I have an error
pymysql.err.InternalError: Packet sequence number wrong - got 0 expected 1
after leaving my application idle (0 requests to DB) for few hours. I thought, databases module creates connection pool (it does) and recreates connections after some timeout automatically, but it doesn't.
Requirements - Python 3.8, FastAPI, databases[mysql].
Any ideas ?
main.py
.......
@app.on_event("startup")
async def startup():
await db.connect()
@app.on_event("shutdown")
async def shutdown():
await db.disconnect()
.......
db_config.py
import databases
import sqlalchemy
import os
import logging
from functools import wraps
HOST = 'mysql://user:user_passw@{host}:{port}/sw_database'.format(host=os.environ.get("DB_HOST", "127.0.0.1"),
port=os.environ.get("DB_PORT", "3306"))
db = databases.Database(HOST)
metadata = sqlalchemy.MetaData()
logger = logging.getLogger(__name__)
def perform_transaction(foo):
@wraps(foo)
async def decorate(*args, **kwargs):
async with db.connection() as connection:
async with connection.transaction():
try:
res = await foo(*args, **kwargs)
except Exception as e:
logger.error(e)
return []
return res
return decorate
endpoint example
from fastapi import APIRouter
from db_config import db, perform_transaction
router = APIRouter()
@router.get('/devices_list', responses=responses_for_devices_table)
@perform_transaction
async def get_devices_list():
query = devices.select()
return await db.fetch_all(query)
You can use the pool_recycle parameter to make sure the connection pool drops or reconnects any connections that have been lingering as idle for too long. A setting of 3600 usually works fine with MySQL - it'll recycle the connection after being idle for an hour.
You can either give it as a parameter to Database(.., pool_recycle=3600), or as an option in the connection string (...?pool_recycle=3600):
db = databases.Database(HOST, pool_recycle=3600)
.. or
HOST = 'mysql://user:user_passw@{host}:{port}/sw_database?pool_recycle=3600'.format(..)