Asyncpg.pool creates more connections than its max_size

• asyncpg version:0.29.0
• PostgreSQL version: "PostgreSQL 16.0 (Debian 16.0-1.pgdg120+1) on aarch64-unknown-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit"
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: Nope, using Dockerized container
• Python version: 3.11.5
• Platform: MacBook-Air Darwin Kernel Version 21.1.0: Wed Oct 13 17:33:24 PDT 2021; root:xnu-8019.41.5~1/RELEASE_ARM64_T8101 arm64
• Do you use pgbouncer?: Nope
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: n/a
• Can the issue be reproduced under both asyncio and
  uvloop?:Nope

I have a singleton for a Database entity, which is then used to write some primitive data. When I run the write function 1000 times concurrently using asyncio.gather(), the database reports that there is more connections than the max_size of the asyncpg.pool. For example, when I was testing there were 857 active db connections, but only 62 active pool connections. No other clients/operations were running during the test. When I use uvloop to do the same thing, it just crashes with ConnectionResetError: [Errno 54] Connection reset by peer if I try to run more tasks than the size of the pool.

Is this a normal pool behavior?

I use code below (the write function is simplified though):

The database code:

  class Database:
      _instance = None
      _pool = None
      db_params = { 
                  'host': os.getenv('DATABASE_HOST'),
                  'port': os.getenv('DATABASE_PORT'),
                  'database': os.getenv('DATABASE_NAME'),
                  'user': os.getenv('DATABASE_USER'),
                  'password': os.getenv('DATABASE_PASSWORD')
              }
  
      def __new__(cls, *args, **kwargs):
          if cls._instance is None:
              cls._instance = super(Database, cls).__new__(cls)
              #print(cls._instance)
          return cls._instance
  
      @classmethod
      async def get_pool(cls):
          if cls._pool is None:
              cls._pool = await asyncpg.create_pool(**cls.db_params, min_size=1, max_size=150)
              #print(cls._pool)
          return cls._pool

    @classmethod
    async def write(cls, result):
            pool = await cls.get_pool()
            try:
                    async with pool.acquire() as connection:
                        result = await connection.execute('''
                            INSERT INTO tables.results(
                                result
                            ) VALUES($1)
                        ''', result)
                        return
            except Exception as e:
                raise e

The demo write code

async def fake_result(i):
    print(f'generating fake result {i}')
    await db.write(i)
    return

async def run_functions_concurrently():
   tasks = [fake_result(i) for i in range(1000)]
   await asyncio.gather(*tasks)

def main():
    asyncio.run(run_functions_concurrently())

if __name__ == "__main__":
    main()

Bắt đầu với asyncpg.create_pool, pool.acquire và đường dẫn ghi được hiển thị trong issue. Tái hiện run_functions_concurrently với 1000 task được gather và so sánh số kết nối đang hoạt động của PostgreSQL với max_size là 150 của pool. Hoàn thành nghĩa là xác định liệu số lượng kết nối có đúng như mong đợi hay không, đồng thời ghi lại hoặc sửa hành vi quan sát được.