How to fix Concurrent index creation failed in PostgreSQL

Connect to your PostgreSQL database and query the pg_index catalog to identify invalid indexes:

SELECT
  schemaname,
  tablename,
  indexname,
  indexdef
FROM pg_indexes
WHERE indexname LIKE '%<your_index_name>%'
UNION ALL
SELECT
  ns.nspname,
  t.relname,
  i.relname,
  pg_get_indexdef(i.oid)
FROM pg_index idx
JOIN pg_class i ON i.oid = idx.indexrelid
JOIN pg_class t ON t.oid = idx.indrelid
JOIN pg_namespace ns ON ns.oid = i.relnamespace
WHERE idx.indisvalid = false
ORDER BY ns.nspname, t.relname, i.relname;

This query identifies all invalid indexes in your database. The indisvalid = false condition specifically finds indexes that failed during concurrent creation.

Remove the invalid index using DROP INDEX IF EXISTS:

DROP INDEX IF EXISTS <schema_name>.<invalid_index_name>;

Use IF EXISTS to prevent errors if the index doesn't exist. The invalid index is not used by the query planner anyway, so dropping it immediately improves INSERT/UPDATE/DELETE performance by eliminating the overhead of maintaining it.

Before retrying index creation, identify what caused the failure:

For uniqueness violations:

SELECT <column_name>, COUNT(*) FROM <table_name>
GROUP BY <column_name>
HAVING COUNT(*) > 1;

Remove or fix duplicate rows before retrying.

For active long-running transactions:

SELECT pid, usename, application_name, state, query_start
FROM pg_stat_activity
WHERE state != 'idle' AND query_start < NOW() - INTERVAL '5 minutes';

For lock conflicts:

SELECT * FROM pg_locks
WHERE NOT granted;

Check PostgreSQL logs for specific error messages that may indicate deadlocks, constraint violations, or resource exhaustion.

Evaluate whether to use CONCURRENTLY or a standard CREATE INDEX:

Use CONCURRENTLY if:
- Your table is very large (millions of rows)
- You cannot tolerate write locks on the table
- Your application can handle the longer index build time
- You have resolved the underlying cause

Use standard CREATE INDEX if:
- Your table is relatively small (< 1 GB)
- You have a maintenance window for write locks
- You need predictable, faster index creation
- The table receives minimal write traffic during creation

For most production systems, a maintenance window with standard CREATE INDEX is faster and safer than dealing with failed concurrent creations.

Create the index using your chosen method. If using CONCURRENTLY:

CREATE INDEX CONCURRENTLY <index_name> ON <table_name> (<column_name>);

For unique indexes, ensure data is clean first:

CREATE UNIQUE INDEX CONCURRENTLY <index_name> ON <table_name> (<column_name>);

If the operation fails again, check pg_stat_progress_create_index for real-time progress:

SELECT * FROM pg_stat_progress_create_index;

This shows the current phase, rows processed, and estimated time remaining. Long-running phases indicate resource or lock contention.

After successful index creation, confirm the index is valid and being used:

SELECT
  schemaname,
  tablename,
  indexname,
  indexdef,
  idx.indisvalid
FROM pg_indexes
JOIN pg_class i ON pg_indexes.indexname = i.relname
JOIN pg_index idx ON idx.indexrelid = i.oid
WHERE indexname = '<your_index_name>';

Expect indisvalid = true. Also check index size to ensure it was fully built:

SELECT
  schemaname,
  tablename,
  indexname,
  pg_size_pretty(pg_relation_size(indexrelname::regclass)) AS size
FROM pg_indexes
WHERE indexname = '<your_index_name>';

Rerun ANALYZE to update query planner statistics.