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Re: Fwd: 8.0 Beta3 worked, RC1 didn't!

From: Gary Doades <gpd(at)gpdnet(dot)co(dot)uk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers-win32(at)postgresql(dot)org
Subject: Re: Fwd: 8.0 Beta3 worked, RC1 didn't!
Date: 2004-12-24 16:15:30
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers-win32
Tom Lane wrote:
> Gary Doades <gpd(at)gpdnet(dot)co(dot)uk> writes:
>>AFAIK Win32 does not care where in private process address space the 
>>"shared memory" segment is. It can be mapped to different addresses in 
>>different processes and still share the same physical address space. 
>>This is why Win32 puts the private shared address anywhere in its own 
>>address space, because it doesn't matter.
> Win32 may not care, but we do.  The shared memory segment must be mapped
> at the same address in every backend.

Forgive me for not knowing the internals of postgres, but why? As long 
as all the shared memory is accessed from the same relative offsets from 
the private starting address it will refer to the same physical shared 
memory address and should work.

Is this to maintain compatibility with the other platforms way of doing 
things, or the postgres internal architecture?

If this is the case then your suggestion may be the only one, to 
artificially bump up the first free address and hope that it is enough. 
Seems a bit hit and miss though (probably more hit than miss) since it's 
not easily known what the extra allocation for the subsequent backends 
may be.

>>If you try to force it to any particular private process address you may 
>>fail as you don't always know where program code (DLLs etc.) may be loaded.
> This is (or ought to be) irrelevant, because we are only talking about
> instances of a single executable.
Agreed, as long as you can't have code dynamically linked from one 
backend, but not another.


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