RE: unexpected result for wastedbytes query after vacuum full

Yes, the additional bitmap could certainly explain the increase.

Thanks,
Mike

-----Original Message-----
From: Justin Pryzby [mailto:pryzby(at)telsasoft(dot)com]
Sent: Friday, December 06, 2019 6:29 PM
To: Mike Schanne
Cc: pgsql-performance(at)postgresql(dot)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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