Re: Let's make PostgreSQL multi-threaded

On Mon, Jun 5, 2023 at 09:30:28PM +0300, Heikki Linnakangas wrote:
> If one process writes over shared memory that it shouldn't, it can cause a
> crash in that process or some other process that reads it. Same with
> multiple threads, no difference there.
>
> With a single process, one thread can modify another thread's "backend
> private" memory, and cause the other thread to crash. Perhaps that's what
> you meant?
>
> In practice, I don't think it's so bad. Even in a multi-threaded
> environment, common bugs like buffer overflows and use-after-free are still
> much more likely to access memory owned by the same thread, thanks to how
> memory allocators work. And a completely random memory access is still more
> likely to cause a segfault than corrupting another thread's memory. And
> tools like CLOBBER_FREED_MEMORY/MEMORY_CONTEXT_CHECKING and valgrind are
> pretty good at catching memory access bugs at development time, whether it's
> multiple processes or threads.

I remember we used to have macros we called before we modified critical
parts of shared memory, and if a process exited while in those blocks,
the server would restart. Unfortunately, I can't find that in the code
now.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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