Hi,
On Thu, Nov 14, 2024 at 11:35:25AM -0500, Peter Geoghegan wrote:
> On Thu, Nov 14, 2024 at 11:29 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > ISTM that we have spare bytes where we could place that boolean without
> > breaking ABI. In x86_64 there's a couple of 4-byte holes, but those
> > won't be there on x86, so not great candidates. Fortunately there are
> > 3-byte and 7-byte holes also, which we can use safely. We can move the
> > new boolean to those location.
>
> Wasn't this part of the official guidelines?
Do you mean in [1] (Maintaining ABI compatibility while backpatching section)?
If so, it looks like it's not currently mentioned.
What about?
"
You cannot modify any struct definition in src/include/*. If any new members must
be added to a struct, put them in the padding holes (if any) in backbranches (or
at the end of the struct if there is no padding holes available).
"
Also we may need a decision table to ensure 32-bit portability based on the
hole size on 64-bit, something like?
64-bit hole size | use on 32-bit?
-----------------|---------------
<=3 bytes | safe to use
4 bytes | don't use
5-7 bytes | use first (hole_size - 4) bytes only
Does that make sense?
Regards,
[1]: https://wiki.postgresql.org/wiki/Committing_checklist
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
