Wondering how to use psql to restore a text dump?We can help you.

Using psql is one of the simplest ways to restore a text dump. Text dumping is a suitable importing method for small databases.

At Bobcares, we often get requests to restore text dumps, as a part of our Server Management Services.

Today, let’s discuss how to restore a text dump using psql (PostgreSQL) and see how our Support Engineers do this for our customers.

Steps for using psql to restore a text dump.

Before we begin, we have to create a text dump of the PostgreSQL database. This is done via the pg_dump command. It generates a SQL file with the needed commands to recreate the database.

An Overview:

• Step 1: Create a Text Dump Using pg_dump
• Step 2: Restore Using psql
• Common errors while using psql to restore a text dump
• 1. Invalid command while restoring sql
• 2. Improper Restoration of the Dump File/a>
• 3. Connection Issues Error Message

Step 1: Create a Text Dump Using pg_dump

First, open a terminal or command prompt and run this command:

pg_dump -U db_user -W -F p db_name > /path_of_the_dump/dump_file.sql


Here:

• U db_user: Specifies the database user.
• -W: Prompts for the password before connecting to the server.
• -F p: Indicates that the output format should be plain text (SQL).
• db_name: The name of the database we want to dump.
• /path_of_the_dump/dump_file.sql: The path where we want to save the dump file.

This command will create a SQL file that can later be used for restoration.

Step 2: Restore Using psql

After the text dump file is ready, we can restore it using psql as seen here:

psql -U db_user db_name < /path_of_the_dump/dump_file.sql

Here:

• -U db_user: Specifies the database user.
• db_name: The name of the database where we want to restore the dump.
• /path_of_the_dump/dump_file.sql: Redirects the SQL commands from the dump file into psql.

This command runs all SQL commands contained in dump_file.sql, effectively restoring the database to its previous state.

Common errors while using psql to restore a text dump

Sometimes the psql text dump restoring can end up in errors. Now, let’s see a few possible errors that occur during a text file restoration. We will also see how our Support Team fix these errors for our customers.

1. Invalid command while restoring sql

Sometimes, the psql dump restores ends up in the following error message.

psql:psit.sql:27485: invalid command \N

Here the \N denotes a null value. As seen above, the error message does not offer us much information about the error. In such situations, we will have to debug the error.

psql has an inbuilt mode ‘stop on the first error‘. So, we will switch psql to ‘stop on the first error mode’. This displays the initial trigger for the error. To switch the mode, we will use the following command:

psql -v ON_ERROR_STOP=1

We can enable “stop on the first error” mode by running:

psql -v ON_ERROR_STOP=1 -U db_user db_name < /path_of_the_dump/dump_file.sql

This command will stop execution at the first error, helping us identify and fix it more easily.

2. Improper Restoration of the Dump File

At times we will encounter the following error message.

pg_restore: [archiver] input file appears to be a text format dump. Please use psql.

This error message is seen when the user tries to restore a text-based dump file using the pg_restore tool.

Usually, the pg_dump tool creates a dump file in text format. A single step restoration of a text file is only possible by using psql.

In order to use pg_restore, we must convert the text file to tar format and then execute the restore command.

So, to fix the error, we will restore the dump file in the appropriate format.

3. Connection Issues Error Message

psql: could not connect to server: Connection refused

This error indicates that psql is unable to establish a connection to the PostgreSQL server. This could be due to various reasons, such as an incorrect host, port, or authentication issues.

In order to fix it, verify that we are using the correct hostname and port number in the connection string.

Additionally, make sure that the PostgreSQL service is running on the server. We also need to ensure that any firewall settings allow connections to the PostgreSQL port (default is 5432). Furthermore, confirm that the user has sufficient permissions to access the database.

[Still, having trouble in restoring a text dump using psql? – We will help you.]

Conclusion

In short, psql restores a text dump in the same file format. Other restoration methods use different file formats and hence need file conversion. Today, we saw the text dump restoration and discussed how our Support Engineers fix the related errors.