Memory leak with Pool usage

• asyncpg version: 0.27
• PostgreSQL version: 14
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: no
• Python version: 3.8, 3.10 and 3.11
• Platform: docker images python:3.x-slim-buster
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• Can the issue be reproduced under both asyncio and
  uvloop?: only asyncio

When we use a Pool, the memory usage of our process keeps increasing slowly with the number of queries. After 1000 queries, it is ~10MB and this increases with the number of queries executed on connections acquired from the pool. This remains after the max_inactive_connection_lifetime has passed with no activity, with explicit garbage collection and even after we close the pool. We can reproduce this with a psutil measurement and observe it in production. When we replace the usage of Pool with our own creation/cleanup of asynpg Connections, the issue dissapears.

Pool created with the following arguments:

asyncpg.create_pool(
    max_inactive_connection_lifetime=300,
    command_timeout=30,
    min_size=0,
    max_size=5
)

从 asyncpg.create_pool 入口点开始，使用报告中的池参数，并通过所描述的 psutil 测量方法复现内存逐渐增加的现象。将池化连接与直接的 asyncpg 连接进行比较，包括在 max_inactive_connection_lifetime 之后、显式垃圾回收之后以及关闭池之后的情况。当复现不再显示与查询数量相关的增长时，即表示完成。