Describes HDF5 Release 1.8.20, November 2017.
HDF5 functions described is this section are implemented in the HDF5 High-level Library as optimized functions. These functions generally require careful setup and testing as they enable an application to bypass portions of the HDF5 Library’s I/O pipeline for performance purposes.
These functions are distributed in the standard HDF5 distribution and are available any time the HDF5 High-level Library is available.
The C Interfaces:
|
Dataset I/O Optimization |
H5DOwrite_chunk(
hid_t dset_id,
hid_t dxpl_id,
uint32_t filter_mask,
hsize_t *offset,
size_t data_size,
const void *buf
)
H5DOwrite_chunk writes a raw data chunk
as specified by its logical offset
in a chunked dataset dset_id from
the application memory buffer buf to the dataset in the file.
Typically, the data in buf is preprocessed in memory
by a custom transformation, such as compression.
The chunk will bypass the library’s internal data
transfer pipeline, including filters, and
will be written directly to the file.
dxpl_id is a data transfer property list identifier.
filter_mask is a mask providing a record of which
filters are used with the chunk.
The default value of the mask is zero (0),
indicating that all enabled filters are applied.
A filter is skipped if the bit corresponding to the filter’s
position in the pipeline
(0 ≤ position < 32) is turned on.
This mask is saved with the chunk in the file.
offset is an array specifying the logical position
of the first element of the chunk in the dataset’s
dataspace. The length of the offset array must equal the number
of dimensions, or rank, of the dataspace.
The values in offset must not exceed the dimension
limits and must specify a point that falls on a dataset chunk boundary.
data_size is the size in bytes of the chunk,
representing the number of bytes to be read from the buffer
buf. If the chunk has been precompressed,
data_size should be the size of the compressed data.
buf is the memory buffer containing data to be written to the chunk in the file.
hid_t dset_id |
IN: Identifier for the dataset to write to |
hid_t dxpl_id |
IN: Transfer property list identifier for
this I/O operation
|
uint32_t filter_mask |
IN: Mask for identifying the filters in use |
hsize_t *offset |
IN: Logical position of the chunk’s first element in the dataspace |
size_t data_size |
IN: Size of the actual data to be written in bytes |
const void *buf |
IN: Buffer containing data to be written to the chunk |
H5DOwrite_chunk
to write an entire dataset, chunk by chunk:
#include <zlib.h>
#include <math.h>
#define DEFLATE_SIZE_ADJUST(s) (ceil(((double)(s))*1.001)+12)
:
:
size_t buf_size = CHUNK_NX*CHUNK_NY*sizeof(int);
const Bytef *z_src = (const Bytef*)(direct_buf);
Bytef *z_dst; /* Destination buffer */
uLongf z_dst_nbytes = (uLongf)DEFLATE_SIZE_ADJUST(buf_size);
uLong z_src_nbytes = (uLong)buf_size;
int aggression = 9; /* Compression aggression setting */
uint32_t filter_mask = 0;
size_t buf_size = CHUNK_NX*CHUNK_NY*sizeof(int);
/* Create the data space */
if((dataspace = H5Screate_simple(RANK, dims, maxdims)) < 0)
goto error;
/* Create a new file */
if((file = H5Fcreate(FILE_NAME5, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)) < 0)
