Re: [PATCH] Magic block for modules

On Sun, May 07, 2006 at 08:21:43PM -0400, Tom Lane wrote:
> > changes in any of the following:
>
> > PG_VERSION_NUM
> > CATALOG_VERSION_NO
> > the size of 8 basic C types
> > BLCKSZ=20
> > NAMEDATALEN=20
> > HAVE_INT64_TIMESTAMP
> > INDEX_MAX_KEYS
> > FUNC_MAX_ARGS
> > VARHDRSZ
> > MAXDIM
> > The compiler used (only brand, not version)
>
> That seems way overkill to me. FUNC_MAX_ARGS is good to check, but
> most of those other things are noncritical for typical add-on modules.

I was trying to find variables that when changed would make some things
corrupt. For example, a changed NAMEDATALEN will make any use of the
syscache a source of errors. A change in INDEX_MAX_KEYS will break the
GiST interface, etc. I wondered about letting module writers to select
which parts are relevent to them but that just seems like handing
people a footgun.

> In particular I strongly object to the check on compiler. Some of us do
> use systems where gcc and vendor compilers are supposed to interoperate
> ... and aren't all those Windows compilers supposed to, too? AFAIK

Maybe that's the case now, it didn't used to be. I seem to remember
people having difficulties because they compiled the server with MinGW
and the modules with VC++. I'll take it out though, it's not like it
costs anything.

> it's considered the linker's job to prevent loading 32-bit code into
> a 64-bit executable or vice versa, so I don't think we need to be
> checking for common assumptions about sizeof(long).

I know ELF headers contain some of this info, and unix in general
doesn't try to allow different bit sizes in one binary. Windows used to
(maybe still has) a mechanism to allow 32-bit code to call 16-bit
libraries. Do they allow the same for 64-bit libs?

> I'm pretty sure we had agreed that magic blocks should be required;
> otherwise this check will accomplish little.

Sure, I just didn't want to break every module in one weekend. I was
thinking of adding it with LOG level now, send a message on -announce
saying that at the beginning of the 8.2 freeze it will be an ERROR.
Give people time to react.

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.