Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > FYI, the shared memory address was originally relocatable by using > > offsets to address it from the child, but now that we use fork() on > > Unix, it isn't an issue, and Win32 seems to be OK. > > In the worst case we could go back to using offsets everywhere, but I'm > really reluctant to do that for reasons of code clarity and reliability. > The main problem with it is that you have to explicitly cast to and from > the correct pointer type, which is not only ugly but completely defeats > any chance of the compiler catching wrong-type errors.
As I remember, the offsets also had a performance and/or storage impact we don't want either. > What I am seeing on Fedora 4 (I suppose it's common to most recent Linux > versions) is that the system preferentially maps the shared memory > segment just below the stack, which is good from the point of view of > preserving maximum address space for the heap, but not so great if stack > size changes or the stack moves a bit. It'd be possible to get a little > more flexibility by requesting a non-default attach location for the > postmaster's initial shmat call. I'm not interested in getting into > that if we don't absolutely have to, but it might be the best answer if > we find ourselves seeing similar issues on specific platforms (ie > Windows) in the future. Agreed. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
