fastapi + aiomysql 连接池在 10 次调用后卡住

Posted 2023-03-30

【中文标题】fastapi + aiomysql 连接池在 10 次调用后卡住

【英文标题】：fastapi + aiomysql connection pool stuck after 10 calls

【发布时间】：2021-02-16 10:30:16

【问题描述】：

为什么aiomysql连接池在N次调用后卡住了？ （N是maxsize的连接数。尝试了默认的N=10和N=3）

我认为获得的连接会在退出时自动关闭async with。

这是重现的最小脚本：

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)

【参考方案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()之前的额外等待，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