How to fix Concurrent index creation failed in PostgreSQL

PostgreSQLINTERMEDIATEMEDIUMUpdated Dec 28, 2025· 221 views

When CREATE INDEX CONCURRENTLY fails, PostgreSQL leaves behind an invalid index that consumes resources without providing query benefits. You must identify and remove the invalid index, then resolve the underlying cause before retrying index creation.

Quick fix

Fixes Concurrent index creation failed

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;
  1. Check for invalid indexes using pg_index
  2. Drop the invalid index
  3. Investigate the root cause
  4. Decide between CONCURRENTLY vs non-concurrent creation
postgresql — error
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;
Concurrent index creation failed

What this error means

This error occurs when PostgreSQL's concurrent index creation process fails during one of its three phases: catalog entry creation, first table scan, or second table scan. Unlike regular CREATE INDEX which acquires a full SHARE lock, CONCURRENTLY uses a SHARE UPDATE EXCLUSIVE lock that allows concurrent writes. However, if a deadlock, uniqueness violation, lock timeout, or other constraint violation occurs during the two table scans, the index is marked INVALID and left behind in the system catalogs. This orphaned invalid index still gets updated on every INSERT, UPDATE, and DELETE operation, consuming memory and I/O resources while being ignored during query planning.

Typical symptoms

  • Index creation commands complete without error but indexes appear non-functional
  • Query performance remains poor despite index creation attempt
  • Database size increases without apparent reason
  • Slow DML operations (INSERT, UPDATE, DELETE) due to maintaining invalid indexes
  • Error logs show "Concurrent index creation failed" or related lock timeouts

Common causes

  1. Deadlock between concurrent transactions during the index building phase
  2. Duplicate values inserted into a unique index between the two table scans
  3. Lock timeout or long-running transaction blocking the index creation
  4. Data corruption or constraint violations detected during index scan
  5. Insufficient resources (memory, disk) during index construction
  6. Transaction isolation conflicts during the multi-phase indexing process

How to fix "Concurrent index creation failed"

1Check for invalid indexes using pg_index

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

sql
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.

2Drop the invalid index

Remove the invalid index using DROP INDEX IF EXISTS:

sql
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.

3Investigate the root cause

Before retrying index creation, identify what caused the failure:

For uniqueness violations:

sql
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:

sql
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:

sql
SELECT * FROM pg_locks
WHERE NOT granted;

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

4Decide between CONCURRENTLY vs non-concurrent creation

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.

5Retry index creation with error handling

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

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

For unique indexes, ensure data is clean first:

sql
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:

sql
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.

6Verify index validity after creation

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

sql
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:

sql
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.

Advanced notes

PostgreSQL 12+ introduced REINDEX CONCURRENTLY with the same limitations as CREATE INDEX CONCURRENTLY. However, standard REINDEX does not support CONCURRENTLY in earlier versions. If you must rebuild an index during active traffic on PostgreSQL < 12, consider using pg_dump with pg_restore or creating a new index with a different name, then swapping via ALTER INDEX RENAME. For multi-schema setups (e.g., SaaS tenants), invalid indexes can proliferate—implement automated monitoring using pg_index queries in your schema discovery scripts. Additionally, CREATE INDEX IF NOT EXISTS does not prevent invalid index creation; always verify with indisvalid = true rather than relying on the IF NOT EXISTS clause.

Frequently asked questions

What does "Concurrent index creation failed" mean?
This error occurs when PostgreSQL's concurrent index creation process fails during one of its three phases: catalog entry creation, first table scan, or second table scan. Unlike regular CREATE INDEX which acquires a full SHARE lock, CONCURRENTLY uses a SHARE UPDATE EXCLUSIVE lock that allows concurrent writes. However, if a deadlock, uniqueness violation, lock timeout, or other constraint violation occurs during the two table scans, the index is marked INVALID and left behind in the system catalogs.
How do I fix "Concurrent index creation failed"?
When CREATE INDEX CONCURRENTLY fails, PostgreSQL leaves behind an invalid index that consumes resources without providing query benefits. You must identify and remove the invalid index, then resolve the underlying cause before retrying index creation.
What causes "Concurrent index creation failed"?
Deadlock between concurrent transactions during the index building phase Duplicate values inserted into a unique index between the two table scans Lock timeout or long-running transaction blocking the index creation
Is the "Concurrent index creation failed" error serious?
It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

Official resources & further reading