From: Mike Schanne <mschanne@kns.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: 'pgsql-performance@postgresql.org' <pgsql-performance@postgresql.org>
Subject: RE: unexpected result for wastedbytes query after vacuum full
Date: Mon, 9 Dec 2019 23:06:52 +0000
Message-ID: <1dfe6231d70545a7a7136bb8dd7265b9@USEPRDEX1.corp.kns.com> (raw)
In-Reply-To: <20191206232849.GT2082@telsasoft.com>
References: <db92c5c1a0904209a4ef2d857276ab4b@USEPRDEX1.corp.kns.com>
<20191206232849.GT2082@telsasoft.com>
Yes, the additional bitmap could certainly explain the increase.
Thanks,
Mike
-----Original Message-----
From: Justin Pryzby [mailto:pryzby@telsasoft.com]
Sent: Friday, December 06, 2019 6:29 PM
To: Mike Schanne
Cc: pgsql-performance@postgresql.org
Subject: Re: unexpected result for wastedbytes query after vacuum full
On Fri, Dec 06, 2019 at 05:18:20PM +0000, Mike Schanne wrote:
> Hi all,
>
> This question is somewhat related to my previous question:
> https://www.postgresql.org/message-id/0871fcf35ceb4caa8a2204ca9c38e330%40USEPRDEX1.corp.kns.com
>
> I was attempting to measure the benefit of doing a VACUUM FULL on my database. I was using the query found here:
> https://wiki.postgresql.org/wiki/Show_database_bloat
>
> However, I got an unexpected result in that the "wastedbytes" value actually increased for some tables after doing the vacuum.
> I was wondering if the fact that we use a json column could be interfering with the wastedbytes calculation. Can anyone explain how wastedbytes could increase from a vacuum?
Is it due to dropped columns, like Tom explained here ?
https://www.postgresql.org/message-id/18375.1520723971%40sss.pgh.pa.us
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To: pgsql-performance@postgresql.org
Cc: mschanne@kns.com, pryzby@telsasoft.com
Subject: RE: unexpected result for wastedbytes query after vacuum full
In-Reply-To: <1dfe6231d70545a7a7136bb8dd7265b9@USEPRDEX1.corp.kns.com>
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