When aiotools num_worker set as many as cpu cores, dead with error.

[FuZer]

If I specify num_worker as the number of cores as mentioned in the title, an error occurs.
So I specify 20 worker. any other way to solve this?

$ grep -c processor /proc/cpuinfo
40

ERROR aiotools.server [Process-7] Worker 7: Error during initialization
Traceback (most recent call last):
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiotools/server.py", line 56, in _worker_main
    loop.run_until_complete(ctx.__aenter__())
  File "uvloop/loop.pyx", line 1203, in uvloop.loop.Loop.run_until_complete (uvloop/loop.c:25636)
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiotools/context.py", line 78, in __aenter__
    return (await self._agen.__anext__())
  File "/home/ubuntu/backend.ai-manager/ai/backend/gateway/server.py", line 284, in server_main
    await gw_init(app)
  File "/home/ubuntu/backend.ai-manager/ai/backend/gateway/server.py", line 188, in gw_init
    timeout=30, pool_recycle=30,
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/utils.py", line 70, in __await__
    resp = yield from self._coro
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/sa/engine.py", line 70, in _create_engine
    pool_recycle=pool_recycle, **kwargs)
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/utils.py", line 65, in __iter__
    resp = yield from self._coro
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/pool.py", line 47, in _create_pool
    yield from pool._fill_free_pool(False)
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/pool.py", line 209, in _fill_free_pool
    **self._conn_kwargs)
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/utils.py", line 65, in __iter__
    resp = yield from self._coro
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/connection.py", line 74, in _connect
    yield from conn._poll(waiter, timeout)
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/connection.py", line2018-03-30 14:02:57 INFO ai.backend.gateway.server [Process-6] shutting down...
 238, in _poll
    yield from asyncio.wait_for(self._waiter, timeout, loop=self._loop)
  File "/home/ubuntu/.pyenv/versions/3.6.4/lib/python3.6/asyncio/tasks.py", line 358, in wait_for
    return fut.result()
  File "/home/ubuntu/.pyenv/versions/venv-manager/lib/python3.6/site-packages/aiopg/connection.py", line 135, in _ready
    state = self._conn.poll()
psycopg2.OperationalError: FATAL:  sorry, too many clients already

[achimnol]

I'll look into it!

[achimnol]

The number of workers in the Backend.AI gateway is not related to the performance of your Backend.AI user-code execution. It mainly affects the API (HTTP request) processing throughput.

Therefere it is safe to have low numbers for private setups where the concurrent client connections are far less than hundreds or thousands. Even a single thread setup can handle hundreds of concurrent HTTP requests without hassles. (In Backend.AI, the main performance-limiting factor is the latency of Docker APIs in the agents.)

So I'm going to add a patch so that you can customize the number of gateway processes using a CLI argument while its default is set to a small number (at most 4).

[achimnol]

As there are no more responses after I have provided the patch, closing the issue.
Please reopen or open another issue if you have further problems.