Slow initial query on postgres backend when using enum columns #281
Description
Python version: 3.8
Databases version: 0.4.1
I haven't quite figured out why this is happening, but I have made a minimal test case where you can see the problem in action. I am hoping someone here may be able to help me debug further what is going on.
The problem appears to be to do with the Postgres Enum column type, and only occurs on the initial call of fetch_all after calling connect. After the initial call to fetch_all all subsequent queries run at the expected speed, but the initial query has a ~2 second delay. Calling disconnect then connect again appears to reset this.
In our actual use case we only have one Enum column, but for the minimal test case it seems I need two Enum columns to trigger the delay.
Minimal test case:
import asyncio
import time
from enum import Enum as PEnum
from databases import Database
from sqlalchemy import Column, Enum, create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.sql.sqltypes import BigInteger
DB_URL = "postgresql://user:password@localhost:5432/testdb"
Base = declarative_base()
db = Database(DB_URL)
class MyEnum1(PEnum):
ONE = 'One'
TWO = 'Two'
class MyEnum2(PEnum):
THREE = 'Three'
FOUR = 'Four'
class MyTable(Base):
__tablename__ = "mytable"
id = Column(BigInteger, primary_key=True)
my_column_1 = Column(Enum(MyEnum1))
my_column_2 = Column(Enum(MyEnum2))
my_table = MyTable.__table__
async def read_rows(calltime: str):
query = my_table.select()
print()
print("Using query: ")
print(query)
print()
start = time.time()
rows = await db.fetch_all(query=query)
print(f"{calltime} fetch_all took: {time.time() - start} seconds")
return rows
async def async_main():
await db.connect()
await read_rows("first")
await read_rows("second")
await db.disconnect()
def main():
engine = create_engine(DB_URL)
session = scoped_session(sessionmaker(bind=engine))
Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)
loop = asyncio.get_event_loop()
loop.run_until_complete(async_main())
if __name__ == "__main__":
main()When I run this I see:
scite-api-fastapi-BjBDzBrP-py3.8 > python -m testdb
Using query:
SELECT mytable.id, mytable.my_column_1, mytable.my_column_2
FROM mytable
first fetch_all took: 2.0069031715393066 seconds
Using query:
SELECT mytable.id, mytable.my_column_1, mytable.my_column_2
FROM mytable
second fetch_all took: 0.0011420249938964844 secondsWhen I remove one of the Enum columns (delete the line my_column_2 = Column(Enum(MyEnum2))) I see:
Using query:
SELECT mytable.id, mytable.my_column_1
FROM mytable
first fetch_all took: 0.17796087265014648 seconds
Using query:
SELECT mytable.id, mytable.my_column_1
FROM mytable
second fetch_all took: 0.0005922317504882812 secondsIt runs much quicker!
Does anyone have an idea of what might be causing this?