Re: [HACKERS] Problem after removal of exec(), help

>
> Since the removal of exec(), Thomas has seen, and I have confirmed that
> if a backend crashes, and the postmaster must reset the shared memory,
> no backends can connect anymore.  One way to reproduce it is to run the
> regression tests, which on their last test will crash for an un-related
> reason.  However, it will not allow you to restart any more backends.
>
> The error it gets is:
>
> Failed Assertion("!((((unsigned long)nextElem) > ShmemBase)):", File: "shmqueue.
> c", Line: 83)
> !((((unsigned long)nextElem) > ShmemBase)) (0) [No such file or directory]
>
> In this case nextElem = ShmemBase, so it is not greater.  Removing the
> Assert() still does not make things work, so there must be something
> else.
>
> Now, the problem is probably not at that exact spot, but somewhere
> deeper.  There are two differences between the old non-exec() behavior
> and new behavior.  In the old setup, the backend had all its global
> variables initialized, while in the new no-exec case, they take the
> global variable values from the postmaster.  Second, the old setup had
> each backend attaching to the shared memory, while the new setup has
> them inheriting the shared memory from the fork().

I have fixed the problem.  The problem was that InitMultiLevelLocks()
was not re-initializing the LockTable, which was still pointing to the
old shared memory lock structures, not the new ones in the new shared
memory segment.

I had to change InitMultiLevelLocks so it always reset the memory, and
force LockTableInit to set Numtables in lock.c to 1 on startup, so it
re-creates the LOCKTAB entries that do not point to the old shared
memory stuff.

I also replaces on_exitpg with new on_proc_exit and on_shmem_exit() to
clarify when these are being run, and removed quasi_exit().

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