[Rock-dev] Questions Regarding Typelib

[Sylvain Joyeux]

>
>
>> Created a dataset of one minute with 100 streams. Each stream is at
>> 100Hz, so that's 600k samples. It took 4.6 seconds to generate the index
>> and 0.8 seconds to load the file index (from warm cache, so with probably
>> little I/O overhead).
>>
> How long did the stream alignment take ? This is the part were usually the
> problem is, as you can't get better than
> O((log n)*s) there, were n is the number of streams and s the amount of
> samples.

??? What are you talking about ? This is only the asymptotic curve. The
alignment takes 4.6 seconds.

>
>
>> C++ *is* faster. Of course it is. From what I see, not fast enough to
>> justify the refactoring that you are proposing.
>>
> Ohh yes, it does. Recently I did a log of localization debugging. You
> can't jump data in this case (and a lot of other usecases too) which means
> you have to replay the whole logstream. If the replay is double as fast, it
> means you need half
> the time for debugging. So in my eyes it is 100% worth the effort.

Except that making twice as fast the part that is currently taking 10% of
the replay time only will make the overall process 5% faster. Even making
it 100 times faster will only save 9%. This is from what I see what you are
attempting, as what takes the most time is I/O and typelib demarshalling.

In other words: you are attempting to optimize something without having
done any profiling. This is a cardinal sin.


Again, you are *not* giving the right measurements. Speed factors and
>> durations are meaningless if we don't know how many samples each stream
>> has, and how long each stream lasts. Just "it is 24x times faster" means
>> nothing.
>>
> You got the C++ implementation, just run multiIndexTester on your testdata
> and compare the results.
>

Sylvain
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