require-concurrent-index-drop

Reports DROP INDEX without CONCURRENTLY, which blocks reads and writes on the table while it waits and runs.

Category	Default severity	Databases
locking	warn	PostgreSQL

What happens

A plain DROP INDEX takes an ACCESS EXCLUSIVE lock on the index's table. The drop itself is quick, but the lock must first wait for every query already running on the table. While it waits, every new query on the table, including plain reads, waits behind it. One slow query can stop all traffic to the table.

DROP INDEX CONCURRENTLY waits for running queries without taking that lock, so reads and writes continue. Like other concurrent index operations, it cannot run inside a transaction (see concurrent-index-transaction).

An index created earlier in the same migration is not reported, since nothing uses it yet.

Bad

What migration:generate writes when an @Index() is removed:

import { MigrationInterface, QueryRunner } from 'typeorm'

export class DropUserEmailIndex1727200000000 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`DROP INDEX "public"."IDX_users_email"`)
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    // ...
  }
}

Safe

import { MigrationInterface, QueryRunner } from 'typeorm'

export class DropUserEmailIndex1727200000000 implements MigrationInterface {
  transaction = false

  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.query(`DROP INDEX CONCURRENTLY "public"."IDX_users_email"`)
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    // ...
  }
}

With migrationsTransactionMode: "each" in the DataSource, and in orm-preflight.config.json:

{ "typeorm": { "transactionMode": "each" } }

When to suppress

When the table is small and quiet, or the migration runs in a maintenance window.

// preflight safety-assured require-concurrent-index-drop -- internal table, no traffic during deploys

References

• PostgreSQL: DROP INDEX ("A normal DROP INDEX acquires an ACCESS EXCLUSIVE lock on the table, blocking other accesses until the index drop can be completed. With this option, the command instead waits until conflicting transactions have completed.")
• orm-preflight lock verification results (a SELECT waits behind a waiting ALTER)