Background Processes in Postgres Extension

Sushrut Shivaswamy <sushrut.shivaswamy@gmail.com> writes:

I'm developing a postgres extension as a custom Table Interface method
definition.
WIthin the extension, I"m planning to create two background processes using
`fork()` that will process data in the background.

Are there any recommendations / guidelines around creating background
processes within extensions in postgres?

fork() is entirely the wrong way to do it, mainly because when the
creating session exits the postmaster will be unaware of those
now-disconnected child processes. See the mechanisms for creating
background worker processes (start with bgworker.h).

regards, tom lane

Thanks for the suggestion on using postgres background worker.

I tried creating one following the implementation in worker_spi and am able
to spawn a background worker successfully.

However, the background worker seems to cause postmaster to crash when I
wait for it to finish using `WaitForBackgroundWorkerShutdown.
The function called by the background worker is empty except for logging a
message to disk.

Any ideas on what could be going wrong / tips for debugging?

Thanks,
Sushrut

On Sat, Apr 27, 2024 at 9:26 PM Sushrut Shivaswamy <
sushrut.shivaswamy@gmail.com> wrote:

Thanks for the suggestion on using postgres background worker.

I tried creating one following the implementation in worker_spi and am
able to spawn a background worker successfully.

However, the background worker seems to cause postmaster to crash when I
wait for it to finish using `WaitForBackgroundWorkerShutdown.
The function called by the background worker is empty except for logging a
message to disk.

When debugging a crash, backtrace from core dump is useful. if you can
reproduce the crash, running reproduction with gdb attached to a process
intended to crash is more useful.

--
Best Wishes,
Ashutosh Bapat