On 25 August 2017 at 13:21, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
>> Main is roughly what is wanted, yet it always tries to compress. If
>> you already know that won't be useful it should be possible to turn
>> compression off.
>
> If you know compression isn't useful, but you don't want to fail on
> wide values, then "external" should serve the purpose.
Well, almost. External toasts at 2048-ish bytes whereas Main toasts at
8160 bytes.
The rows are typically near 4kB long, so if marked External they would
always be toasted.
It's desirable to have the full row in the heap block, rather than
have to access heap-toastindex-toastblocks in all cases.
The data is also incompressible, so Main just wastes time on insert.
Hence, we have a missing option.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services