Re: timeout of pg_receivexlog --status-interval

On Tue, Jul 15, 2014 at 7:38 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
> On Thu, Jul 10, 2014 at 11:10 PM, Sawada Masahiko <sawada.mshk@gmail.com> wrote:
>> Hi,
>>
>> At 1047 line of receivelog.c:CopyStreamPoll(), we set NULL to
>> timeoutptr variable.
>> if the value of timeoutprt is set NULL then the process will wait
>> until can read socket using by select() function as following.
>>
>>     if (timeout_ms < 0)
>>         timeoutptr = NULL;
>>     else
>>     {
>>         timeout.tv_sec = timeout_ms / 1000L;
>> timeout.tv_usec = (timeout_ms % 1000L) * 1000L;
>>         timeoutptr = &timeout;
>>     }
>>
>>     ret = select(PQsocket(conn) + 1, &input_mask, NULL, NULL, timeoutptr);
>>
>> But the 1047 line of receivelog.c is never executed because the value
>> of timeout_ms is NOT allowed less than 0 at CopyStreamReceive which is
>> only one function calls CopyStreamPoll().
>> The currently code, if we specify -s to 0 then CopyStreamPoll()
>> function is never called.
>> And the pg_receivexlog will be execute PQgetCopyData() and failed, in
>> succession.
>
> Thanks for reporting this! Yep, this is a problem.
>
>> I think that it is contradiction, and should execute select() function
>> with NULL of fourth argument.
>> the attached patch allows to execute select() with NULL, i.g.,
>> pg_receivexlog.c will wait until can  read socket without timeout, if
>> -s is specified to 0.
>
> Your patch changed the code so that CopyStreamPoll is called even
> when the timeout is 0. I don't agree with this change because the
> timeout=0 basically means that the caller doesn't request to block and
> there is no need to call CopyStreamPoll in this case. So I'm thinking to
> apply the attached patch. Thought?
>

Thank you for the response.
I think this is  better.

One another point about select() function, I think that they are same
behavior between the fifth argument is NULL and 0(i.g. 0 sec).
so I think that it's better to change the CopyStreamPoll() as followings.

@@ -1043,7 +1043,7 @@ CopyStreamPoll(PGconn *conn, long timeout_ms)       FD_ZERO(&input_mask);
FD_SET(PQsocket(conn),&input_mask);
 

-       if (timeout_ms < 0)
+       if (timeout_ms <= 0)               timeoutptr = NULL;       else       {

Please give me feed back.

Regards,

-------
Sawada Masahiko