Indexes exist to speed up data access. They allow PostgreSQL to avoid full table scans, significantly reducing query execution time for read-heavy workloads.
From real production experience, we have observed that well-designed, targeted indexes can improve query performance by 5× or more, especially on large transactional tables.
However, indexes are not free.
And in this blog, we are going to discuss what issues unused indexes can cause and how to remove them from production systems with a rollback plan, safely
1. Why Unused Large Indexes Become a Long-Term Problem
Over time, unused indexes can silently degrade database performance. Below are some of the most common issues they cause in production systems.
1.1. Slower INSERT, UPDATE, And DELETE Operations
Every write operation must update all indexes on a table, including those that are never used by queries.
1.2. Increased Vacuum And Autovacuum Overhead
Indexes accumulate dead tuples just like tables. These must be vacuumed, increasing I/O usage and extending vacuum runtimes.
1.3. Longer Maintenance Windows
Operations such as VACUUM and REINDEX take longer as the number and size of indexes grow.
1.4. Disk Space Waste And Cache Pollution
Large unused indexes consume disk space and can evict useful data from shared buffers, reducing cache efficiency.
Because of these reasons, it is always recommended to periodically identify and safely remove unused indexes from production systems, but only through a controlled and well-validated process.
2. How To Safely Drop Unused Indexes In PostgreSQL
Below is a step-by-step, production-safe checklist that should be followed before dropping any index.
2.1. Check When System Statistics Were Last Reset
If statistics were reset recently, an index may appear unused even though it is actively required by workloads.
SELECT
datname,
stats_reset
FROM pg_stat_database
WHERE datname = current_database();An older stats_reset timestamp (or NULL, meaning statistics were never reset) provides more confidence in index usage data.
2.2. Check Whether The Index Backs Any Constraint
A large index can appear unused in statistics, but must not be dropped if it enforces a PRIMARY, UNIQUE, or FOREIGN KEY constraint.
PostgreSQL uses these indexes to guarantee data integrity and will not allow them to be dropped unless the constraint itself is explicitly removed.
SELECT
i.relname AS index_name,
c.conname AS constraint_name,
c.contype AS constraint_type,
c.conrelid::regclass AS table_name
FROM pg_constraint c
JOIN pg_class i ON i.oid = c.conindid
WHERE i.relname = '<IDX_NAME>';If this query returns rows, the index can not be dropped.
2.3. Check Index Usage Statistics
This confirms whether PostgreSQL’s query planner has used the index during query execution.
SELECT
s.indexrelname AS index_name,
s.relname AS table_name,
s.idx_scan,
s.idx_tup_read,
s.idx_tup_fetch
FROM pg_stat_user_indexes s
WHERE s.indexrelname = '<IDX_NAME>';All the counts must be 0
3. Rollback Preparation
Before dropping any index, always capture its definition so it can be recreated quickly if needed.
SELECT pg_get_indexdef('<IDX_NAME>'::regclass) AS create_index_sql;Store this output as part of your rollback plan.
4. Drop The Index Safely
Using DROP INDEX CONCURRENTLY avoids blocking reads and writes on the table, making it safe for production environments.
DROP INDEX CONCURRENTLY <IDX_NAME>;If performance issues are observed after dropping the index, the rollback plan can be used to recreate the index concurrently without impacting availability.
5. Final thoughts
Dropping unused indexes can deliver meaningful performance and maintenance benefits, but only when done carefully.
Never rely on statistics alone; always validate constraints, understand workload patterns, and prepare a rollback plan.
In production systems, correctness and stability must always take priority over cleanup speed.
