Re: Why does PostgreSQL ftruncate before unlink?

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Jon Nelson <jnelson+pgsql(at)jamponi(dot)net>
Cc: pgsql <pgsql-general(at)postgresql(dot)org>
Subject: Re: Why does PostgreSQL ftruncate before unlink?
Date: 2014-02-24 02:56:22
Message-ID: CAOR=d=16yT+mHuCaY0aBtHQURK5mAbxUYQMGJxUg+uYRdC1ktw@mail.gmail.com
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On Fri, Feb 21, 2014 at 4:14 PM, Jon Nelson <jnelson+pgsql(at)jamponi(dot)net> wrote:
> When dropping lots of tables, I noticed postgresql taking longer than
> I would have expected.
>
> strace seems to report that the largest contributor is the ftruncate
> and not the unlink. I'm curious what the logic is behind using
> ftruncate before unlink.
>
> I'm using an ext4 filesystem.

I'm guessing that this is so that it can be rolled back. Unlink is
likely issued at commit;

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