PostgreSQL Vacuum and Vacuum full are not two different processes

 PostgreSQL’s VACUUM and VACUUM FULL are not separate processes but rather different operational modes of the same maintenance command. Here’s why:

Core Implementation

Both commands share the same underlying codebase and are executed through the vacuum_rel() function in PostgreSQL’s source code (src/backend/commands/vacuum.c). The key distinction lies in the FULL option, which triggers additional steps:

• Standard VACUUM:
  • Removes dead tuples (obsolete rows) and marks space reusable within PostgreSQL
  • Updates the visibility map to optimize future queries
  • Runs concurrently with read/write operations
• VACUUM FULL:
  • Rewrites the entire table into a new disk file, compressing it and reclaiming space for the operating system
  • Rebuilds all indexes and requires an ACCESS EXCLUSIVE lock, blocking other operations

Key Differences in Behavior

Aspect	Standard VACUUM	VACUUM FULL
Space Reclamation	Internal reuse only	OS-level space release
Locking	Non-blocking	Full table lock
Performance Impact	Lightweight, incremental	Heavy, resource-intensive
Use Case	Routine maintenance	Severe table bloat remediation

 

Why They Aren’t Separate Processes

• Shared Code Path: Both use the same core logic for dead-tuple identification and cleanup. VACUUM FULL adds a table-rewrite step by calling cluster_rel()
• Configuration Integration: Parameters like autovacuum_vacuum_scale_factor apply to both, and autovacuum workers handle standard VACUUM by default
• Unified Command Structure: The FULL option is a modifier rather than a standalone tool, as seen in the SQL syntax:

PgSQL

1 2	VACUUM (FULL, ANALYZE) table_name;  -- vs. VACUUM table_name;

When to Use Each

• Standard VACUUM: Daily maintenance to prevent bloat from MVCC dead tuples
• VACUUM FULL: Rarely, for extreme cases where table size has grown uncontrollably due to long-unvacuumed updates/deletes

In summary, while their outcomes differ significantly, VACUUM and VACUUM FULL are part of a single maintenance framework, differentiated primarily by the aggressiveness of space reclamation and locking behavior.