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From: Justin Pryzby <pryzby@telsasoft.com>
To: Mike Schanne <mschanne@kns.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: unexpected result for wastedbytes query after vacuum full
Date: Fri, 6 Dec 2019 17:28:49 -0600
Message-ID: <20191206232849.GT2082@telsasoft.com> (raw)
In-Reply-To: <db92c5c1a0904209a4ef2d857276ab4b@USEPRDEX1.corp.kns.com>
References: <db92c5c1a0904209a4ef2d857276ab4b@USEPRDEX1.corp.kns.com>

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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