HDF5 string dataset compression

nathanjsmith · December 11, 2012, 5:20pm

Hi all,

I'm very new to HDF5 and am trying to find an example of how to compress a
string written to an HDF5 file. I've been using the C++ API and writing
scalar strings to my dataset, but I can't figure out how to use data
chunking so that I can enable compression. I tried to adapt the example
provided for Java
(http://www.hdfgroup.org/hdf-java-html/javadocs/ncsa/hdf/object/h5/H5ScalarDS.html#create(java.lang.String,
ncsa.hdf.object.Group, ncsa.hdf.object.Datatype, long[], long[], long[],
int, java.lang.Object):

std::string my_string = function_that_populates_string();
std::string dataset_name = function_that_names_dataset();

StrType datatype(0, H5T_VARIABLE);
DataSpace dataspace(H5S_SCALAR);

    DSetCreatPropList plist;
    hsize_t chunk_dims[1] = {1024};
    plist.setChunk(1, chunk_dims);

DataSet dataset = my_group.createDataSet(dataset_name, datatype,
dataspace, plist);
dataset.write(my_string, datatype);

but it throws errors at runtime:

HDF5-DIAG: Error detected in HDF5 (1.8.6) thread 0:
  #000: H5D.c line 170 in H5Dcreate2(): unable to create dataset
    major: Dataset
    minor: Unable to initialize object
  #001: H5Dint.c line 431 in H5D_create_named(): unable to create and link
to dataset
    major: Dataset
    minor: Unable to initialize object
  #002: H5L.c line 1640 in H5L_link_object(): unable to create new link to
object
    major: Links
    minor: Unable to initialize object
  #003: H5L.c line 1866 in H5L_create_real(): can't insert link
    major: Symbol table
    minor: Unable to insert object
  #004: H5Gtraverse.c line 929 in H5G_traverse(): internal path traversal
failed
    major: Symbol table
    minor: Object not found
  #005: H5Gtraverse.c line 718 in H5G_traverse_real(): traversal operator
failed
    major: Symbol table
    minor: Callback failed
  #006: H5L.c line 1686 in H5L_link_cb(): unable to create object
    major: Object header
    minor: Unable to initialize object
  #007: H5O.c line 3005 in H5O_obj_create(): unable to open object
    major: Object header
    minor: Can't open object
  #008: H5Doh.c line 295 in H5O_dset_create(): unable to create dataset
    major: Dataset
    minor: Unable to initialize object
  #009: H5Dint.c line 1035 in H5D_create(): unable to construct layout
information
    major: Dataset

If I get rid of the provided plist (and hence the chunking), then the code
works without problem. Can anyone point me in the right direction?

Thanks!

Nathan

derobins · December 11, 2012, 6:29pm

Hi Nathan,

···

On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith <nathanjsmith@gmail.com>wrote:

Hi all,

I'm very new to HDF5 and am trying to find an example of how to compress a
string written to an HDF5 file. I've been using the C++ API and writing
scalar strings to my dataset, but I can't figure out how to use data
chunking so that I can enable compression.

Variable-length data cannot be compressed due to the way we store it in the
HDF5 library.

Dana

nathanjsmith · December 11, 2012, 6:32pm

I know the length of the string a priori. Can you point me to an example
of writing out a fixed length string that uses compression?

Thanks!

Nathan

···

On Tue, Dec 11, 2012 at 12:29 PM, Dana Robinson <derobins@hdfgroup.org>wrote:

Hi Nathan,

On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith <nathanjsmith@gmail.com>wrote:

Hi all,

I'm very new to HDF5 and am trying to find an example of how to compress
a string written to an HDF5 file. I've been using the C++ API and writing
scalar strings to my dataset, but I can't figure out how to use data
chunking so that I can enable compression.

Variable-length data cannot be compressed due to the way we store it in
the HDF5 library.

Dana

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

bmribler · December 11, 2012, 6:50pm

Hi Nathan,

Does the example c++/examples/h5group.cpp in our distribution help?

