On Thu, Jun 9, 2016 at 12:56 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Thom Brown <thom@linux.com> writes:
>> On 15 May 2014 at 19:56, Bruce Momjian <bruce@momjian.us> wrote:
>>> On Tue, May 13, 2014 at 06:58:11PM -0400, Tom Lane wrote:
>>>> A recent question from Tim Kane prompted me to measure the overhead
>>>> costs of EXPLAIN ANALYZE, which I'd not checked in awhile. Things
>>>> are far worse than I thought. On my current server (by no means
>>>> lavish hardware: Xeon E5-2609 @2.40GHz) a simple seqscan can run
>>>> at something like 110 nsec per row:
>
>> Did this idea die, or is it still worth considering?
>
> We still have a problem, for sure. I'm not sure that there was any
> consensus on what to do about it. Using clock_gettime(CLOCK_REALTIME)
> if available would be a straightforward change that should ameliorate
> gettimeofday()'s 1-usec-precision-limit problem; but it doesn't do
> anything to fix the excessive-overhead problem. The ideas about the
> latter were all over the map, and none of them looked easy.
>
> If you're feeling motivated to work on this area, feel free.
How about using both CLOCK_REALTIME and CLOCK_REALTIME_COARSE
as the clock id's in clock_gettime wherever applicable. COARSE option is used
wherever there is no timing calculation is required, because in my laptop, there
is a significant performance difference is observed (like 8 times) compared to
CLOCK_REALTIME.
If it is fine, I will try to update the code and send a patch.
Regards,
Hari Babu
Fujitsu Australia
