Re: Initdb-time block size specification

Hi,

On 2023-06-30 23:42:30 +0200, Tomas Vondra wrote:
> I wonder what are the conditions/options for disabling FPI. I kinda
> assume it'd apply to new drives with 4k sectors, with properly aligned
> partitions etc. But I haven't seen any particularly clear confirmation
> that's correct.

Yea, it's not trivial. And the downsides are also substantial from a
replication / crash recovery performance POV - even with reading blocks ahead
of WAL replay, it's hard to beat just sequentially reading nearly all the data
you're going to need.

> On 6/30/23 23:11, Andres Freund wrote:
> > If we really wanted to do this - but I don't think we do - I'd argue for
> > working on the buildsystem support to build the postgres binary multiple
> > times, for 4, 8, 16 kB BLCKSZ and having a wrapper postgres binary that just
> > exec's the relevant "real" binary based on the pg_control value. I really
> > don't see us ever wanting to make BLCKSZ runtime configurable within one
> > postgres binary. There's just too much intrinsic overhead associated with
> > that.
>
> How would that work for extensions which may be built for a particular
> BLCKSZ value (like pageinspect)?

I think we'd need to do something similar for extensions, likely loading them
from a path that includes the "subvariant" the server currently is running. Or
alternatively adding a suffix to the filename indicating the
variant. Something like pageinspect.x86-64-v4-4kB.so.

The x86-64-v* stuff is something gcc and clang added a couple years ago, so
that not every project has to define different "baseline" levels. I think it
was done in collaboration with the sytem-v/linux AMD64 ABI specification group
([1]).

Greetings,

Andres

[1] https://gitlab.com/x86-psABIs/x86-64-ABI/-/jobs/artifacts/master/raw/x86-64-ABI/abi.pdf?job=build
section 3.1.1.