Re: BUG #15804: Assertion failure when using logging_collector with EXEC_BACKEND

I wrote:
> It might be better to give up the assertion in PGSharedMemoryNoReAttach,
> and just make it work more like PGSharedMemoryDetach, ie "detach if
> UsedShmemSegAddr is set, else do nothing". I don't remember for sure,
> but if we do that, there might be no functional difference anymore
> between those two functions, in which case we might as well merge 'em.

Apropos of this: I notice that commit 57431a911 is already relying
on PGSharedMemoryDetach to do the "right thing" here, because that
gets called in the non-EXEC_BACKEND code path, cf SysLogger_Start:

/* Drop our connection to postmaster's shared memory, as well */
dsm_detach_all();
PGSharedMemoryDetach();

I'm also not too happy that this comment doesn't mention the fact that
we'd (now) only be attached to shmem in the case of a postmaster restart.

BTW, it looks to me like dsm_detach_all doesn't get called anywhere in
the EXEC_BACKEND case, which seems like a separate bug.

regards, tom lane