Received: from malur.postgresql.org ([217.196.149.56])
	by arkaria.postgresql.org with esmtps
 (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <pgsql-admin-owner+archive@lists.postgresql.org>)
	id 1kFaFf-0003TF-WC
	for pgsql-admin@arkaria.postgresql.org; Tue, 08 Sep 2020 09:49:24 +0000
Received: from localhost ([127.0.0.1] helo=malur.postgresql.org)
	by malur.postgresql.org with esmtp (Exim 4.92)
	(envelope-from <pgsql-admin-owner+archive@lists.postgresql.org>)
	id 1kFaFe-0003JU-Kn
	for pgsql-admin@arkaria.postgresql.org; Tue, 08 Sep 2020 09:49:22 +0000
Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29])
	by malur.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <depesz@depesz.com>)
	id 1kFaFe-0003Hc-9e
	for pgsql-admin@lists.postgresql.org; Tue, 08 Sep 2020 09:49:22 +0000
Received: from lana.depesz.com ([88.198.49.178] helo=depesz.com)
	by magus.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <depesz@depesz.com>)
	id 1kFaFa-0005Pf-O9
	for pgsql-admin@postgresql.org; Tue, 08 Sep 2020 09:49:21 +0000
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=depesz.com;
	 s=20170201; h=In-Reply-To:Content-Type:MIME-Version:References:Reply-To:
	Message-ID:Subject:Cc:To:Sender:From:Date:Content-Transfer-Encoding:
	Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender:
	Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:
	List-Subscribe:List-Post:List-Owner:List-Archive;
	bh=HLWUCvrJ8DcScs2gBNjqxTvm5Loe1pOEBaGxSesJ1ew=; b=qRhgSZguX9Je/OrZd166zZJkSV
	Ra2aPkh1e/JE1UJgdkpIXS/E8bQUABq9DIaIP/4fimNKO3kCVEUCOm191r3eFIeLdrUksKzboOdsM
	Omol5xNide4VVWOEujbxDNOkvd+h3xH6oc33B5LpjeGSNK4zFGnviMl0+zDgdogQRQBg=;
Received: from lana.depesz.com ([88.198.49.178] helo=depesz.com)
	by depesz.com with esmtpa (Exim 4.92)
	(envelope-from <depesz@depesz.com>)
	id 1kFaFZ-00040t-IU; Tue, 08 Sep 2020 11:49:17 +0200
Date: Tue, 8 Sep 2020 11:49:17 +0200
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: ZongtianHou <zongtianhou@icloud.com>
Cc: pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: how to clean dropped column in pg_attribute
Message-ID: <20200908094917.GA11563@depesz.com>
Reply-To: depesz@depesz.com
References: <86FE93ED-B4E9-4907-8E5C-FB8A566115E7@icloud.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <86FE93ED-B4E9-4907-8E5C-FB8A566115E7@icloud.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
List-Id: <pgsql-admin.lists.postgresql.org>
List-Help: <https://lists.postgresql.org/manage/>
List-Subscribe: <https://lists.postgresql.org/manage/>
List-Post: <mailto:pgsql-admin@lists.postgresql.org>
List-Owner: <mailto:pgsql-admin-owner@lists.postgresql.org>
List-Archive: <https://www.postgresql.org/list/pgsql-admin>
Precedence: bulk

On Tue, Sep 08, 2020 at 05:38:24PM +0800, ZongtianHou wrote:
> I found dropped columns still exist in pg_attribute table. In the
> below example I drop c2 column and vacuum (full) this table and
> pg_attribute, it still exist (the last row). how can I clean it away? 

Unfortunately only by copying the table aside, and then renaming new
table.

But - the dropped attribute will not sure any disk space, as long as you
ran some vacuums.

Best regards,

depesz