Use DELETE FROM instead of TRUNCATE for pgx

[HeroSizy]

Problem

In PostgreSQL, TRUNCATE statements cannot run during a db backup.

Deployment would be blocked by db_dump if there would be migration to run.

db_dump requires ACCESS SHARE LOCK

Reference:
https://www.postgresql.org/docs/current/app-pgdump.html

And will conflict with TRUNCATE which requires ACCESS EXCLUSIVE LOCK

Solution

Use DELETE FROM instead of TRUNCATE for clearing the table since there is only one row of record

Reference

Postgres

https://www.postgresql.org/docs/current/sql-truncate.html

Article about this scenario

https://www.dbi-services.com/blog/when-we-do-a-pg_dump-and-right-afterwards-truncate-a-table-which-is-in-the-dump-what-happens/

Edits

---

Edit 28-Feb-2024

• Added support for pgx/v5 driver as well

[shawnzxx]

I was facing the same issue too.
Yes, the pg_dump operation is blocking the truncate, can refer to this article

Can we change from TRUNCATE to DELETE like @HeroSizy proposed in his PR?

[coveralls]

coverage: 56.314%. remained the same
when pulling 2168b7a on HeroSizy:pg-db-dump-truncate-fix
into 2788339 on golang-migrate:master.

[HeroSizy]

@dhui Any updates on getting this merged? Appreciate for your time.

[dhui]

@HeroSizy @shawnzxx Sorry for the extremely slow response. I'm onboard with the change. A similar change was already made to MySQL but for different reasons. Could you also make the change to the postgres driver?

Also, based on the article you linked, be aware that if there any migrations (e.g. DDL statements) that need to be applied, they'd still be blocked by the pg_dump run. SetVersion() should only be called if there are migrations that need to be applied.

[HeroSizy]

Hi @dhui , apologise for the slow response, I have just updated the isolation level. And also included pgx/v5