Horton

Re: Refactoring backend fork+exec code

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Andres Freund <andres@anarazel.de>, Tristan Partin <tristan@neon.tech>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2024-01-10T12:35:52Z
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 08/12/2023 14:33, Heikki Linnakangas wrote:
>>> +	[PMC_AV_LAUNCHER] = {"autovacuum launcher", AutoVacLauncherMain, true},
>>> +	[PMC_AV_WORKER] = {"autovacuum worker", AutoVacWorkerMain, true},
>>> +	[PMC_BGWORKER] = {"bgworker", BackgroundWorkerMain, true},
>>> +	[PMC_SYSLOGGER] = {"syslogger", SysLoggerMain, false},
>>> +
>>> +	[PMC_STARTUP] = {"startup", StartupProcessMain, true},
>>> +	[PMC_BGWRITER] = {"bgwriter", BackgroundWriterMain, true},
>>> +	[PMC_ARCHIVER] = {"archiver", PgArchiverMain, true},
>>> +	[PMC_CHECKPOINTER] = {"checkpointer", CheckpointerMain, true},
>>> +	[PMC_WAL_WRITER] = {"wal_writer", WalWriterMain, true},
>>> +	[PMC_WAL_RECEIVER] = {"wal_receiver", WalReceiverMain, true},
>>> +};
>>
>> It feels like we have too many different ways of documenting the type of a
>> process. This new PMC_ stuff, enum AuxProcType, enum BackendType.
> Agreed. And "am_walsender" and such variables.

Here's a patch that gets rid of AuxProcType. It's independent of the 
other patches in this thread; if this is committed, I'll rebase the rest 
of the patches over this and get rid of the new PMC_* enum.

Three patches, actually. The first one fixes an existing comment that I 
noticed to be incorrect while working on this. I'll push that soon, 
barring objections. The second one gets rid of AuxProcType, and the 
third one replaces IsBackgroundWorker, IsAutoVacuumLauncherProcess() and 
IsAutoVacuumWorkerProcess() with checks on MyBackendType. So 
MyBackendType is now the primary way to check what kind of a process the 
current process is.

'am_walsender' would also be fairly straightforward to remove and 
replace with AmWalSenderProcess(). I didn't do that because we also have 
am_db_walsender and am_cascading_walsender which cannot be directly 
replaced with MyBackendType. Given that, it might be best to keep 
am_walsender for symmetry.

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