goto error;
/* Modify dataset creation properties, i.e. enable chunking and compression */
if((cparms = H5Pcreate(H5P_DATASET_CREATE)) < 0)
goto error;
if((status = H5Pset_chunk( cparms, RANK, chunk_dims)) < 0)
goto error;
if((status = H5Pset_deflate( cparms, aggression)) < 0)
goto error;
/* Create a new dataset within the file using cparms creation properties */
if((dset_id = H5Dcreate2(file, DATASETNAME, H5T_NATIVE_INT, dataspace, H5P_DEFAULT,
cparms, H5P_DEFAULT)) < 0)
goto error;
/* Initialize data for one chunk */
for(i = n = 0; i < CHUNK_NX; i++)
for(j = 0; j < CHUNK_NY; j++)
direct_buf[i][j] = n++;
/* Allocate output (compressed) buffer */
outbuf = malloc(z_dst_nbytes);
z_dst = (Bytef *)outbuf;
/* Perform compression from the source to the destination buffer */
ret = compress2(z_dst, &z_dst_nbytes, z_src, z_src_nbytes, aggression);
/* Check for various zlib errors */
if(Z_BUF_ERROR == ret) {
fprintf(stderr, "overflow");
goto error;
} else if(Z_MEM_ERROR == ret) {
fprintf(stderr, "deflate memory error");
goto error;
} else if(Z_OK != ret) {
fprintf(stderr, "other deflate error");
goto error;
}
/* Write the compressed chunk data repeatedly to cover all the
* chunks in the dataset, using the direct write function. */
for(i=0; i<NX/CHUNK_NX; i++) {
for(j=0; j<NY/CHUNK_NY; j++) {
status = H5DOwrite_chunk(dset_id, H5P_DEFAULT, filter_mask,
offset, z_dst_nbytes, outbuf);
offset[1] += CHUNK_NY;
}
offset[0] += CHUNK_NX;
offset[1] = 0;
}
/* Overwrite the first chunk with uncompressed data. Set the filter mask to
* indicate the compression filter is skipped */
filter_mask = 0x00000001;
offset[0] = offset[1] = 0;
if(H5DOwrite_chunk(dset_id, H5P_DEFAULT, filter_mask, offset, buf_size,
direct_buf) < 0)
goto error;
/* Read the entire dataset back for data verification converting ints to longs */
if(H5Dread(dataset, H5T_NATIVE_LONG, H5S_ALL, H5S_ALL, H5P_DEFAULT,
outbuf_long) < 0)
goto error;
/* Data verification here */
:
:
| Release | Change |
| 1.8.11 | C function introduced in this release. |
H5DOread_chunk(
hid_t dset_id,
hid_t dxpl_id,
const hsize_t *offset,
uint32_t *filter_mask,
void *buf
)
H5DOread_chunk reads a raw data chunk
as specified by its logical offset in
a chunked dataset dset_id
from the dataset in the file into the application memory buffer buf.
The data in buf is read directly from the file
bypassing the library’s internal data
transfer pipeline, including filters.
dxpl_id is a data transfer property list identifier.
The mask filter_mask indicates which filters are used
with the chunk when written.
A zero value indicates that all enabled filters are applied on the chunk.
A filter is skipped if the bit corresponding to the filter’s
position in the pipeline
(0 ≤ position < 32) is turned on.
offset is an array specifying the logical position
of the first element of the chunk in the dataset’s
dataspace. The length of the offset array must equal the number
of dimensions, or rank, of the dataspace.
The values in offset must not exceed the dimension
limits and must specify a point that falls on a dataset chunk boundary.
buf is the memory buffer containing the chunk read from the dataset in the file.
