Re: Crash during backend start when low on memory

Hi,

On 2023-02-05 22:00:20 +0100, Mats Kindahl wrote:
> Tom had some concerns about using PG_TRY() inside the postmaster
> ServerLoop

I don't think we gain anything in most of the places by using PG_TRY
instead of a non-throwing allocations. The relevant is cooperating
closely enough that just returning returning a failure indicator is
sufficient.

Note that that doesn't mean that palloc can't be used, see
MCXT_ALLOC_NO_OOM.

>, but I cannot see how that can cause problems since it is "just"
> a setjmp() and longjmp(). It allocates a structure on the stack that
> contains the values of the registers and the signal set; it is big, but not
> exceedingly so. If somebody could enlighten me about if there are any
> problems with this, I would be very grateful.

If you aren't careful you end up with PG_exception_stack in a backend
still pointing to that PG_TRY. Which means that an error during backend
startup would jump into postmaster code. Which would not be good.

Particularly because this is a bugfix we need to make the fix more
minimal than the patches proposed so far.

Greetings,

Andres Freund