PostgreSQL Vacuum and Vacuum full are not two different processes

PostgreSQL Vacuum and Vacuum full are not two different processes

PostgreSQL Vacuum: 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
  • Additionally, it updates the visibility map to optimize future queries
  • Moreover, it 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

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:

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.

Comprehensive Guide to Aggregate Functions in PostgreSQL

PostgreSQL Vacuum Internals – What happens during PostgreSQL Vacuum Processing?