How to Fix PostgreSQL Error: Cache Lookup Failed

The "Cache lookup failed" error occurs when PostgreSQL cannot find expected metadata in its system catalogs, often due to concurrent DDL operations or catalog inconsistencies.

Impact

Causes query failures and can indicate system catalog corruption or concurrency issues with schema changes.

Common Causes

1. Concurrent DDL operations
2. Dropping objects while in use
3. System catalog corruption
4. Transaction isolation issues
5. Prepared statements on altered objects

Troubleshooting and Resolution Steps

1. Retry the operation:

   -- Often transient, retry query
   -- Close and reopen connection if persistent
   

2. Avoid concurrent DDL:

   -- Don't drop/alter tables during active queries
   -- Use proper locking for schema changes
   BEGIN;
   LOCK TABLE mytable IN ACCESS EXCLUSIVE MODE;
   ALTER TABLE mytable ADD COLUMN new_col INTEGER;
   COMMIT;
   

3. Invalidate prepared statements:

   # Close and reopen connection
   conn.close()
   conn = psycopg2.connect(...)
   

Additional Information

• Usually caused by concurrent schema changes
• Close connections after DDL operations
• Coordinate schema changes carefully
• Rarely indicates actual corruption

Frequently Asked Questions

Q: Is this a serious error?
A: Usually not. Often caused by timing of concurrent operations. Retry typically works.

Q: How do I prevent it?
A: Coordinate DDL changes, use connection pooling with statement invalidation, avoid DDL during peak usage.