Horton

Re: Refactoring backend fork+exec code

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Tristan Partin <tristan@neon.tech>, pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2023-12-01T01:42:44Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid 0-length memcpy to NULL with EXEC_BACKEND

  2. Tighten check for --forkchild argument when spawning child process

  3. Add missing PGDLLIMPORT markings

  4. Remove assertions that some compiler say are tautological

  5. Move code for backend startup to separate file

  6. Refactor postmaster child process launching

  7. Move some functions from postmaster.c to a new source file

  8. Split registration of Win32 deadchild callback to separate function

  9. Improve log messages referring to background worker processes

  10. Move initialization of the Port struct to the child process

  11. Pass CAC as an argument to the backend process

  12. Set socket options in child process after forking

  13. Fix references to renamed function in comments

  14. Use MyBackendType in more places to check what process this is

  15. Remove MyAuxProcType, use MyBackendType instead

  16. Replace BackendIds with 0-based ProcNumbers

  17. Redefine backend ID to be an index into the proc array

  18. Remove superfluous 'pgprocno' field from PGPROC

  19. Fix incorrect comment on how BackendStatusArray is indexed

  20. Refactor how InitProcess is called

  21. Pass BackgroundWorker entry in the parameter file in EXEC_BACKEND mode

  22. Refactor CreateSharedMemoryAndSemaphores

  23. Silence Valgrind complaint with EXEC_BACKEND

  24. Adjust obsolete comment explaining set_stack_base().

  25. Print lwlock stats also for aux processes, when built with LWLOCK_STATS

  26. Move canAcceptConnections check from ProcessStartupPacket to caller.

  27. Fix crash on syslogger startup

  28. Refactor ListenSocket array.

  29. Use FD_CLOEXEC on ListenSockets

  30. Don't leak descriptors into subprograms.

  31. Use WaitEventSet API for postmaster's event loop.

  32. Rearrange postmaster's startup sequence for better syslogger results.

  33. Fix and enhance the assertion of no palloc's in a critical section.

Hi,

On 2023-12-01 01:36:13 +0200, Heikki Linnakangas wrote:
> On 30/11/2023 22:26, Andres Freund wrote:
> > On 2023-11-30 01:36:25 +0200, Heikki Linnakangas wrote:
> > >  From a96b6e92fdeaa947bf32774c425419b8f987b8e2 Mon Sep 17 00:00:00 2001
> > > From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
> > > Date: Thu, 30 Nov 2023 00:01:25 +0200
> > > Subject: [PATCH v3 1/7] Refactor CreateSharedMemoryAndSemaphores
> > >
> > > For clarity, have separate functions for *creating* the shared memory
> > > and semaphores at postmaster or single-user backend startup, and
> > > for *attaching* to existing shared memory structures in EXEC_BACKEND
> > > case. CreateSharedMemoryAndSemaphores() is now called only at
> > > postmaster startup, and a new AttachSharedMemoryStructs() function is
> > > called at backend startup in EXEC_BACKEND mode.
> >
> > I assume CreateSharedMemoryAndSemaphores() is still called during crash
> > restart?
>
> Yes.
>
> >  I wonder if it shouldn't split three ways:
> > 1) create
> > 2) initialize
> > 3) attach
>
> Why? What would be the difference between create and initialize phases?

Mainly because I somehow mis-remembered how we deal with the shared memory
allocation when crashing. I somehow had remembered that we reused the same
allocation across restarts, but reinitialized it from scratch. There's a
kernel of truth to that, because we can end up re-attaching to an existing
sysv shared memory segment. But not more. Perhaps I was confusing things with
the listen sockets?

Andres