active_sql_transaction CREATE INDEX CONCURRENTLY cannot run inside a transaction block — 25001

Symptoms

CREATE INDEX CONCURRENTLY was issued inside a transaction block. Because it commits in multiple phases to avoid locking writes, it cannot run inside an outer transaction. PostgreSQL raises SQLSTATE 25001 (active_sql_transaction).

• Common in migration tools that wrap each step in a transaction.
• Applies to REINDEX CONCURRENTLY and DROP INDEX CONCURRENTLY too.
• Must be executed standalone with autocommit.

What the server log shows

ERROR:  CREATE INDEX CONCURRENTLY cannot run inside a transaction block

Why PostgreSQL raises this — what the manual says

the CREATE INDEX reference (Building Indexes Concurrently):

“Another difference is that a regular CREATE INDEX command can be performed within a transaction block, but CREATE INDEX CONCURRENTLY cannot.”

The concurrent build commits between internal phases so it never holds a long write lock. Running inside an outer transaction would prevent those intermediate commits, so PostgreSQL rejects it with 25001.

Common causes

• A migration framework wrapping statements in a transaction by default.
• Issuing the command after BEGIN.
• Autocommit disabled on the connection.

How to fix it

1. Run it outside a transaction (autocommit on).
2. In migration tools, mark the step as non-transactional (e.g. disable the wrapping transaction for that migration).
3. If a concurrent build fails midway, drop the leftover INVALID index and retry.

Diagnostic query

-- Find invalid indexes left by a failed concurrent build
SELECT c.relname FROM pg_index i
JOIN pg_class c ON c.oid = i.indexrelid
WHERE NOT i.indisvalid;

Related & next steps

• SQLSTATE 25001 — Active SQL Transaction (full reference)
• Message: VACUUM cannot run inside a transaction block
• Glossary: Concurrent index build

Reference: PostgreSQL 18 — CREATE INDEX.