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Re: [Bacula-devel] Alternative DB proposal


On Tuesday 14 October 2008 10:42:22 Yuri Timofeev wrote:
> 2008/10/14 Kern Sibbald <kern@xxxxxxxxxxx>:
> > On Tuesday 14 October 2008 10:06:22 Yuri Timofeev wrote:
> >> 2008/10/14 Kern Sibbald <kern@xxxxxxxxxxx>:
> >> > On Tuesday 14 October 2008 09:39:27 John Huttley wrote:
> >> >> So the modified version is actually a bit faster?
> >> >
> >> > That is what I understood too, but I wanted to get a confirmation.
> >> >
> >> > If it is indeed the case that the new case runs faster, it is indeed
> >> > odd, and I would say the tester has fallen into a very trap that is
> >> > very common in performance analysis.
> >>
> >> Of course, this is only the first test!
> >> I think that will soon be able to hold a series of tests.
> >> I just limiting the number of entries from 10M to 5M (very long wait)
> >
> > Yes, clearly running something 10 times is not very practical if it takes
> > 35 hours each time, so the test size must be reduced, and you can reduce
> > the number of runs from 10 to say 5.
> >
> > However, what was not at all evident from your first post is that there
> > are apparently subtle differences in schemas that I did not see and
> > differences in the size of the data you were inserting -- and those could
> > possibly explain a large (or even all)  the difference in timings.
>
> In an alternative scheme appear new fields : size, ctime, mtime.
> I therefore reduced length the value that is inserted into the field LStat.
>
> For the old scheme, I used :
> char *lstat = "MI s9MB IG0 B H2 H0 A 9t BAA I BIVsDs BIR93m BIVqaC A A E";
>
> and for the new scheme:
> char *lstat = "MI s9MB IG0 B H2 H0 A 9t BAA I";
>
> But it is not entirely correct.
>
>
>
> In an alternative scheme2 appear new fields : size, ctime, mtime, _atime_.
>
> The new version of the tests, I did as correctly:
> char *lstat = "MI s9MB IG0 B H2 H0 A 9t BAA I BIVsDs BIR93m BIVqaC A A
> E"; /* for traditional scheme */
> char *lstat    = "MI s9MB IG0 B H2 H0 A BAA I BIVsDs BIR93m BIVqaC";
> /* for new scheme */
>
> Therefore, in alternative scheme the length of lstat reduced.
> That is right?

I would not say it is a question of being right or not.  It is a possibility, 
but it would be a big effort to eliminate those fields -- first there is the 
programming problem of finding every place they are accessed and ensuring the 
new fields are used, but even more important, there is the problem of 
converting existing databases from the old scheme to the new one.



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