Binh-Minh

···

_____

From: Hdf-forum [mailto:hdf-forum-bounces@hdfgroup.org] On Behalf Of Nathan
Smith
Sent: Tuesday, December 11, 2012 1:33 PM
To: HDF Users Discussion List
Subject: Re: [Hdf-forum] HDF5 string dataset compression

I know the length of the string a priori. Can you point me to an example of
writing out a fixed length string that uses compression?

Thanks!

Nathan

On Tue, Dec 11, 2012 at 12:29 PM, Dana Robinson <derobins@hdfgroup.org> wrote:

Hi Nathan,

On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith <nathanjsmith@gmail.com> wrote:

Hi all,

I'm very new to HDF5 and am trying to find an example of how to compress a
string written to an HDF5 file. I've been using the C++ API and writing
scalar strings to my dataset, but I can't figure out how to use data
chunking so that I can enable compression.

Variable-length data cannot be compressed due to the way we store it in the
HDF5 library.

Dana

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

Peter_Cao · December 11, 2012, 10:26pm

for fixed langth, just replace the H5T_VARIABLE with the length you want to set.

···

On 12/11/2012 12:32 PM, Nathan Smith wrote:

I know the length of the string a priori. Can you point me to an example of writing out a fixed length string that uses compression?

Thanks!

Nathan

On Tue, Dec 11, 2012 at 12:29 PM, Dana Robinson <derobins@hdfgroup.org > <mailto:derobins@hdfgroup.org>> wrote:

    Hi Nathan,

    On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith > <nathanjsmith@gmail.com <mailto:nathanjsmith@gmail.com>> wrote:

        Hi all,

        I'm very new to HDF5 and am trying to find an example of how
        to compress a string written to an HDF5 file. I've been using
        the C++ API and writing scalar strings to my dataset, but I
        can't figure out how to use data chunking so that I can enable
        compression.

    Variable-length data cannot be compressed due to the way we store
    it in the HDF5 library.

    Dana

    _______________________________________________
    Hdf-forum is for HDF software users discussion.
    Hdf-forum@hdfgroup.org <mailto:Hdf-forum@hdfgroup.org>
    http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

nathanjsmith · December 11, 2012, 11:06pm

Hi all,

Thanks for your suggestions. I'm still missing something, though. Using
the h5group.cpp example, I can get my code to create a chunked dataset, but
I can't write anything to it.

std::string dataset_name = function_that_returns_name();
std::string dataset_value = function_that_returns_value();

            // Is the size the size of the buffer, or the length of the
string? (should I include the null-terminator?)
            hsize_t dataset_length = dataset_value.length() + 1;
            StrType datatype(0, dataset_length);
            hsize_t sdims[1];
            sdims[0] = dataset_length;
            DataSpace dataspace(1, sdims);

            DSetCreatPropList plist;
            hsize_t chunk_dims[1];
            chunk_dims[0] = 24;
            plist.setChunk(1, chunk_dims);

DataSet sim_details = group.createDataSet(dataset_name,
datatype, dataspace, plist);

// This raises a bad pointer exception.
sim_details.write(dataset_value, datatype);

  #009: H5FDsec2.c line 846 in H5FD_sec2_write(): file write failed: time =
Tue Dec 11 16:59:46 2012
, filename = 'test.h5', file descriptor = 3, errno = 14, error message =
'Bad address', buf = 0x7f9be0b5a1f8, size = 4115328, offset = 184320
    major: Low-level I/O
    minor: Write failed
terminate called after throwing an instance of 'H5::DataSetIException'

Nathan

···

On Tue, Dec 11, 2012 at 4:26 PM, Peter Cao <xcao@hdfgroup.org> wrote:

for fixed langth, just replace the H5T_VARIABLE with the length you want
to set.

On 12/11/2012 12:32 PM, Nathan Smith wrote:

I know the length of the string a priori. Can you point me to an example
of writing out a fixed length string that uses compression?

Thanks!

Nathan

On Tue, Dec 11, 2012 at 12:29 PM, Dana Robinson <derobins@hdfgroup.org>wrote:

Hi Nathan,

On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith <nathanjsmith@gmail.com>wrote:

Hi all,

I'm very new to HDF5 and am trying to find an example of how to
compress a string written to an HDF5 file. I've been using the C++ API and
writing scalar strings to my dataset, but I can't figure out how to use
data chunking so that I can enable compression.

