Thread

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

Goran Thyni <goran@bildbasen.se> — 1998-06-23T11:11:26Z

Bruce Momjian wrote:
> 
> 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().

Bruce,
I have not look into it the specifics yet,
but I suggest looking into what is done when
the child process exits.
This (the pg_exit() et al.) caused some bugs
when we introduced unix domain sockets and
it is not the first place one looks. :-(

	regards,
-- 
---------------------------------------------
Göran Thyni, sysadm, JMS Bildbasen, Kiruna