How to fix Internal error in PostgreSQL

Enable detailed error logging to capture the full stack trace:

ALTER SYSTEM SET log_min_error_statement = 'ERROR';
ALTER SYSTEM SET log_error_verbosity = 'VERBOSE';
SELECT pg_reload_conf();

Then check the PostgreSQL log files (usually in /var/log/postgresql/ or configured log directory) for the complete error message and stack trace. This identifies which subsystem failed (e.g., btree index, heap table, planner).

PostgreSQL cannot operate properly without sufficient disk space:

df -h /var/lib/postgresql

Ensure at least 10% free space is available on the partition containing the database. If disk is full or nearly full, free up space immediately and restart PostgreSQL.

Isolate which index or table is causing the error by selectively disabling indexes:

ALTER SYSTEM SET enable_bitmapscan = OFF;
ALTER SYSTEM SET enable_indexscan = OFF;
SELECT pg_reload_conf();

Rerun the failing query. If it succeeds with indexes disabled, you have index corruption. Re-enable these settings after testing:

ALTER SYSTEM RESET enable_bitmapscan;
ALTER SYSTEM RESET enable_indexscan;
SELECT pg_reload_conf();

If you identified index corruption, rebuild the problematic indexes:

REINDEX INDEX CONCURRENTLY index_name;

Or rebuild all indexes in a table:

REINDEX TABLE CONCURRENTLY table_name;

Use CONCURRENTLY to avoid locking the table. For multiple corrupted indexes, rebuild them one at a time.

If the stack trace mentions "heapam" (heap access method), the table data itself is corrupted. This requires exporting and reimporting the data:

pg_dump -U postgres -Fc your_database > backup.dump

Then drop and restore the corrupted table:

DROP TABLE corrupted_table;

Restore the table from the dump, then reload the entire database if multiple tables are affected.

Many internal errors are caused by bugs fixed in newer minor versions. Upgrade PostgreSQL safely:

# Backup first (critical!)
pg_basebackup -D /path/to/backup -Fp -Pv

# For Ubuntu/Debian
sudo apt update
sudo apt install postgresql-14  # Replace 14 with your target version

# For RHEL/CentOS
sudo yum update postgresql-server

Minor version upgrades (e.g., 14.1 to 14.5) are safe and backward-compatible. Always test in a staging environment first.

After applying fixes, restart the PostgreSQL service:

# On systemd systems
sudo systemctl restart postgresql

# Or on init.d systems
sudo service postgresql restart

Monitor the logs as it starts to ensure recovery completes successfully. If the service fails to start, check the logs for WAL recovery errors.