3.8.6

Additional context

Should this be a command-line flag (--single-threaded?) or should it be an option in the RPC request method like sync: true? Just a thought :)

[gshank]

This is a regression due to changes for #2693. We don't have any test cases for the rpc single threaded option, and that's the only place that Manifest.deepcopy code is called.

[gshank]

This was fixed a few months back.