Alex Pinsker

Tuesday, February 23, 2010

Probability to observe the same number calling Random.Rand()

It’s not an efficient query. Just a game…

for (int j = 1; j < 8; j++)
{
    int numElements = (int)Math.Pow(10, j);
    var numersList = Enumerable.Repeat(0, numElements).Select(
        i => Convert.ToDouble(random.Next()))
        .Distinct().OrderBy(i => i);
    double probabilityGetSameNumber = 1 - (double) numersList.Count()/numElements;
    Console.WriteLine(
        "Rand() was called {0} times. Same number was observed in {1} % cases",
        numElements, probabilityGetSameNumber);
}

Results:

Num of Rand() calls	Same number observed in % of cases	Cases count
10	0	0
100	0	0
1000	0	0
10000	0	0
100000	0.00002999999999997	3
1000000	0.00024100000000004	241
10000000	0.00234760000000001	23476

Technorati Теги: C#,Rand(),probability,LINQ

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Friday, February 19, 2010

Wednesday, February 17, 2010

Impossible to log SQL 2008 performance counters under Windows 2008 64 bit?

Here is some strange problem I’ve experienced (right now it seems to me as a bug in Windows 2008 64 bit):

I have an environment with Windows 2008 64 bit and SQL Enterprise 64 bit.

To begin with - it's possible to see SQL-related performance counters values only in perfmon opened from SysWow64 (i.e. 32 bit) - they are not present in 64-bit perfmon.

Now, if I open perfmon (32 bit) and add any SQL counters (e.g. SQL Latches) to the "Performance Monitor" section I can see that those values are updated "live" in perfmon graphs.

Yet, if I create a new Data Collector Set for the same values under Data Collector Sets -> User Defined - the values for SQL counters are not being stored in the created log file. If I add some other counters (e.g. Processor) they ARE saved.

Seems that this is some sort of bug/problem related to 64 bit…

There are some clues on this problem in two following articles:

but both do not help (for the first one – there is no such service anymore in Windows 2008…