DDL change in multiple postgresql instances at the same time? - postgresql

Question

There are 4 postgresql instances running on 1 server. I want to make ddl change in all of them at same time.
How can I do this?

Answer 1

Write a shell script (if you're on *nix) or .cmd batch file / .vbs (if you're on Windows) to do it. Have the script invoke psql -f /path/to/ddl.sql and the IP/port, database name, etc.
Alternately, write a script in a language like Python that has proper PostgreSQL bindings. Have the script loop through the databases and run the DDL for each. In Python, for example, the following (untested) script should do the trick:
import psycopg2
conn_definitions = [
"dbname=db1 port=5432 host=127.0.0.1",
"dbname=db2 port=5432 host=127.0.0.1",
"dbname=db3 port=5432 host=127.0.0.1",
"dbname=db4 port=5432 host=127.0.0.1",
]
ddl = """
CREATE TABLE blah (
blah integer
);
CREATE INDEX blah_blah_idx ON blah(blah);
"""
connections = []
cursors = []
for conn_info in conn_definitions:
conn = psycopg2.connect(conn_info)
curs = conn.cursor()
cursors.append(curs)
connections.append(conn)
for curs in cursors:
curs.execute("BEGIN;")
for curs in cursors:
curs.execute(ddl)
for curs in cursors:
curs.execute("COMMIT;")
for conn in connections:
conn.close()
Enhance if desired by doing things like splitting the DDL into an array of statements you loop over so you can do per-statement error handling.
You could also generate the connections dynamically by connecting to one DB for each host and running select datname from pg_database to get a listing of other DBs.