Re: Millisecond-precision connect_timeout for libpq

On 9 July 2013 18:43, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2013-07-05 21:28:59 +0400, ivan babrou wrote:
>> Hi, guys! I made a quick patch to support floating number in
>> connect_timeout param for libpq. This will treat floating number as
>> seconds so this is backwards-compatible. I don't usually write in C,
>> so there may be mistakes. Could you review it and give me some
>> feedback?
>>
>> --
>> Regards, Ian Babrou
>> http://bobrik.name http://twitter.com/ibobrik skype:i.babrou
>
>> diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
>> index 18fcb0c..58c1a35 100644
>> --- a/src/interfaces/libpq/fe-connect.c
>> +++ b/src/interfaces/libpq/fe-connect.c
>> @@ -1452,7 +1452,7 @@ static int
>> connectDBComplete(PGconn *conn)
>> {
>> PostgresPollingStatusType flag = PGRES_POLLING_WRITING;
>> - time_t finish_time = ((time_t) -1);
>> + struct timeval finish_time;
>>
>> if (conn == NULL || conn->status == CONNECTION_BAD)
>> return 0;
>> @@ -1462,17 +1462,14 @@ connectDBComplete(PGconn *conn)
>> */
>> if (conn->connect_timeout != NULL)
>> {
>> - int timeout = atoi(conn->connect_timeout);
>> + int timeout_usec = (int) (atof(conn->connect_timeout) * 1000000);
>
> I'd rather not use a plain int for storing usecs. An overflow is rather
> unlikely, but still. Also, I'd rather use something like USECS_PER_SEC
> instead of a plain 1000000 in multiple places.
>
>>
>> - if (timeout > 0)
>> + if (timeout_usec > 0)
>> {
>> - /*
>> - * Rounding could cause connection to fail; need at least 2 secs
>> - */
>> - if (timeout < 2)
>> - timeout = 2;
>> - /* calculate the finish time based on start + timeout */
>> - finish_time = time(NULL) + timeout;
>> + gettimeofday(&finish_time, NULL);
>> + finish_time.tv_usec += (int) timeout_usec;
>
> Accordingly adjust this.
>
> Looks like a sensible thing to me.
>
> *Independent* from this patch, you might want look into server-side
> connection pooling using transaction mode. If that's applicable for
> your application it might reduce latency noticeably.
>
> Greetings,
>
> Andres Freund
>
> --
> Andres Freund http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services

I tried to make it more safe. Still not sure about constants, I
haven't found any good examples in libpq.

--
Regards, Ian Babrou
http://bobrik.name http://twitter.com/ibobrik skype:i.babrou