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From: Tom Lane <[email protected]>
To: vaibhave postgres <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: pg_restore: fails to restore post-data items due to circular FK deadlock
Date: Thu, 30 May 2024 11:29:29 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAM_eQjwLbRsdPF2=Yip05QNb-tyb2LXkAqfSkuVKpZRNhRmJmA@mail.gmail.com>
References: <CAM_eQjwLbRsdPF2=Yip05QNb-tyb2LXkAqfSkuVKpZRNhRmJmA@mail.gmail.com>

vaibhave postgres <[email protected]> writes:
> 1. Create a database which has circular foreign key dependencies. (or use
> the sql script which I have shared), restore the pre-data section first.
> 2. pg_dump -Fc *--section=post-data*
> 3. pg_restore --jobs > 1

> pg_restore fails to record the dependency between the foreign keys and
> tries to process them in parallel (see the attached log file for details)

The reason this works in other cases is that pg_restore recognizes
that two ADD CONSTRAINT steps shouldn't be run concurrently when they
have dependencies on the same table(s).  However, when you use
--section=post-data to create the dump file, there are no entries for
the tables.

So this seems like a "don't do that" case.  You could get the results
you want by using --schema-only at dump time and then using
--section=post-data as a pg_restore switch.  (That'd also avoid the
need to make two separate dump files.)

Possibly we should add something to the docs about this.

			regards, tom lane

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