On 10/03/2014 05:26 PM, Andres Freund wrote:
On 2014-10-03 17:12:18 +0300, Heikki Linnakangas wrote:
On 09/28/2014 01:54 AM, Andres Freund wrote:
0003 Sinval/notify processing got simplified further. There really isn't
      any need for DisableNotifyInterrupt/DisableCatchupInterrupt
      anymore. Also begin_client_read/client_read_ended don't make much
      sense anymore. Instead introduce ProcessClientReadInterrupt (which
      wants a better name).
There's also a very WIP
0004 Allows secure_read/write be interrupted when ProcDiePending is
      set. All of that happens via the latch mechanism, nothing happens
      inside signal handlers. So I do think it's quite an improvement
      over what's been discussed in this thread.
      But it (and the other approaches) do noticeably increase the
      likelihood of clients not getting the error message if the client
      isn't actually dead. The likelihood of write() being blocked
      *temporarily* due to normal bandwidth constraints is quite high
      when you consider COPY FROM and similar. Right now we'll wait till
      we can put the error message into the socket afaics.

1-3 need some serious comment work, but I think the approach is
basically sound. I'm much, much less sure about allowing send() to be

Yeah, 1-3 seem sane.

I think 3 also needs a careful look. Have you looked through it? While
imo much less complex than before, there's some complex interactions in
the touched code. And we have terrible coverage of both catchup
interrupts and notify stuff...

I only looked at the .patch, I didn't apply it, so I didn't look at the context much. But I don't see any fundamental problem with it. I would like to have a closer look before it's committed, though.

There's also the concern that using a latch for client communication
increases the number of syscalls for the same work. We should at least
try to quantify that...

I'm not too concerned about that, since we only do extra syscalls when the socket isn't immediately available for reading/writing, i.e. when we have to sleep anyway.

4 also looks OK to me at a quick glance. It basically
enables handling the "die" interrupt immediately, if we're blocked in a read
or write. It won't be handled in the signal handler, but within the
secure_read/write call anyway.

What are you thinking about the concern that it'll reduce the likelihood
of transferring the error message to the client? I tried to reduce that
by only allowing errors when write() blocks, but that's not an
infrequent event.

I'm not too concerned about that either. I mean, it's probably true that it reduces the likelihood, but I don't particularly care myself. But if we care, we could use a timeout there, so that if we receive a SIGTERM while blocked on a send(), we wait for a few seconds to see if we can send whatever we were sending, before terminating the backend.

What should we do with this patch in the commitfest? Are you planning to clean up and commit these patches?

- Heikki

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