Re: unexpected result for wastedbytes query after vacuum full

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Guillaume Lelarge <guillaume(at)lelarge(dot)info>
Cc: Mike Schanne <mschanne(at)kns(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: unexpected result for wastedbytes query after vacuum full
Date: 2019-12-10 19:48:26
Message-ID: CAMkU=1zi58hnPahYjv=eNLuBoURA9HzKtrJ7TJZuxevc5yyycw@mail.gmail.com
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On Tue, Dec 10, 2019 at 11:43 AM Guillaume Lelarge <guillaume(at)lelarge(dot)info>
wrote:

This query uses the column statistics to estimate bloat. AFAIK, json
> columns don't have statistics, so the estimation can't be relied on (for
> this specific table at least).
>

This was true prior to 9.5 (for xml at least, I don't know about json), but
should not be true from that release onward. But still the difference
between 74440704 and 74506240, this does seem to me to be straining at a
gnat to swallow a camel.

Cheers,

Jeff

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