On Sun, 2023-11-12 at 21:55 -0500, Tom Lane wrote:
> yuansong <yyuansong@126.com> writes:
> > In PostgreSQL, when a backend process crashes, it can cause other backend
> > processes to also require a restart, primarily to ensure data consistency.
> > I understand that the correct approach is to analyze and identify the
> > cause of the crash and resolve it. However, it is also important to be
> > able to handle a backend process crash without affecting the operation of
> > other processes, thus minimizing the scope of negative impact and
> > improving availability. To achieve this goal, could we mimic the Oracle
> > process by introducing a "pmon" process dedicated to rolling back crashed
> > process transactions and performing resource cleanup? I wonder if anyone
> > has attempted such a strategy or if there have been previous discussions
> > on this topic.
>
> The reason we force a database-wide restart is that there's no way to
> be certain that the crashed process didn't corrupt anything in shared
> memory. (Even with the forced restart, there's a window where bad
> data could reach disk before we kill off the other processes that
> might write it. But at least it's a short window.) "Corruption"
> here doesn't just involve bad data placed into disk buffers; more
> often it's things like unreleased locks, which would block other
> processes indefinitely.
>
> I seriously doubt that anything like what you're describing
> could be made reliable enough to be acceptable. "Oracle does
> it like this" isn't a counter-argument: they have a much different
> (and non-extensible) architecture, and they also have an army of
> programmers to deal with minutiae like undoing resource acquisition.
> Even with that, you'd have to wonder about the number of bugs
> existing in such necessarily-poorly-tested code paths.
Yes.
I think that PostgreSQL's approach is superior: rather than investing in
code to mitigate the impact of data corruption caused by a crash, invest
in quality code that doesn't crash in the first place.
Euphemistically naming a crash "ORA-600 error" seems to be part of
their strategy.
Yours,
Laurenz Albe
