Vacuum and WAL Files Creation

This document explains the impact of PostgreSQL's VACUUM command on disk space and how to prevent its usage from triggering the a9s Parachute. PostgreSQL's VACUUM command is used to reclaim storage occupied by dead tuples. To achieve this, the VACUUM command can trigger the following operations:

• Delete old row versions
• Freeze rows
• Truncate empty pages at the end of the table

These operations generate changes that are logged in Write-Ahead Logging (WAL) files. Thus, executing VACUUM on large or frequently updated tables can significantly increase the number of WAL files, consuming a lot of disk space. Since PostgreSQL retains these files for performance and recovery purposes, this can quickly reduce available disk space and potentially trigger the a9s Parachute. For more details, see a9s Parachute Concerns.

Prevention Strategies

To avoid triggering the a9s Parachute due to high disk usage:

• Increase Persistent Disk Size: Ensure sufficient disk space before executing VACUUM.
• Monitor Disk Usage: Regularly check disk space to prevent unexpected issues.

For more information on disk usage, refer to a9s PostgreSQL Resources Considerations - Disk Space.