H5Part development and discussion

["Schietinger Thomas" <thomas.schietinger AT psi.ch>]

Hello Kurt,

let me answer your comments/questions:

>> get file attribute info:
>>
>>   for (Int_t n = 0; n < fNFileAttr; n++) {
>>     H5PartGetFileAttribInfo(fH5File,n,an,32,0,nElem);
>Is it intended that you don't return the type of the attribute (the 5th
>parameter) or do you assume that you know the type, i.e. all are of type
>char?

I, uh, copied the command from somewhere else, and it has worked ever since.
Now that I look at it, you are right, I should probably check for the
type to make sure it is indeed a char...

>> where GetUnit(...) is a method that contains a loop over the file
>> attributes to
>> find the associated unit name:
>In the H5Part doc I didn't find anything specific about unit names. Can
>you explain this a bit? Do you assume that the attribute name is unified
>to char[32]?

This is a "private" H5Part convention between Andreas and me: whenever an
attribute string is followed by "Unit" it is understood to contain a string
describing the unit of the attribute. Example: "x" -> "xUnit". In the studies
we are doing now, it is very important to know in what unit a given quantity
is stored, in particular if you want to compare different files. If this 
turns out to be a universally desirable feature, one could think about
implementing it "officially" in H5Part.
In H5root, I just use it to display the unit in square brackets on the plots,
there is no automatic unit conversion yet.

>> Now some numbers: a 3 Giga file with some 500 time steps (21 file
>> attr., 12 step
>> attr.) takes 19.1 s to read in (the second time only 0.5 s since the
>> file is
>> buffered). 
>This the time for reading the attributes only, right? If yes, then the
>whole 3GB is not read entirely but only the 21*12 (char) attributes, right?

See Achim's reply.

>Can you send me a pointer to the file to download so that we can look at
>this together? This would also help me understand your performance a bit
>better.

The file is on merlin, /home2/adelmann/lcls-small.h5 . Does anyone have 
access to merlin overthere?

Cheers,

Thomas