How to fix Index is corrupted in PostgreSQL

PostgreSQLADVANCEDCRITICALUpdated Dec 28, 2025· 198 views

PostgreSQL indexes can become corrupted due to hardware failures, software bugs, or unexpected data issues. Use REINDEX or CREATE INDEX CONCURRENTLY to rebuild the corrupted index and restore database integrity.

Quick fix

Fixes Index is corrupted

CREATE EXTENSION IF NOT EXISTS amcheck;
  1. Verify the corruption with amcheck extension
  2. Create a backup before proceeding
  3. Rebuild the corrupted index using REINDEX
  4. Use REINDEX CONCURRENTLY for minimal downtime (PostgreSQL 12+)
postgresql — error
CREATE EXTENSION IF NOT EXISTS amcheck;
Index is corrupted

What this error means

An index corruption occurs when the internal structure of a PostgreSQL index becomes invalid or inconsistent with the actual table data. This happens rarely but can be caused by hardware failures (RAID controller issues, power loss), software bugs, or filesystem errors. When an index is corrupted, database queries may return incorrect results, missing rows, or fail entirely. The optimizer may stop using the corrupted index, falling back to slow sequential scans. In critical cases, corrupted system indexes can prevent the entire database from starting.

Typical symptoms

  • Queries return fewer or more rows than expected
  • Queries that should use indexes are performing sequential scans instead
  • Database connections fail at startup with "index contains unexpected zero page"
  • Query performance degrades significantly for specific tables
  • Applications report missing or duplicate data

Common causes

  1. Hardware failure: RAID controller with faulty battery backup, worn-out storage media
  2. Power loss during index write operation before data was synced to disk
  3. PostgreSQL software bug affecting index page management
  4. Filesystem corruption or OS-level storage issues
  5. Duplicate rows appearing in a table with a UNIQUE index constraint
  6. Issues with CREATE INDEX CONCURRENTLY operation interruption

How to fix "Index is corrupted"

1Verify the corruption with amcheck extension

First, enable the amcheck extension and test your indexes:

sql
CREATE EXTENSION IF NOT EXISTS amcheck;

Then check specific indexes:

sql
SELECT * FROM bt_index_check('index_name'::regclass);

For a comprehensive check including heap verification:

sql
SELECT * FROM bt_index_parent_check('index_name'::regclass);

If amcheck returns errors, the index is corrupted and needs rebuilding.

2Create a backup before proceeding

Always back up your database before attempting index repairs:

bash
pg_dump dbname > dbname_backup.sql

If you have pg_basebackup available:

bash
pg_basebackup -D /backup/path -Ft -z

This ensures you can recover if the repair process encounters unexpected issues.

3Rebuild the corrupted index using REINDEX

For a single index (simplest approach, but locks the table):

sql
REINDEX INDEX index_name;

To reindex all indexes on a table:

sql
REINDEX TABLE table_name;

Note: REINDEX blocks writes and indexes-based reads during execution. For large indexes, this can cause significant downtime.

4Use REINDEX CONCURRENTLY for minimal downtime (PostgreSQL 12+)

PostgreSQL 12 and later support non-blocking index rebuilds:

sql
REINDEX INDEX CONCURRENTLY index_name;

This creates a new index in the background, then swaps it with the corrupted one. The table remains fully accessible during this operation, though it uses more disk space temporarily.

5Manual rebuild for older PostgreSQL versions

If running PostgreSQL 11 or earlier, use this non-blocking approach:

sql
CREATE INDEX CONCURRENTLY index_name_new ON table_name (...) WHERE ...;
DROP INDEX CONCURRENTLY index_name;
ALTER INDEX index_name_new RENAME TO index_name;

Replace the index definition with your original index definition. This allows concurrent access throughout the operation.

6Handle UNIQUE index corruption with duplicate rows

If the corrupted index is UNIQUE, you may have duplicate rows. REINDEX will fail in this case. First, identify and remove duplicates:

sql
WITH duplicates AS (
  SELECT id, ROW_NUMBER() OVER (PARTITION BY column1, column2 ORDER BY id) as rn
  FROM table_name
)
DELETE FROM table_name WHERE id IN (
  SELECT id FROM duplicates WHERE rn > 1
);

After removing duplicates, proceed with REINDEX.

7Handle system index corruption (critical)

If a system catalog index is corrupted and preventing PostgreSQL from starting:

1. Stop the PostgreSQL server
2. Start with recovery mode:

bash
postgres --single -D /var/lib/postgresql/data -c ignore_system_indexes=on

Or edit postgresql.conf:

bash
ignore_system_indexes = on

3. Connect and rebuild the corrupted system index:

sql
REINDEX INDEX system_index_name;

4. Disable the recovery setting and restart normally.

Advanced notes

Index corruption is extremely rare in modern PostgreSQL. Most cases are caused by hardware failures—investigate your storage subsystem if indexes keep becoming corrupted. Some hardware vendors (RAID controllers) are notorious for data corruption issues. Consider using pg_repack utility for automated concurrent reindexing in production environments. Monitor index bloat with pg_stat_user_indexes and maintain healthy vacuum settings to prevent unrelated performance issues. CREATE INDEX CONCURRENTLY can itself create corrupted indexes if interrupted—always monitor the operation. For hosted PostgreSQL services (AWS RDS, Google Cloud SQL, Heroku), check their specific procedures as some automatically detect and repair index corruption.

Frequently asked questions

What does "Index is corrupted" mean?
An index corruption occurs when the internal structure of a PostgreSQL index becomes invalid or inconsistent with the actual table data. This happens rarely but can be caused by hardware failures (RAID controller issues, power loss), software bugs, or filesystem errors. When an index is corrupted, database queries may return incorrect results, missing rows, or fail entirely.
How do I fix "Index is corrupted"?
PostgreSQL indexes can become corrupted due to hardware failures, software bugs, or unexpected data issues. Use REINDEX or CREATE INDEX CONCURRENTLY to rebuild the corrupted index and restore database integrity.
What causes "Index is corrupted"?
Hardware failure: RAID controller with faulty battery backup, worn-out storage media Power loss during index write operation before data was synced to disk PostgreSQL software bug affecting index page management
Is the "Index is corrupted" error serious?
Yes. This is a critical-severity error that usually blocks work until it is fixed, but the steps above resolve it.

Official resources & further reading