Re: Synch Rep: communication between backends and walsender

Hi,

Fujii Masao wrote:
> One of the major complaints about the current synch rep patch is that
> signals are used for communication between backends and walsender.
> On some platforms, a signal doesn't interrupt sleep (i.e. poll or select
> system call), which would increase the performance overhead of
> replication.

Reading the past messages on this topic, I realized that this problem so
far only affects HPUX. I fear the proposed UDP/semaphores approach might
have a similar gotcha on at least one of the supported platforms, too.
Limits of open file descriptors come to mind, for example. Or kernel
packet filtering rules, as mentioned in pgstat.c.

If I understand correctly, even Postgres itself suffers from that
problem on HPUX (even though the consequences aren't dramatic, as
pointed out by Tom). Plus we are not completely save from syscalls
returning EINTR due to SA_RESTART not being set for SIGALRM.

So, does it really make sense to take care of this issue as part of the
sync rep patch?

Regards

Markus Wanner