Horton

Re: [HACKERS] Weaker shmem interlock w/o postmaster.pid

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Daniel Gustafsson <daniel@yesql.se>
Cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>, "9erthalion6@gmail.com" <9erthalion6@gmail.com>, "sfrost@snowman.net" <sfrost@snowman.net>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2019-03-31T22:42:33Z
Lists: pgsql-hackers 
On Fri, Mar 29, 2019 at 09:53:51AM +0000, Daniel Gustafsson wrote:
> On Saturday, March 9, 2019 8:16 AM, Noah Misch <noah@leadboat.com> wrote:
> > I renamed IpcMemoryAnalyze() to PGSharedMemoryAttach() and deleted the old
> > function of that name. Now, this function never calls shmdt(); the caller is
> > responsible for that. I do like things better this way. What do you think?
> 
> I think it makes for a good API for the caller to be responsible, but it does
> warrant a comment on the function to explicitly state that.

The name "PGSharedMemoryAttach" makes that fact sufficiently obvious, I think.

> A few other small comments:
> 
> +   state = PGSharedMemoryAttach((IpcMemoryId) id2, &memAddress);
> +   if (memAddress)
> +       shmdt(memAddress);
> 
> This seems like a case where it would be useful to log a shmdt() error or do
> an Assert() around the success of the operation perhaps?

I'll add the same elog(LOG) we have at other shmdt() sites.  I can't think of
a site where we Assert() about the results of a system call.  While shmdt()
might be a justified exception, elog(LOG) seems reasonable.

> +    * Loop till we find a free IPC key.  Trust CreateDataDirLockFile() to
> +    * ensure no more than one postmaster per data directory can enter this
> +    * loop simultaneously.  (CreateDataDirLockFile() does not ensure that,
> +    * but prefer fixing it over coping here.)
> 
> This comment make it seem like there is a fix to CreateLockFile() missing to
> his patch, is that correct? If so, do you have an idea for that patch?

That comment refers to
https://postgr.es/m/flat/20120803145635.GE9683%40tornado.leadboat.com

> Switching this to Ready for Committer since I can't see anything but tiny things.

Thanks.

Commits

  1. Probe only 127.0.0.1 when looking for ports on Unix.

  2. Don't write to stdin of a test process that could have already exited.

  3. Test both 0.0.0.0 and 127.0.0.x addresses to find a usable port.

  4. MSYS: Translate REGRESS_SHLIB to a Windows file name.

  5. MSYS: Skip src/test/recovery/t/017_shm.pl.

  6. When Perl "kill(9, ...)" fails, try "pg_ctl kill".

  7. Consistently test for in-use shared memory.

  8. Revert "Consistently test for in-use shared memory."

  9. Silence -Wimplicit-fallthrough in sysv_shmem.c.

  10. Make src/test/recovery/t/017_shm.pl safe for concurrent execution.

  11. Update HINT for pre-existing shared memory block.

  12. Add WL_EXIT_ON_PM_DEATH pseudo-event.

  13. The default values for shared_buffers and max_connections are now 1000

  14. XLOG (and related) changes:

  15. Significant cleanups in SysV IPC handling (shared mem and semaphores).