Re: unexpected result for wastedbytes query after vacuum full

Le mar. 10 déc. 2019 à 20:48, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> a écrit :

> 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.
>
>
I just checked, and you're right. There are less statistics with json, but
the important ones (null_frac and avg_width) are available for json and
jsonb datatypes. So the query should work even for tables using these
datatypes.

Thanks for the information, that's very interesting. And I apologize for
the noise.

--
Guillaume.