How to pg_restore one table and its schema from a Postgres dump? - postgresql

I am having some difficulties with restoring the schema of a table. I dumped my Heroku Postgres db and I used pg_restore to restore one table from it into my local db (it has more than 20 tables). It was successfully restored, but I was having issues when I tried to insert new data into the table.
When I opened up my database using psql, I found out that the restored table is available with all the data, but its schema has zero rows. Is there anyway I could import both the table and its schema from the dump? Thank you very much.
This is how I restored the table into my local db:
pg_restore -U postgres --dbname my_db --table=message latest.dump
Edit:
I tried something like this following the official docs, but it just gets blocked and nothing happened. My db is small, no more than a couple of megabytes and the table's schema I am trying to restore has no more than 100 row.
pg_restore -U postgres --dbname mydb --table=message --schema=message_id_seq latest.dump

As a more general answer (I needed to restore a single table from a huge backup), you may want to take a look at this post: https://thequantitative.medium.com/restoring-individual-tables-from-postgresql-pg-dump-using-pg-restore-options-ef3ce2b41ab6
# run the schema-only restore as root
pg_restore -U postgres --schema-only -d new_db /directory/path/db-dump-name.dump
# Restore per table data using something like
pg_restore -U postgres --data-only -d target-db-name -t table_name /directory/path/dump-name.dump

From the Heroku DevCenter here
Heroku Postgres is integrated directly into the Heroku CLI and offers
many helpful commands that simplify common database tasks
You can check here if your environment is correctly configured.
In this way, you can use the Heroku CLI pg:pull command to pull remote data from a Heroku Postgres database to a local database on your machine.
For example:
$ heroku pg:pull HEROKU_POSTGRESQL_MAGENTA mylocaldb --app sushi

Related

How to create a table from backup file in Postgres?

After making some schema change in table message in postgresql 13 database, the table is backed up in pgadmin4 in a file named message.sql. The schema change needs to be populated in another database. What I did is to drop the table message in that database. But I have hard time to re-create table message from the backup file messages.sql (not using CREATE table message ....). I use pg_restore to restore data but was not successful for re-creating table schema. Here is command I tried with no luck:
pg_restore --data-only -h localhost -U postgres -W -d dynamo -t messages /home/download/messages.sql
pg_restore --clean -h localhost -U postgres -W -d dynamo -t messages /home/download/messages.sql
I also tried to create an blank table (no column) called messages in the database and repeated above command, again without luck.
Here is how a new table is added to the current database:
backup the current db on the server with pg_dump
create the new database on dev PC with addition of new table
On dev PC, use pgadmin to restore the backup file in step 1 to new database created in step 2.
backup in pgadmin and create a .backup file for db in step 3.
on server, use pg_restore to overwrite the current db with new database backup file created in step 4:
pg_restore --clean -U postgres --dbname=mydb -W -h localhost --verbose /home/download/mydb.backup
open psql terminal to verify the new table

PSQL prevent "COMMENT ON" on the DB dump

We are migrating some products, one of the steps is to migrate the product databases.
I have steps to
export the existing DB pg_dump --no-owner --clean --blobs --no-privileges -U dbuser old_dbname -f bkpfile.sql
import the dump to a different DB psql -U dbuser2 new_dbname -f bkpfile.sql
The problem is the old database contains statement COMMENT ON DATABASE old_dbname IS 'Rxxxxx';
The new DB user must not have permissions on the old database and imho it's not good to refer the old database name anyway in the dump.
Is there a way to create a complete DB dump without the COMMENT ON DATABASE statement?
Edit:
PostgreSQL 9.6
Steps to reproduce:
CREATE DATABASE testdb;
COMMENT ON DATABASE testdb IS 'some comment';
CREATE TABLE xx (id int);
and then dump the database, the dump contains reference to the database name COMMENT ON DATABASE testdb IS 'some comment'; which prevents importing the backup to a new database
pg_dump --no-owner --clean --blobs --no-privileges testdb
We could manually remove the comment statement or filter the comment using different tools (grep), but manual intervention or text-based filtering on top of the backup could cause data corruption.
This comment is only dumped in PostgreSQL versions below v11. See this entry in the release notes:
pg_dump and pg_restore, without --create, no longer dump/restore database-level comments and security labels; those are now treated as properties of the database.
9.6 will go out of support soon anyway, so this is a good opportunity to upgrade.

How to restore postgresql db on Heroku

I'm totally new to Heroku and Postgres and I'm trying to figure out how to restore and access the Postgres db in Heroku. I do have backup that taken fro pgAdmin III .backup file.
Any help with how to restore the Postgres db in Heroku would be greatly appreciated.
Restore to local database
Load the dump into your local database using the pg_restore tool. If objects exist in a local copy of the database already, you might run into inconsistencies when doing a pg_restore. Pg_restore does not drop all of the objects in the database when loading the dump.
This will usually generate some warnings, due to differences between your Heroku database and a local database, but they are generally safe to ignore.
$ pg_restore --verbose --clean --no-acl --no-owner -h localhost -U myuser -d mydb latest.dump

Is there a way to repopulate with command-line a postgres db that I can't drop?

I'm looking to load a database from a backup.gz. The backup is raw sql generated from pg_dump -U postgres app_development -f backup.gz -Z9.
I've tried dropping the db with psql -Upostgres -c "drop database app_development" but I get:
ERROR: database "app_development" is being accessed by other users
DETAIL: There are 3 other sessions using the database.
The same thing happens when I use dropdb.
I don't want to dump to a non-ascii version so I don't think I can use pg_restore.
Also, I'm not sure if it helps, but all this is happening in docker.

PostgreSQL - checking if restored database has all the data as original

I backup my PostgreSQL database once a week. One time, during the restore, the restored database was 2.9GB in size, while original database size was 3.7GB. The reason for different sizes is well explained here and that's not a problem.
I back up database using:
pg_dump -U postgres database_name -f backup_file.sql.
To restore the database I use:
psql -U postgres -d target_database -f backup_file.sql.
My question is what is the best way to test and ensure that the restored database has all the data from original database?