Unexpected Standard exception from MEX file when reading h5 file

Hi All, I am using matlab 2022a to read h5 file from my mobile disk. The h5disp command returns the following information:

>> h5disp('F:\NREL\western_wind_2006.h5')
HDF5 western_wind_2006.h5 
Group '/' 
    Dataset 'capacity100m' 
        Size:  32043x52560
        MaxSize:  32043x52560
        Datatype:   H5T_IEEE_F64LE (double)
        ChunkSize:  101x52560
        Filters:  none
        Attributes:
            'capacity100m':  'MW'
    Dataset 'meta' 
        Size:  32043
        MaxSize:  32043
        Datatype:   H5T_COMPOUND
            Member 'site_id':  H5T_STD_I32LE (int32)
            Member 'latitude':  16-bit floating point type
            Member 'longitude':  16-bit floating point type
            Member 'power_density':  16-bit floating point type
            Member 'capacity_factor':  16-bit floating point type
            Member 'wind_speed':  16-bit floating point type
            Member 'state_code':  H5T_STRING
                String Length: 8
                Padding: H5T_STR_NULLPAD
                Character Set: H5T_CSET_ASCII
                Character Type: H5T_C_S1
            Member 'elevation':  16-bit floating point type
        ChunkSize:  []
        Filters:  none
        FillValue:  H5T_COMPOUND
        Attributes:
            'wind_speed':  'm/s'
            'elevation':  'm'
            'longitude':  'decimal degree'
            'power_density':  'W/m2'
            'capacity_factor':  '%'
            'latitude':  'decimal degree'
    Dataset 'speed100m' 
        Size:  32043x52560
        MaxSize:  32043x52560
        Datatype:   H5T_IEEE_F64LE (double)
        ChunkSize:  101x52560
        Filters:  none
        Attributes:
            'speed100m':  'm/s'
    Dataset 'time_index' 
        Size:  52560
        MaxSize:  52560
        Datatype:   H5T_STRING
            String Length: 30
            Padding: H5T_STR_NULLPAD
            Character Set: H5T_CSET_ASCII
            Character Type: H5T_C_S1
        ChunkSize:  []
        Filters:  none
        FillValue:  '                              '

When I read the dataset 'meta' or 'time_index', matlab always runs quickly and successfully. However, if I read the 'capacity100m' or 'speed100m', it will cost much more time and it will often present the following error:

>> d=h5read('F:\NREL\western_wind_2006.h5','/capacity100m');
Unexpected Standard exception from MEX file.
What() is:bad allocation
..

Error in h5read (line 93)
[data,var_class] = h5readc(Filename,Dataset,start,count,stride);

I am wondering what causes this problem. Why sometiomes I can read the 'capacity100m' dataset successfully and sometimes not? Any suggestion will be appreciated. Thank you very much.

Answer 1

[Manoj Mirge]

Hi,

The error you are getting is might be due to a memory issue. The h5read function reads datasets and creates a matrix of that dataset in MATLAB and that matrix is stored in your computer memory. If the underlying MEX file couldn’t get free memory for allocation of data, it will throw the error you are getting.

In your case, the 'capacity100m' and 'speed100m' datasets have exceptionally large size compared to ‘meta’ and ‘time_index’ datasets. That is why you can read the ‘meta’ and ‘time_index’ datasets quickly and without any error compared to other datasets.

Sometimes, if you are running other programs with your MATLAB code on your computer, other programs may occupy the memory needed by the MEX file and at that time you will get error by MEX file. That is why you can sometimes read datasets successfully because you may not have other programs running with your code at that same time.

You can check the memory usage of various programs running on your computer in the Task Manager.

To read more about this error, you can check this MATLAB answer thread.

Hope this helps.

[元熙 吴]

Thank you very much.