Variable-length data cannot be compressed due to the way we store it in
the HDF5 library.

Dana

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

_______________________________________________
Hdf-forum is for HDF software users discussion.Hdf-forum@hdfgroup.orghttp://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

bmribler · December 12, 2012, 3:11am

Hi Nathan,

I copied your code below to try and didn't get error. The dataset was
created and written. One difference is, because I didn't have your
function_that_returns_name[value]()s, I defined mine as below:

std::string dataset_name("my dataset");

std::string dataset_value("this dataset has one string");

Binh-Minh

···

_____

From: Hdf-forum [mailto:hdf-forum-bounces@hdfgroup.org] On Behalf Of Nathan
Smith
Sent: Tuesday, December 11, 2012 6:07 PM
To: HDF Users Discussion List
Subject: Re: [Hdf-forum] HDF5 string dataset compression

Hi all,

Thanks for your suggestions. I'm still missing something, though. Using
the h5group.cpp example, I can get my code to create a chunked dataset, but
I can't write anything to it.

std::string dataset_name = function_that_returns_name();

std::string dataset_value = function_that_returns_value();

// Is the size the size of the buffer, or the length of the
string? (should I include the null-terminator?)

hsize_t dataset_length = dataset_value.length() + 1;

StrType datatype(0, dataset_length);

hsize_t sdims[1];

sdims[0] = dataset_length;

DataSpace dataspace(1, sdims);

DSetCreatPropList plist;

hsize_t chunk_dims[1];

chunk_dims[0] = 24;

plist.setChunk(1, chunk_dims);

DataSet sim_details = group.createDataSet(dataset_name,
datatype, dataspace, plist);

// This raises a bad pointer exception.

sim_details.write(dataset_value, datatype);

#009: H5FDsec2.c line 846 in H5FD_sec2_write(): file write failed: time =
Tue Dec 11 16:59:46 2012

, filename = 'test.h5', file descriptor = 3, errno = 14, error message =
'Bad address', buf = 0x7f9be0b5a1f8, size = 4115328, offset = 184320

major: Low-level I/O

minor: Write failed

terminate called after throwing an instance of 'H5::DataSetIException'

Nathan

On Tue, Dec 11, 2012 at 4:26 PM, Peter Cao <xcao@hdfgroup.org> wrote:

for fixed langth, just replace the H5T_VARIABLE with the length you want to
set.

On 12/11/2012 12:32 PM, Nathan Smith wrote:

I know the length of the string a priori. Can you point me to an example of
writing out a fixed length string that uses compression?

Thanks!

Nathan

On Tue, Dec 11, 2012 at 12:29 PM, Dana Robinson <derobins@hdfgroup.org> wrote:

Hi Nathan,

On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith <nathanjsmith@gmail.com> wrote:

Hi all,

I'm very new to HDF5 and am trying to find an example of how to compress a
string written to an HDF5 file. I've been using the C++ API and writing
scalar strings to my dataset, but I can't figure out how to use data
chunking so that I can enable compression.

Variable-length data cannot be compressed due to the way we store it in the
HDF5 library.

Dana

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org

nathanjsmith · December 12, 2012, 5:08pm

Thanks for the update. Using Binh-Minh's strings let me figure out the
problem. My dataset and chunk sizes were wrong. I was specifying that I
had dataset_value.length()+1 *strings* in the output. In fact, I have just
one. That Binh-Minh's example worked is somewhat of luck. HDF5 was
reading past the bounds of the array, which is why I was getting a bad
address exception. Changing the dataset and chunk sizes accordingly made
everything start working. Thanks everyone for your help!

