System catalog reindexing is restricted in PostgreSQL. This error occurs when attempting concurrent reindexing of system catalogs or when system indexes become corrupted. Recovery requires specific techniques depending on the severity of corruption.
PostgreSQL system catalogs are critical internal tables that store metadata about the database structure. These catalogs maintain their own indexes which are essential for database operations. When these indexes become corrupted (due to bugs, hardware failures, or power loss), PostgreSQL restricts how they can be rebuilt to prevent further damage. The "Cannot reindex system catalog" error indicates you've tried to reindex system catalogs concurrently, which PostgreSQL does not allow, or that the system catalogs themselves have become corrupted and need recovery.
If you're using reindexdb --concurrently or REINDEX ... CONCURRENTLY, this is expected behavior. PostgreSQL intentionally skips system catalogs during concurrent reindexing operations.
To reindex only user tables concurrently:
REINDEX DATABASE CONCURRENTLY;Or reindex system catalogs separately (non-concurrently):
REINDEX SYSTEM;If system indexes appear corrupted, reindex them without the CONCURRENTLY option. Connect to your database and run:
REINDEX SYSTEM;For a specific corrupted index:
REINDEX INDEX pg_class_oid_index;If you know which table's indexes are corrupted:
REINDEX TABLE pg_class;If system catalog corruption is so severe that you cannot connect to PostgreSQL:
1. Stop the PostgreSQL server:
sudo systemctl stop postgresql2. Edit postgresql.auto.conf (or postgresql.conf):
sudo nano /var/lib/postgresql/data/postgresql.auto.conf3. Add the line:
ignore_system_indexes = true4. Start PostgreSQL:
sudo systemctl start postgresql5. Connect and reindex:
REINDEX SYSTEM;
REINDEX DATABASE;6. Remove the ignore_system_indexes parameter and restart PostgreSQL.
If the above methods fail, start PostgreSQL in single-user mode with the -P flag to bypass system indexes:
pg_ctl stop -D /var/lib/postgresql/data
postgres -D /var/lib/postgresql/data -PThen run from a separate terminal:
psql -h localhost -U postgresInside psql:
REINDEX SYSTEM;
REINDEX DATABASE;
\qExit single-user mode by typing q at the postgres prompt.
After reindexing completes successfully:
1. Exit single-user mode or the ignore_system_indexes parameter mode
2. Stop PostgreSQL gracefully:
sudo systemctl stop postgresql3. Remove ignore_system_indexes from config if you added it
4. Restart PostgreSQL normally:
sudo systemctl start postgresql5. Verify database is functioning:
psql -U postgres -c "SELECT 1;"System catalog corruption is rare in modern PostgreSQL versions but can occur due to hardware failures or bugs. The key principle is that concurrent reindexing is a non-blocking operation designed for user indexes only; system catalogs are too critical for concurrent rebuilding. If you encounter this error during normal REINDEX CONCURRENTLY operations, it's not an error condition—PostgreSQL is correctly skipping system catalogs. However, if you're experiencing actual system catalog corruption, the recovery process depends on how severe it is. The ignore_system_indexes parameter is a powerful recovery tool that tells PostgreSQL to skip validation of system indexes, allowing connections even when system indexes are corrupt. After recovery, always remove this parameter as it disables important safety checks. On some systems, using reindex_concurrently with REINDEX SYSTEM may have been attempted in older PostgreSQL versions; ensure you're using PostgreSQL 12 or later where this is properly restricted.
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