SBN MPC Wiki

Postgres database replication.

Note that the public database schema is a β release, and may be subject to change over the development period. Tables may be added, removed, or modified by the MPC.

If you decided to replicate a Postgres mpcbeta copy of database from SBN, please, consider "Master" side paragraph FOR YOUR INFORMATION only. Start from the "Replica" side (from the scratch).

“Master” side:

1. Make sure port 5432 is open.
2. As postgres user check postgresql.conf:

  listen_addresses should be listening to the replica address.
  wal_level = logical

3. In psql setup an account and give it at least read access to the database and tables to be replicated:

  CREATE ROLE <username> WITH REPLICATION LOGIN PASSWORD ‘<password>’;
  GRANT CREATE ON DATABASE <dbname> TO <username>;
  GRANT SELECT ON ALL TABLES IN SCHEMA public TO <username>;

4. As postgres user edit pg_hba.conf:

  In the hosts section add a line like:
  host <dbname> <username> <user_IP>/32 md5

5. Restart the postgres server.
6. In psql in the <dbname> create a publication:

  [sudo -u postgres] psql <dbname>
  CREATE PUBLICATION <pubname> FOR ALL TABLES;
  or
  CREATE PUBLICATION <pubname> FOR TABLES table1, table2, table3,...;

7. Dump the schema of all tables in the publication and send them to the replica machine:

  pg_dump -d <dbname> -t <table1> -s > <table1>_schema.sql
  pg_dump -d <dbname> -t <table2> -s > <table2>_schema.sql
  pg_dump -d <dbname> -t <table3> -s > <table3>_schema.sql
     
  (can be done for all tables at once by removing the -t option, but above method makes it easier to troubleshoot any issues).
  pg_dump -d <dbname> > <dbname>_schemas.sql

Items 1,2,6 need to be done 1 time.
Items 3,4,5 need to be done with every new replication
Item 7 could be done once, but with every new replication the <username> should be updated in every *_schema.sql file:

  GRANT SELECT ON TABLE public.neocp_events TO <username>;

“Replica” side (from the scratch):

1. Install PostgresSQL v14.x
2. Provide IP-address of the server to SBN (mamoutkine@astro.umd.edu)
3. Wait for table-structures*.sql files and shell script from SBN
4. Download tables_structure*.sql files into local server disk with reading permission for all.
5. Create an empty database (mpcbeta):

  sudo -u postgres psql
  CREATE DATABASE <dbname>

5. Add empty tables using schemas from the "master" (Run those commands from the same directory where *.sql files):

  [sudo -u postgres] psql -d <dbname> -a < <table1>_schema.sql
  [sudo -u postgres] psql -d <dbname> -a < <table1>_schema.sql
  [sudo -u postgres] psql -d <dbname> -a < <table1>_schema.sql
  or
  [sudo -u postgres] psql <dbname> < <dbname>_schemas.sql

6. Create a subscription to the master’s publication:

  sudo -u postgres psql <dbname>
  CREATE SUBSCRIPTION <subname> CONNECTION “host=<master_IP_address> port=5432 user=<username> password=<password> dbname=<dbname>” PUBLICATION <pubname>;

<pubname> in “replica” and “master” sides must match, but the <subname> must not already exist. Multiple subscribers can all connect to the same publication <pubname>.

https://www.digitalocean.com/community/tutorials/how-to-set-up-logical-replication-with-postgresql-10-on-ubuntu-18-04

7. How to check a replication:

  sudo -u postgres psql mpcbeta
  SELECT * FROM neocp_obs_archive;

Another check:

  sudo -u postgres psql mpcbeta
  SELECT * FROM pg_stat_replication;

Another check: View as a sudo latest log-file: [psql_path]/11/data/log/postgresql-[Wed].log

“Replica” side (with existing logical replication from SBN) - how to add new table(s):

1. Download all structure_only.sql file into local disk with reading permission to all
2. Add empty tables using schemas from “master”:

  [sudo -u postgres] psql -d <dbname> -a < <table1>_schema.sql

3. Modify a subscription to the master’s publication:

  sudo -u postgres psql <dbname>
  ALTER SUBSCRIPTION <subscription_name> REFRESH PUBLICATION;

"How to drop a database for complete re-start or version upgrade:

• If you have a publication and distribute data to somebody - drop the publication:

  [sudo -u postgres] psql <dbname>
  DROP PUBLICATION <pubname>;

• If you subscribed to another database and have an active connection - drop the subscription:

  [sudo -u postgres psql <dbname>]
  DROP SUBSCRIPTION IF EXISTS <subname>;

• If you subscribed to another database but connection is broken:

  ALTER SUBSCRIPTION <subname> DISABLE;
  ALTER SUBSCRIPTION <subname> SET (slot=NONE);
  DROP	SUBSCRIPTION <subname>;

• Delete database:

  [sudo -u postgres psql]
  DROP DATABASE <dbname>;

• If you would like to remove the old PosgreSQL version:

  sudo systemctl stop postgresql-11
  sudo systemctl disable postgresql-11
  sudo yum remove postgresql11

• To start a new version of database go to "Replica side (from the scratch)"