For posterity, the following is the correct way to compress strings:

std::string dataset_name = function_that_returns_name();
std::string dataset_value = function_that_returns_value();

hsize_t dataspace_dims[1] = {1}; // This is the number of strings being
written
hsize_t chunk_dims[1] = {1};

StrType datatype(0, dataset_value.length()+1);
DataSpace dataspace(1, dataspace_dims);

DSetCreatPropList plist;
plist.setChunk(1, chunk_dims);
plist.setDeflate(6);

DataSet sim_details = group.createDataSet(dataset_name, datatype,
dataspace, plist);
sim_details.write(dataset_value, datatype);

Nathan

···

On Tue, Dec 11, 2012 at 9:11 PM, Binh-Minh Ribler <bmribler@hdfgroup.org>wrote:

Hi Nathan,****

** **

I copied your code below to try and didn’t get error. The dataset was
created and written. One difference is, because I didn’t have your
function_that_returns_name[value]()s, I defined mine as below:****

** **

        std::string dataset_name("my dataset");****

        std::string dataset_value("this dataset has one string");****

** **

Binh-Minh****

** **
------------------------------

*From:* Hdf-forum [mailto:hdf-forum-bounces@hdfgroup.org] *On Behalf Of *Nathan
Smith
*Sent:* Tuesday, December 11, 2012 6:07 PM

*To:* HDF Users Discussion List
*Subject:* Re: [Hdf-forum] HDF5 string dataset compression
****

** **

Hi all,****

** **

Thanks for your suggestions. I'm still missing something, though. Using
the h5group.cpp example, I can get my code to create a chunked dataset, but
I can't write anything to it.****

** **

            std::string dataset_name = function_that_returns_name(); ****

            std::string dataset_value = function_that_returns_value();****

        ****

            // Is the size the size of the buffer, or the length of the
string? (should I include the null-terminator?)****

            hsize_t dataset_length = dataset_value.length() + 1;****

            StrType datatype(0, dataset_length);****

            hsize_t sdims[1];****

            sdims[0] = dataset_length;****

            DataSpace dataspace(1, sdims);****

** **

            DSetCreatPropList plist;****

            hsize_t chunk_dims[1];****

            chunk_dims[0] = 24;****

            plist.setChunk(1, chunk_dims);****

** **

            DataSet sim_details = group.createDataSet(dataset_name,
datatype, dataspace, plist);****

** **

            // This raises a bad pointer exception.****

            sim_details.write(dataset_value, datatype);****

** **

** **

  #009: H5FDsec2.c line 846 in H5FD_sec2_write(): file write failed: time
= Tue Dec 11 16:59:46 2012****

, filename = 'test.h5', file descriptor = 3, errno = 14, error message =
'Bad address', buf = 0x7f9be0b5a1f8, size = 4115328, offset = 184320****

    major: Low-level I/O****

    minor: Write failed****

terminate called after throwing an instance of 'H5::DataSetIException'****

** **

Nathan****

** **

** **

On Tue, Dec 11, 2012 at 4:26 PM, Peter Cao <xcao@hdfgroup.org> wrote:****

for fixed langth, just replace the H5T_VARIABLE with the length you want
to set.****

** **

On 12/11/2012 12:32 PM, Nathan Smith wrote:****

I know the length of the string a priori. Can you point me to an example
of writing out a fixed length string that uses compression? ****

** **

Thanks!****

** **

Nathan****

On Tue, Dec 11, 2012 at 12:29 PM, Dana Robinson <derobins@hdfgroup.org>
wrote:****

Hi Nathan,****

On Tue, Dec 11, 2012 at 11:20 AM, Nathan Smith <nathanjsmith@gmail.com>
wrote:****

Hi all, ****

** **

I'm very new to HDF5 and am trying to find an example of how to compress a
string written to an HDF5 file. I've been using the C++ API and writing
scalar strings to my dataset, but I can't figure out how to use data
chunking so that I can enable compression. ****

** **

Variable-length data cannot be compressed due to the way we store it in
the HDF5 library.****

** **

Dana ****

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org****

** **

****

_______________________________________________****

Hdf-forum is for HDF software users discussion.****

Hdf-forum@hdfgroup.org****

http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org****

** **

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org****

** **

_______________________________________________
Hdf-forum is for HDF software users discussion.
Hdf-forum@hdfgroup.org
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org