fastapi + aiomysql 连接池在 10 次调用后卡住

Question

为什么aiomysql连接池在调用N次后卡住了？（N是maxsize个连接数，试过默认N=10和N=3）

我认为获取的连接会在 async with 退出时自动关闭。

这是要重现的最小脚本：

from fastapi import FastAPI
import aiomysql
import secret

app = FastAPI()

@app.on_event("startup")
async def _startup():
    app.state.pool = await aiomysql.create_pool(host=secret.DB_URL, port=3306, user=secret.DB_USERNAME, password=secret.DB_PASSWORD, db=secret.DB_DATABASE)
    print("startup done")

async def _get_query_with_pool(pool):
    async with await pool.acquire() as conn:
        async with conn.cursor(aiomysql.DictCursor) as cur:
            await cur.execute("SELECT 1")
            return await cur.fetchall()

@app.get("/v1/get_data")
async def _get_data():
    return await _get_query_with_pool(app.state.pool)


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app, host="0.0.0.0", port=8000)

Answer 1

原来罪魁祸首是 pool.acquire()

之前的额外等待

async def _get_query_with_pool(pool):
    async with await pool.acquire() as conn:
        async with conn.cursor(aiomysql.DictCursor) as cur:
            await cur.execute("SELECT 1")
            return await cur.fetchall()

去掉pool.acquire()前的多余等待，所以：

async def _get_query_with_pool(pool):
    async with pool.acquire() as conn:
        async with conn.cursor(aiomysql.DictCursor) as cur:
            await cur.execute("SELECT 1")
            return await cur.fetchall()

现在连接成功了

2021 年第四季度更新：

事实证明连接池不值得。连接池可能导致 mysql8 alter table 永远锁定。只需打开和关闭数据库连接。

fastapi + aiomysql 连接池在 10 次调用后卡住

fastapi + aiomysql connection pool stuck after 10 calls

python

python-asyncio

aiopg

fastapi

aio-mysql