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Howdy all!
I am writing a test program which writes large files (well over 2
GB). I have some questions about HDF5 and very large files. I need to
check out whether netCDF-4 has been correctly implemented for best
performance.
In the program below, I create 4 datasets, of type double. They are
one-dimensional, with length 2147483644/4. (That is 17179869152 bytes
of data.)
Then I write the last value only in each dataset.
Took a really long time - minutes. Is this expected? What is HDF5
doing in the background here? Is there something I can do with
chunking here to improve the speed of this program?
I am not setting a fill calue, so what is being written here? I
naively expected that HDF5 would not write all the data I am skipping,
but would find a way to write data only around the value that I am
actually writing...
The file that this program creates is 17179883735 bytes, which is
14583 bytes of HDF5 overhead. Is that about what is expected?
Any comments welcome...
Thanks,
Ed
/*
Copyright 2007, UCAR/Unidata
See COPYRIGHT file for copying and redistribution conditions.
This program (quickly, but not throughly) tests the large file
features of netCDF-4.
$Id: tst_large.c,v 1.3 2007/08/18 12:26:38 ed Exp $
*/
#include <config.h>
#include <nc_tests.h>
#include <netcdf.h>
#include <stdio.h>
#include <string.h>
/* This is the magic number for classic format limits: 2 GiB - 4
bytes. */
#define MAX_CLASSIC_BYTES 2147483644
/* This is the magic number for 64-bit offset format limits: 4 GiB - 4
bytes. */
#define MAX_64OFFSET_BYTES 4294967292
/* Handy for constucting tests. */
#define QTR_CLASSIC_MAX (MAX_CLASSIC_BYTES/4)
/* We will create this file. */
#define FILE_NAME "tst_large.nc"
int
main(int argc, char **argv)
{
printf("\n*** Testing really large files in netCDF-4/HDF5 format,
quickly.\n");
printf("\n*** Testing create of simple, but large, file...");
{
#define DIM_NAME "Time_in_nanoseconds"
#define NUMDIMS 1
#define NUMVARS 4
int ncid, dimids[NUMDIMS], varid[NUMVARS];
char var_name[NUMVARS][NC_MAX_NAME + 1] = {"England", "Scotland",
"Ireland", "Wales"};
size_t index[2] = {QTR_CLASSIC_MAX-1, 0};
int ndims, nvars, natts, unlimdimid;
nc_type xtype;
char name_in[NC_MAX_NAME + 1];
size_t len;
double pi = 3.1459, pi_in;
int i;
/* Create a netCDF netCDF-4/HDF5 format file, with 4 vars. */
if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
if (nc_set_fill(ncid, NC_NOFILL, NULL)) ERR;
if (nc_def_dim(ncid, DIM_NAME, QTR_CLASSIC_MAX, dimids)) ERR;
for (i = 0; i < NUMVARS; i++)
{
if (nc_def_var(ncid, var_name[i], NC_DOUBLE, NUMDIMS,
dimids, &varid[i])) ERR;
}
if (nc_enddef(ncid)) ERR;
for (i = 0; i < NUMVARS; i++)
if (nc_put_var1_double(ncid, i, index, &pi)) ERR;
if (nc_close(ncid)) ERR;
/* Reopen and check the file. */
if (nc_open(FILE_NAME, 0, &ncid)) ERR;
if (nc_inq(ncid, &ndims, &nvars, &natts, &unlimdimid)) ERR;
if (ndims != NUMDIMS || nvars != NUMVARS || natts != 0 || unlimdimid !=
-1) ERR;
if (nc_inq_dimids(ncid, &ndims, dimids, 1)) ERR;
if (ndims != 1 || dimids[0] != 0) ERR;
if (nc_inq_dim(ncid, 0, name_in, &len)) ERR;
if (strcmp(name_in, DIM_NAME) || len != QTR_CLASSIC_MAX) ERR;
for (i = 0; i < NUMVARS; i++)
{
if (nc_inq_var(ncid, i, name_in, &xtype, &ndims, dimids, &natts)) ERR;
if (strcmp(name_in, var_name[i]) || xtype != NC_DOUBLE || ndims != 1
||
dimids[0] != 0 || natts != 0) ERR;
if (nc_get_var1_double(ncid, i, index, &pi_in)) ERR;
if (pi_in != pi) ERR;
}
if (nc_close(ncid)) ERR;
}
SUMMARIZE_ERR;
FINAL_RESULTS;
}
--
Ed Hartnett -- ed@xxxxxxxxxxxxxxxx
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