What is bloat (swelling) of tables and indexes? How to fight it?

Bloat (table and index swelling) is a situation where the database physically occupies more space than needed for storing current data. This occurs due to the accumulation of "dead" or outdated records that have not been deleted or compressed after update or delete operations.

Causes of bloat:

• MVCC (multi-version concurrency control) in DBMS, for example in PostgreSQL, where updating creates new versions of rows, and old ones remain until cleaned.
• Frequent updates and deletions without subsequent cleanup.

Problems from bloat:

• Increased database size, which slows down queries and backups.
• Increased load on disk and memory.

How to combat bloat:

1. Automatic or manual cleanup:

   • In PostgreSQL — the VACUUM command (usually VACUUM FULL for thorough cleaning).
   • ANALYZE to update statistics.

2. Reorganizing tables and indexes:

   • REINDEX for indexes.
   • CLUSTER for physically reorganizing the table.

3. Configuring DBMS parameters:

   • Automatic autovacuum.
   • Proper thresholds for cleanup.

4. Query optimization:

   • Minimize frequent updates and deletions.
   • Use partitioning for large tables.

Example in PostgreSQL:

-- Check for bloat using extensions (pgstattuple)
SELECT * FROM pgstattuple('your_table');

-- Clean up the table
VACUUM FULL your_table;

-- Rebuild indexes
REINDEX TABLE your_table;

Thus, regular database maintenance helps control bloat and maintain performance.