Index creation fails due to deadlocks, constraint violations, lock timeouts, or disk space issues. Identify the root cause and drop any invalid indexes before retrying the CREATE INDEX operation.
When PostgreSQL encounters an error during index creation, it leaves behind an "invalid" index that can impact query performance and consume resources. This typically occurs when the database cannot acquire necessary locks, encounters duplicate values in a unique index, runs out of disk space, or experiences expression evaluation errors. The invalid index remains in the system until explicitly dropped or rebuilt.
Query pg_index to find all invalid indexes:
SELECT schemaname, tablename, indexname
FROM pg_indexes
WHERE indexname IN (
SELECT indexrelname FROM pg_index WHERE indisvalid = false
);This will show you which indexes failed to build and need attention.
Remove invalid indexes to clean up and free resources:
DROP INDEX CONCURRENTLY index_name;Use CONCURRENTLY to avoid blocking reads. If the index was created with _ccnew suffix (transient), drop it. If it has _ccold suffix (original), also drop it since the rebuild succeeded.
Check PostgreSQL logs for specific error details:
tail -f /var/log/postgresql/postgresql.logCommon issues:
- Duplicate key error: Run SELECT column, COUNT(*) FROM table GROUP BY column HAVING COUNT(*) > 1 to find duplicate values
- Disk full: Check available disk space with df -h
- Lock timeout: Terminate idle transactions with SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE state = 'idle in transaction'
Address the root cause before retrying:
- Duplicates: Remove duplicate rows or make the column unique: DELETE FROM table WHERE id NOT IN (SELECT MAX(id) FROM table GROUP BY column)
- Disk space: Free up space by archiving old data or adding storage
- Idle transactions: Educate developers to avoid leaving transactions open
- Locks: Ensure VACUUM isn't running during index creation
Once the issue is resolved, rebuild the index:
CREATE INDEX CONCURRENTLY index_name ON table_name (column_name);Use CONCURRENTLY (available in PostgreSQL 12+) to allow reads while building. For older versions:
REINDEX INDEX CONCURRENTLY index_name;If no concurrent option is available, schedule during low-traffic periods.
For expression indexes and partial indexes, test the expression separately to ensure it evaluates correctly on all rows. REINDEX operations require significant temporary disk space—potentially twice the size of the index. Monitor with EXPLAIN ANALYZE to verify the index is being used after successful creation. On production systems, always use CONCURRENTLY flag and monitor lock wait times. Consider setting lock_timeout to prevent long waits. For hardware-related corruption, run REINDEX TABLE to rebuild all indexes, but first verify the table data integrity with VACUUM ANALYZE.
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