Re: Multiplexing SUGUSR1

Fujii Masao wrote:
> Hi,
>
> On Wed, Dec 10, 2008 at 1:43 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>>> I'm surprised you feel that way. You suggested earlier
>>> (http://archives.postgresql.org/message-id/28487.1221147665@sss.pgh.pa.us)
>>> that a solution that only works for processes attached to shared memory
>>> would probably suffice for now.
>> Well, I wasn't complaining about the dependence on being attached to
>> shared memory. What I'm complaining about is the dependence on the
>> rather complex PGPROC data structure.
>>
>>> That seems hard, considering that we also want it to work without
>>> locking. Hmm, I presume we can use spinlocks in a signal handler?
>>> Perhaps some sort of a hash table protected by a spinlock would work.
>> No, locks are right out if the postmaster is supposed to be able to use
>> it. What I was thinking of is a simple linear array of PIDs and
>> sig_atomic_t flags. The slots could be assigned on the basis of
>> backendid, but callers trying to send a signal would have to scan the
>> array looking for the matching PID. (This doesn't seem outlandishly
>> expensive considering that one is about to do a kernel call anyway.
>> You might be able to save a few cycles by having the PID array separate
>> from the flag array, which should improve the cache friendliness of the
>> scan.) Also, for those callers who do have access to a PGPROC, there
>> could be a separate entry point that passes backendid instead of PID to
>> eliminate the search.
>
> Thanks for the comment!
> I updated the patch so. Is this patch ready to apply?

On closer look, I don't see anything setting ProcSignalData.pid field.
Which make me believe that the patch can't possibly work.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com