Is it possible to issue a “VACUUM ANALYZE 2019-04-28 16:02发布 站内问答 / Python 1360 2 4

Question

Well, the question pretty much summarises it. My db activity is very update intensive, and I want to programmatically issue a Vacuum Analyze. However I get an error that says that the query cannot be executed within a transaction. Is there some other way to do it?

Answer 1

You can turn on Postgres autocommit mode using SQLAlchemy's raw_connection (which will give you a "raw" psycopg2 connection):

import sqlalchemy
from psycopg2.extensions import ISOLATION_LEVEL_AUTOCOMMIT


engine = sqlalchemy.create_engine(url)
connection = engine.raw_connection()
connection.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)
cursor = connection.cursor()
cursor.execute("VACUUM ANALYSE table_name")

Answer 2

This is a flaw in the Python DB-API: it starts a transaction for you. It shouldn't do that; whether and when to start a transaction should be up to the programmer. Low-level, core APIs like this shouldn't babysit the developer and do things like starting transactions behind our backs. We're big boys--we can start transactions ourself, thanks.

With psycopg2, you can disable this unfortunate behavior with an API extension: call connection.autocommit(). There's no standard API for this, unfortunately, so you have to depend on nonstandard extensions to issue commands that must be executed outside of a transaction.

No language is without its warts, and this is one of Python's. I've been bitten by this before too.