Re: BUG #9118: WAL Sender does not disconnect replication clients during shutdown

On Fri, Mar 14, 2014 at 12:22 PM, Michael Paquier
<michael.paquier@gmail.com> wrote:
> On Fri, Mar 14, 2014 at 3:59 AM, Fujii Masao <masao.fujii@gmail.com> wrote:
>> On second thought, I think that it's better to check a write location instead
>> if walsender is connecting to a standby such as pg_receivexlog which
>> always returns an invalid flush location. Attached patch does this. Thought?
> Just a small one: could it be possible to put the condition checking
> for the validity of flush/write position into a separate variable out
> of this if() for readability?
> sentPtr == MyWalSnd->flush ||
> !          (XLogRecPtrIsInvalid(MyWalSnd->flush) &&
> !           sentPtr == MyWalSnd->write)

Yes, that's possible. What about the attached patch?

> Are there risks that a standby sends an invalid flush location and a
> valid write location?

No unless I'm missing something.

        /*
         * We only send regular messages to the client for full decoded
         * transactions, but a synchronous replication and walsender shutdown
         * possibly are waiting for a later location. So we send pings
         * containing the flush location every now and then.
         */
        if (MyWalSnd->flush < sentPtr && !waiting_for_ping_response)
        {

BTW, ISTM that the above condition in walsender.c has the same problem.
If the standby is pg_receivexlog, MyWalSnd->flush is always an invalid
location and that condition would always be TRUE. We would need the
same fix also there.

Regards,

--
Fujii Masao