VACUUM in PostgreSQL
Tags: apacheage, postgressql, postgres
Published: 2023-08-05 17:14:49

**VACUUM** is like a cleanup tool for PostgreSQL databases, ensuring they stay organized and efficient.
It finds and removes unnecessary data, known as dead tuples, freeing up space for new information.
Dead tuples are like expired coupons – they clutter up the database, and VACUUM gets rid of them to save space.
This process also helps speed up database searches and prevents potential issues.
In essence, VACUUM is the database's janitor, keeping things tidy and running smoothly.

**VACUUM is a crucial maintenance tool in PostgreSQL databases that has several important responsibilities:**

**Space Reclamation:** One of VACUUM's primary tasks is to free up storage space by removing obsolete and no-longer-needed data. This includes cleaning up dead tuples, which are rows that have been marked as deleted or are no longer visible to active transactions. By clearing out these dead tuples, VACUUM ensures that storage is used efficiently and effectively.

**Data Organization:** VACUUM helps keep data organized and compact. It rearranges the remaining live tuples to reduce fragmentation, ensuring that data is stored efficiently and can be accessed more quickly during queries.

**Transaction ID Management:** PostgreSQL uses transaction IDs to keep track of database changes. As transactions occur, these IDs can accumulate, and if left unchecked, they could lead to issues. VACUUM manages these IDs, preventing them from reaching dangerous levels and avoiding potential transaction ID wraparound, which could lead to data corruption.

**Updating Statistics:** VACUUM not only cleans up data but also updates important statistics about the database. These statistics are crucial for the query planner to make informed decisions about how to execute queries efficiently. By refreshing these statistics, VACUUM contributes to better query performance.

**Preventing Bloat:** Over time, databases can become "bloated" with unnecessary data. VACUUM plays a key role in preventing such bloat by ensuring that only relevant and active data is retained, thus maintaining the database's overall health and responsiveness.

**Maintenance of Indexes:** VACUUM also maintains the health of indexes by compacting and optimizing them. This contributes to faster index lookups and more efficient query processing.

**Resource Management:** VACUUM releases resources held by old and completed transactions, preventing memory and resource leaks. This helps maintain the stability and responsiveness of the database system.

**VACUUM FULL in PostgreSQL:**
VACUUM FULL is a database maintenance command in PostgreSQL that reclaims storage space by thoroughly reorganizing tables and indexes. It removes both dead tuples and empty space, resulting in compact data storage. However, it requires exclusive locks on the target table, which can impact database availability during the operation.

**VACUUM FULL Command:**
To use VACUUM FULL, execute the following command in PostgreSQL:

```
VACUUM FULL table_name;
```

**Auto VACUUM in PostgreSQL:**
Auto VACUUM is a built-in automated maintenance process in PostgreSQL that manages routine vacuum tasks to optimize database performance. Enabled by default, it automatically removes old data and updates statistics. Configuration options in the postgresql.conf file allow fine-tuning of Auto VACUUM behavior:

1-autovacuum: Enables or disables the background autovacuum process (enabled by default).
2-autovacuum_vacuum_threshold: Sets the minimum dead rows count for table vacuuming (default: 50).
3-autovacuum_analyze_threshold: Specifies the minimum live rows count for table analysis (default: 50).
4-autovacuum_vacuum_scale_factor: Multiplier triggering vacuum based on table size (default: 0.2).
5-autovacuum_analyze_scale_factor: Multiplier triggering analysis based on table size (default: 0.1).
6-autovacuum_vacuum_cost_delay: Determines autovacuum start delay (default: 20 milliseconds).
7-autovacuum_vacuum_cost_limit: Sets the maximum rows vacuumed per operation (default: 200).

**Parallel VACUUM in PostgreSQL:**
Parallel VACUUM is a feature in PostgreSQL that allows the VACUUM operation to be executed using multiple worker processes simultaneously, enabling faster and more efficient cleanup of dead rows and optimization of storage space. This feature takes advantage of modern multi-core processors to divide the work and complete VACUUM tasks more quickly. Parallel VACUUM can significantly speed up maintenance operations on large tables, reducing the time required for maintenance tasks and improving overall database performance.

To enable Parallel VACUUM, ensure that your PostgreSQL configuration settings support parallelism, including `max_worker_processes` and `max_parallel_workers`. Additionally, when running a VACUUM command, you can use the `PARALLEL` option to specify the number of parallel workers to use for the operation, based on the available system resources and the characteristics of the database workload.

**REF:**
[Postgresql Documentation](https://www.postgresql.org/docs/current/sql-vacuum.html)
[PostgreSQL Vacuuming Command to Optimize Database Performance](https://www.percona.com/blog/postgresql-vacuuming-to-optimize-database-performance-and-reclaim-space/)