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

From: John A Meinel <john(at)arbash-meinel(dot)com>
To: Dave Held <dave(dot)held(at)arrayservicesgrp(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org,pgsql-hackers-win32(at)postgresql(dot)org
Subject: Re: [PERFORM] Help with tuning this query (with
Date: 2005-03-07 22:48:10
Message-ID: 422CDA2A.1000105@arbash-meinel.com (view raw or flat)
Thread:
Lists: pgsql-hackers-win32pgsql-performance
Dave Held wrote:

>There is always clock().  It's mandated by ANSI C, but my docs say
>that POSIX requires CLOCKS_PER_SEC == 1000000 regardless of actual
>timer resolution, which seems a little brain-dead to me.
>
>__
>David B. Held
>  
>

My experience with clock() on win32 is that CLOCKS_PER_SEC was 1000, and 
it had a resolution of 55clocks / s. When I just did this:

int main(int argc, char **argv)
{
    int start = clock();
    int now = start;
    cout << "Clock: " << CLOCKS_PER_SEC << endl;
    for(int i = 0; i < 10; ++i) {
        while(now == clock()) {
            // Do nothing
        }
        now = clock();
        cout << now-start << "\t" << (now - start) / (double) 
CLOCKS_PER_SEC << endl;
    }
}

I got:
Clock: 1000
16      0.016
31      0.031
47      0.047
62      0.062
78      0.078
93      0.093
109     0.109
125     0.125
141     0.141
156     0.156

Which is about 1/0.016 = 62.5 clocks per second.
I'm pretty sure this is slightly worse than what we want. :)
It might be better on other platforms, but on win32 clock() is most 
definitely *not* what you want.
John
=:->

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