I'm using psycopg2 library to connection to my postgresql database. Every time I want to execute any query, I make a make a new connection like this:
import psycopg2
def run_query(query):
with psycopg2.connect("dbname=test user=postgres") as connection:
cursor = connection.cursor()
cursor.execute(query)
cursor.close()
But I think it's faster to make one connection for whole app execution like this:
import psycopg2
connection = psycopg2.connect("dbname=test user=postgres")
def run_query(query):
cursor = connection.cursor()
cursor.execute(query)
cursor.close()
So which is better way to connect my database during all execution time on my app?
I've tried both ways and both worked, but I want to know which is better and why.
CodePudding user response:
Both ways are bad. The fist one is particularly bad, because opening a database connection is quite expensive. The second is bad, because you will end up with a single connection (which is too few) one connection per process or thread (which is usually too many).
Use a connection pool.
CodePudding user response:
You should strongly consider using a connection pool, as other answers have suggested, this will be less costly than creating a connection every time you query, as well as deal with workloads that one connection alone couldn't deal with.
Create a file called something like mydb.py, and include the following:
import psycopg2
import psycopg2.pool
from contextlib import contextmanager
dbpool = psycopg2.pool.ThreadedConnectionPool(host=<<YourHost>>,
port=<<YourPort>>,
dbname=<<YourDB>>,
user=<<YourUser>>,
password=<<YourPassword>>,
)
@contextmanager
def db_cursor():
conn = dbpool.getconn()
try:
with conn.cursor() as cur:
yield cur
conn.commit()
"""
You can have multiple exception types here.
For example, if you wanted to specifically check for the
23503 "FOREIGN KEY VIOLATION" error type, you could do:
except psycopg2.Error as e:
conn.rollback()
if e.pgcode = '23503':
raise KeyError(e.diag.message_primary)
else
raise Exception(e.pgcode)
"""
except:
conn.rollback()
raise
finally:
dbpool.putconn(conn)
This will allow you run queries as so:
import mydb
def myfunction():
with mydb.db_cursor() as cur:
cur.execute("""Select * from blahblahblah...""")