hid_t dset_id |
IN: Identifier for the dataset to be read |
hid_t dxpl_id |
IN: Transfer property list identifier for this I/O operation |
uint32_t * filter_mask |
IN: Mask for identifying the filters used with the chunk |
const hsize_t *offset |
IN: Logical position of the chunk’s first element in the dataspace |
void *buf |
IN: Buffer containing the chunk read from the dataset |
H5DOread_chunk
to read a chunk from a dataset:
#include <zlib.h>
#include <math.h>
#define DEFLATE_SIZE_ADJUST(s) (ceil(((double)(s))*1.001)+12)
:
:
size_t buf_size = CHUNK_NX*CHUNK_NY*sizeof(int);
const Bytef *z_src = (const Bytef*)(direct_buf);
Bytef *z_dst; /* Destination buffer */
uLongf z_dst_nbytes = (uLongf)DEFLATE_SIZE_ADJUST(buf_size);
uLong z_src_nbytes = (uLong)buf_size;
int aggression = 9; /* Compression aggression setting */
uint32_t filter_mask = 0;
size_t buf_size = CHUNK_NX*CHUNK_NY*sizeof(int);
/* For H5DOread_chunk() */
void *readbuf = NULL; /* Buffer for reading data */
const Bytef *pt_readbuf; /* Point to the buffer for data read */
hsize_t read_chunk_nbytes; /* Size of chunk on disk */
int read_dst_buf[CHUNK_NX][CHUNK_NY]; /* Buffer to hold un-compressed data */
/* Create the data space */
if((dataspace = H5Screate_simple(RANK, dims, maxdims)) < 0)
goto error;
/* Create a new file */
if((file = H5Fcreate(FILE_NAME5, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)) < 0)
goto error;
/* Modify dataset creation properties, i.e. enable chunking and compression */
if((cparms = H5Pcreate(H5P_DATASET_CREATE)) < 0)
goto error;
if((status = H5Pset_chunk( cparms, RANK, chunk_dims)) < 0)
goto error;
if((status = H5Pset_deflate( cparms, aggression)) < 0)
goto error;
/* Create a new dataset within the file using cparms creation properties */
if((dset_id = H5Dcreate2(file, DATASETNAME, H5T_NATIVE_INT, dataspace, H5P_DEFAULT,
cparms, H5P_DEFAULT)) < 0)
goto error;
/* Initialize data for one chunk */
for(i = n = 0; i < CHUNK_NX; i++)
for(j = 0; j < CHUNK_NY; j++)
direct_buf[i][j] = n++;
/* Allocate output (compressed) buffer */
outbuf = malloc(z_dst_nbytes);
z_dst = (Bytef *)outbuf;
/* Perform compression from the source to the destination buffer */
ret = compress2(z_dst, &z_dst_nbytes, z_src, z_src_nbytes, aggression);
/* Check for various zlib errors */
if(Z_BUF_ERROR == ret) {
fprintf(stderr, "overflow");
goto error;
} else if(Z_MEM_ERROR == ret) {
fprintf(stderr, "deflate memory error");
goto error;
} else if(Z_OK != ret) {
fprintf(stderr, "other deflate error");
goto error;
}
/* Write the compressed chunk data repeatedly to cover all the
* chunks in the dataset, using the direct write function. */
for(i=0; i<NX/CHUNK_NX; i++) {
for(j=0; j<NY/CHUNK_NY; j++) {
status = H5DOwrite_chunk(dset_id, H5P_DEFAULT, filter_mask,
offset, z_dst_nbytes, outbuf);
offset[1] += CHUNK_NY;
}
offset[0] += CHUNK_NX;
offset[1] = 0;
}
if(H5Fflush(dataset, H5F_SCOPE_LOCAL) < 0)
goto error;
if(H5Dclose(dataset) < 0)
goto error;
if((dataset = H5Dopen2(file, DATASETNAME1, H5P_DEFAULT)) < 0)
goto error;
offset[0] = CHUNK_NX;
offset[1] = CHUNK_NY;
/* Get the size of the compressed chunk */
ret = H5Dget_chunk_storage_size(dataset, offset, &read_chunk_nbytes);
readbuf = HDmalloc(read_chunk_nbytes);
pt_readbuf = (const Bytef *)readbuf;
/* Use H5DOread_chunk() to read the chunk back */
if((status = H5DOread_chunk(dataset, H5P_DEFAULT, offset, &read_filter_mask, readbuf)) < 0)
goto error;
ret = uncompress((Bytef *)read_dst_buf, (uLongf *)&buf_size, pt_readbuf, (uLong)read_chunk_nbytes);
/* Check for various zlib errors */
if(Z_BUF_ERROR == ret) {
fprintf(stderr, "error: not enough room in output buffer");
goto error;
} else if(Z_MEM_ERROR == ret) {
fprintf(stderr, "error: not enough memory");
goto error;
} else if(Z_OK != ret) {
fprintf(stderr, "error: corrupted input data");
goto error;
}
/* Data verification here */
:
:
| Release | Change |
| 1.8.19 | C function introduced in this release. |
|
The HDF Group Help Desk:
Describes HDF5 Release 1.8.20, November 2017. | Copyright by The HDF Group |