Re: [PERFORM] Help with tuning this query (with

Tom Lane wrote:

>"Magnus Hagander" <mha(at)sollentuna(dot)net> writes:
>
>
>>There is. I beleive QueryPerformanceCounter has sub-mirosecond
>>resolution.
>>
>>
>>Can we just replace gettimeofday() with a version that's basically:
>>
>>
>
>No, because it's also used for actual time-of-day calls. It'd be
>necessary to hack executor/instrument.c in particular.
>
> regards, tom lane
>
>
It seems that there are 2 possibilities. Leave gettimeofday as it is,
and then change code that calls it for deltas with a
"pg_get_high_res_delta_time()", which on most platforms is just
gettimeofday, but on win32 is a wrapper for QueryPerformanceCounter().

Or we modify the win32 gettimeofday call to something like:

gettimeofday(struct timeval *tv, struct timezone *tz)
{
static int initialized = 0;
static LARGE_INTEGER freq = {0};
static LARGE_INTEGER base = {0};
static struct time_t base_tm = {0};
LARGE_INTEGER now = {0};
int64_t delta_secs = 0;

if(!initialized) {
QueryPerformanceFrequency(&freq);
base_tm = time(NULL); // This can be any moderately accurate time
function, maybe getlocaltime if it exists
QueryPerformanceCounter(&base);
}

QueryPerformanceCounter(&now);
delta_secs = now.QuadPart - base.QuadPart;
tv->tv_sec = delta_secs / freq.QuadPart;
delta_secs -= *tv.tv_sec * freq.QuadPart;
tv->tv_usec = delta_secs * 1000000 / freq.QuadPart

tv->tv_sec += base_tm;

return 0;
}