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().
>
> My guess is that there is something buggy about the reset code in
> postmaster.c that was not resetting completely, but the initialization
> of the global variables in the backend was masking the bug, or the
> attach() operation did some extra work that we now need to do when
> resetting the shared memory:
>
> static void
> reset_shared(short port)
> {
> ipc_key = port * 1000 + shmem_seq * 100;
> CreateSharedMemoryAndSemaphores(ipc_key);
> ActiveBackends = FALSE;
> shmem_seq += 1;
> if (shmem_seq >= 10)
> shmem_seq -= 10;
> }
>
>
> I am stumped on this.

No help here, but a request:

Could we have an option to do the fork()/exec() the old way as well as the
new sleek fork() only. I want to do some performance testing under gprof and
want to be able to replace my postgres binary with a shell script to save
the gmon.out file eg:

#!/bin/sh
postgres.bin $*
mv gmon.out gmon.$$

This won't work unless and exec() is done.

-dg

David Gould dg(at)illustra(dot)com 510.628.3783 or 510.305.9468
Informix Software (No, really) 300 Lakeside Drive Oakland, CA 94612
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good, you'll have to ram them down people's throats." -- Howard Aiken