Re: Synchronous Log Shipping Replication

On Wed, Sep 10, 2008 at 11:13 PM, Markus Wanner <markus(at)bluegap(dot)ch> wrote:
>> Which signal should we use for the notification to the backend from
>> WAL sender? The notable signals are already used.
>
> I'm using SIGUSR1, see src/backend/storage/ipc/imsg.c from Postgres-R, line
> 232. That isn't is use for backends or the postmaster, AFAIK.

Umm... backends have already used SIGUSR1. PostgresMain() sets up a signal
handler for SIGUSR1 as follows.

pqsignal(SIGUSR1, CatchupInterruptHandler);

Which signal should WAL sender send to backends?

>> Or, since a backend don't need to wait on select() unlike WAL sender,
>> ISTM that it's not so inconvenient to use a semaphore for that
>> notification.
>
> They probably could, but not the WAL sender.

Yes, since WAL sender waits on select(), it's convenient to use signal
for the notification *from backends to WAL sender*, I think too.

Best regards,

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