Database Efficiency 101: Understanding Bloat, Vacuum, and the Power of pg_repack

In a high-performance database environment, how we manage storage is just as important as how we write our queries. To keep our systems…

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Database Efficiency 101: Understanding Bloat, Vacuum, and the Power of pg_repack

In a high-performance database environment, how we manage storage is just as important as how we write our queries. To keep our systems fast and cost-effective, we need to address a natural phenomenon in PostgreSQL known as Bloat.

1. What is Database Bloat?

PostgreSQL uses a system called MVCC (Multi-Version Concurrency Control). When a row is updated, Postgres doesn’t overwrite the old data; it creates a new version of the row and marks the old one as “dead.” Similarly, deleted rows are merely marked as dead tuples.

These dead tuples are “ghosts” — they occupy physical space on the disk but are invisible to your application. Bloat is the accumulation of these dead tuples within your tables and indexes.

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2. The Maintenance Arsenal

The Autovacuum (Your Internal Autopilot)

The Autovacuum daemon is a background process that automatically cleans up dead tuples so the space can be reused. To keep it efficient, we focus on three main settings:

• Scale Factor (**autovacuum_vacuum_scale_factor**): This determines the threshold for when a vacuum starts. For example, a 20% scale factor means 20% of a table must be "dead" before a cleanup triggers.
• Cost Delay (**autovacuum_vacuum_cost_delay**): This tells the worker to "pause" occasionally to ensure it doesn't consume all your Disk I/O, protecting application performance.
• Workers: This is the number of parallel processes allowed to clean the database at once.

VACUUM FULL (The Heavy Reset)

VACUUM FULL physically rewrites a table to a new file, reclaiming 100% of the bloat and returning that space to the Operating System.

• The Problem: It requires an Access Exclusive Lock, meaning no one can read or write to the table while it’s running. In a 24/7 environment, this is rarely an option.

pg_repack (The Professional Solution)

pg_repack offers the best of both worlds. It reclaims 100% of the bloat and returns space to the OS, but it does so online.

• How it works: It creates a new “clean” version of the table in the background, logs new changes, and then swaps them in a fraction of a second at the very end.

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3. Why is Bloat Removal Necessary?

• Faster Querying: Bloat forces the database to read through “empty” space during scans. Removing bloat reduces Disk I/O and speeds up response times.
• Cost Optimization: We pay for the storage we provision. Our audit identified over 620 GB of recoverable “ghost” space. Reclaiming this reduces our infrastructure spend.
• System Stability: Excessive bloat makes indexes larger and slower to update, eventually leading to performance “jitter” during peak traffic.

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4. Our Execution Strategy

To minimize risk, we process the database using a Sequential Repack Strategy. Instead of a massive operation, we process one table at a time. This ensures that the maximum additional storage required is only the size of the largest single table being processed, rather than a doubling of our entire database footprint.

By clearing out the 90%+ bloat found in our smaller tables first, we create a “buffer” of free space to safely handle our largest multi-terabyte partitions.

By Jatin Jain Saraf on March 13, 2026.