Horton

Re: Refactoring backend fork+exec code

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: reid.thompson@crunchydata.com, Andres Freund <andres@anarazel.de>
Cc: Tristan Partin <tristan@neon.tech>, pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2024-01-30T00:08:36Z
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.

Attachments

On 29/01/2024 17:54, reid.thompson@crunchydata.com wrote:
> On Thu, 2024-01-25 at 01:51 +0200, Heikki Linnakangas wrote:
>>
>> And here we go. BackendID is now a 1-based index directly into the
>> PGPROC array.
> 
> Would it be worthwhile to also note in this comment FIRST_AUX_PROC's
> and IsAuxProcess()'s dependency on B_ARCHIVER and it's location in the
> enum table?

Yeah, that might be in order. Although looking closer, it's only used in 
IsAuxProcess, which is only used in one sanity check in 
AuxProcessMain(). And even that gets refactored away by the later 
patches in this thread. So on second thoughts, I'll just remove it 
altogether.

I spent some more time on the 'lastBackend' optimization in sinvaladt.c. 
I realized that it became very useless with these patches, because aux 
processes are allocated pgprocno's after all the slots for regular 
backends. There are always aux processes running, so lastBackend would 
always have a value close to the max anyway. I replaced that with a 
dense 'pgprocnos' array that keeps track of the exact slots that are in 
use. I'm not 100% sure this is worth the effort; does any real world 
workload send shared invalidations so frequently that this matters? In 
any case, this should avoid the regression if such a workload exists.

New patch set attached. I think these are ready to be committed, but 
would appreciate a final review.

-- 
Heikki Linnakangas
Neon (https://neon.tech)