Re: Multiplexing SUGUSR1

Hi,

On Wed, Dec 10, 2008 at 1:43 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Heikki Linnakangas <heikki.linnakangas@enterprisedb.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?

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center