Backing up a database can take various forms depending on the database choice. In most cases, there will be the command line option and a graphical user interface option that functions by using the command line behind the scenes. These steps are important to save the data and state of the database to be able to recover from if there are any issues. There are different types of database backup options such as full or partial data as well as being able to choose to back up data or structures.
In PostgreSQL databases, we have the pg_dump and pg_dumpall tools. These will not work within the web interface tool as the tool is logged into PostgreSQL already. However, if you have PostgreSQL installed locally, you can test the commands.
The pg_dump tool will be able to output all of the contents of all database objects into a single file. The script dumps contain SQL commands that are in plain-text files that can be used to reconstruct the database back to the state that it was in when the database was backed up.
There can be a lot of different parameters that can be used so we will explore some of the more common options.
Let us first look at a complete command that will back up the mydb database to mydb.sql file that’s in the c:\backups\ folder on a Windows system using the user adminrole:
pg_dump -U adminrole -W -F p mydb > c:\backup\mydb.sql
Breaking this down, the pg_dump is the command line tool. The -U adminrole specifics the user role that will be used to connect to the database. In this case, we are using the adminrole to login to perform the backup. The -W will prompt the pg_dump command to prompt for the password on adminrole before it can continue. The -F specifics the output file format. In this case, the p stands for plain-text SQL script file. Then we indicate the database that we want to backup which is mydb. The > c: :\backup\mydb.sql is the output backup file name and path that we are backing up to. If we don’t pass in a path, you can just include the file name which will output the backup file to the current directory that you are running the command in.
Those would be some of the common choices but let us explore some other options. The -a option will only dump out the data but not the schema with the data definitions like the table structure. This approach is only useful if we back up the data in plain text as it will allow us to export just the data.
The -s will dump out just the object definitions like the tables rather than including the data.
The -c with the lowercase c will clean the database objects by drop statements first before creating them.
The -t will only dump out specific tables that match the table name that is passed like -t employee would only dump out the employee table. The -T with a capital T will dump out all tables other than the ones that are listed.
The -C with a capital letter will start the output with a command to create the database and reconnect to the created database. This option allow you to avoid having to create the database first
With the -F option to indicate the format, we looked at p as plain to output the plain-text SQL script. There are other options as well like “d” as directory where it will create a directory with one file for each table. There is also “t” for a tar which will create an archive file similar to a .zip file.
There is also the pg_dumpall command if you wanted to dump out all of the databases within a server. This is not a commonly used option as you typically will only want to back up specific databases at a time. The process will export all of the databases one after another in a single file so restoring from this can be unreliable. All of the options with the commands will be the same as the pg_dump command. The only difference is that the -W option is not used as you wouldn’t want to have to type the password for each individual database.
Source: Authored by Vincent Tran