pHDF, H5Fflush and compression


Hello HDF group,

I have a question of the behaviour of H5Fflush() function.

We have build a library on top of the pHDF5 1.12.2 library. In this library we explicitly call the H5Fflush() function before we write the actual data to the file. If this is smart or not is another question. Anyway, if I run my code which makes use of previously mentioned library with 8 ranks it takes about 71 seconds. The data has been written uncompressed to the file. Next, repeated the same thing but now with AEC/SZIP compression. It takes about 46 seconds. Both runs use the H5Fflush() function. I also ran a case without compression and without using the H5Fflush() function and this is about 44 seconds.

Seeing these results, I have the impression that the H5Fflush() works slightly differently in the case with and without compression. Is this true? From this results, it is clear that I should not use the H5Fflush() function to get the best performance.

Best regards,