Re: tuple data size and compression

>
> https://www.postgresql.org/docs/9.5/static/storage-toast.html
>>
>
> "The TOAST management code is triggered only when a row value to be stored
> in a table is wider than TOAST_TUPLE_THRESHOLD bytes (normally 2 kB). The
> TOAST code will compress and/or move field values out-of-line until the row
> value is shorter than TOAST_TUPLE_TARGET bytes (also normally 2 kB) or no
> more gains can be had. During an UPDATE operation, values of unchanged
> fields are normally preserved as-is; so an UPDATE of a row with out-of-line
> values incurs no TOAST costs if none of the out-of-line values change."
>
> Pupillo
>>
> --
>>
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com

I see. But in my case rows don't reach that thresold (I didn't check if 2K
but I didn't change anything). So I'm wondering if there is any other
chance except the TOAST to get the rows compressed or not.
I noticed that, when I use constant data, the total IO writes (by iostat)
are more or less 1/2 of the the total IO writes when using random or other
data hard to compress.