pgAgent is a scheduling agent that runs and manages jobs; each job consists of one or more steps and schedules. If two or more jobs are scheduled to execute concurrently, pgAgent will execute the jobs in parallel (each with it’s own thread).
A step may be a series of SQL statements or an operating system batch/shell script. Each step in a given job is executed when the previous step completes, in alphanumeric order by name. Switches on the pgAgent Job dialog (accessed through the Properties context menu) allow you to modify a job, enabling or disabling individual steps as needed.
Each job is executed according to one or more schedules. Each time the job or any of its schedules are altered, the next runtime of the job is re-calculated. Each instance of pgAgent periodically polls the database for jobs with the next runtime value in the past. By polling at least once every minute, all jobs will normally start within one minute of the specified start time. If no pgAgent instance is running at the next runtime of a job, it will run as soon as pgAgent is next started, following which it will return to the normal schedule.
When you highlight the name of a defined job in the pgAdmin tree control, the Properties tab of the main pgAdmin window will display details about the job, and the Statistics tab will display details about the job’s execution.
pgAgent is a very powerful tool, but does have some security considerations that you should be aware of:
Database password - DO NOT be tempted to include a password in the pgAgent connection string - on Unix systems it may be visible to all users in ps output, and on Windows systems it will be stored in the registry in plain text. Instead, use a libpq ~/.pgpass file to store the passwords for every database that pgAgent must access. Details of this technique may be found in the PostgreSQL documentation on .pgpass file.
System/database access - all jobs run by pgAgent will run with the security privileges of the pgAgent user. SQL steps will run as the user that pgAgent connects to the database as, and batch/shell scripts will run as the operating system user that the pgAgent service or daemon is running under. Because of this, it is essential to maintain control over the users that are able to create and modify jobs. By default, only the user that created the pgAgent database objects will be able to do this - this will normally be the PostgreSQL superuser.