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help / color / mirror / Atom feedFrom: Ron Johnson <[email protected]>
To: pgsql-general <[email protected]>
Subject: Re: Fillfactor effectiveness on existing table
Date: Tue, 10 Feb 2026 12:28:03 -0500
Message-ID: <CANzqJaBcssS-inkrW=cxqxd5_1-Re-0xY6totprgypSHC-mkmg@mail.gmail.com> (raw)
In-Reply-To: <CAKFQuwYppwZRZQ128T+z638iMNGYcuLGHw42DD_AKSTnZu9QVQ@mail.gmail.com>
References: <CAJCZko+BFu4c4moqA5kMoJx3776xdYfEsxJQVNu_YYgrBmsCyQ@mail.gmail.com>
<CAKFQuwYppwZRZQ128T+z638iMNGYcuLGHw42DD_AKSTnZu9QVQ@mail.gmail.com>
On Tue, Feb 10, 2026 at 11:05 AM David G. Johnston <
[email protected]> wrote:
> On Tuesday, February 10, 2026, Durgamahesh Manne <
> [email protected]> wrote:
>
>> Hi
>>
>> I added fillfactor with less than 100 to existing table then ran vacuum
>> full to take effect
>>
>> How to ensure the applied fillfactor is working successfully
>>
>> A ratio of hot updates in catalog table should higher than value of
>> n_dead_tup or n_tup_upd? Or what ?
>>
>>
> While free space on the page is necessary for HOT, it is not sufficient.
>
> If you want to prove fillfactor isn’t buggy I’d suggest contriving a test
> case instead inspecting complex real data. A table with a single bigint
> and say 50 fillfactor should be easily visible when inspecting the free
> space of a page in the heap (not sure of the exact query for this though).
> There is a page-inspect contrib extension that provides low-level details.
>
What about pgstattuple.free_space and free_percent?
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