| From: | Les <nagylzs(at)gmail(dot)com> |
|---|---|
| To: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
| Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, pgsql-performance(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Index on (fixed size) bytea value |
| Date: | 2023-06-20 07:18:31 |
| Message-ID: | CAKXe9UCKJfjtgniRmBZfz6rMvyML38xVZ6tebEui-KiHpC+ArQ@mail.gmail.com |
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| Lists: | pgsql-performance |
>
>
> Then you would ALTER the column and SET STORAGE MAIN, so that it does not
> ever use TOAST.
>
> The size limit for a row would then be 8kB minus page header minus row
> header, which
> should be somewhere in the vicinity of 8140 bytes.
>
> If you want your block size to be a power of two, the limit would be 4kB,
> which would waste
> almost half your storage space.
>
Oh I see. So if I want to save some space for future columns, then storing
about 7500 bytes in the "block bytea" column would be close to optimal,
utilizing more than 90% of the block space. I guess that the fillfactor
setting will have no effect on this table, and it does not matter if I set
it or not.
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