hdf5/examples/h5_shared_mesg.c

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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Copyright by The HDF Group. *
* Copyright by the Board of Trustees of the University of Illinois. *
* All rights reserved. *
* *
* This file is part of HDF5. The full HDF5 copyright notice, including *
* terms governing use, modification, and redistribution, is contained in *
* the files COPYING and Copyright.html. COPYING can be found at the root *
* of the source code distribution tree; Copyright.html can be found at the *
* root level of an installed copy of the electronic HDF5 document set and *
* is linked from the top-level documents page. It can also be found at *
* http://hdfgroup.org/HDF5/doc/Copyright.html. If you do not have *
* access to either file, you may request a copy from help@hdfgroup.org. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*
* This program illustrates the usage of HDF5's implicit message sharing
* feature, which can be used to save space when the same messages are
* used many times in a file.
*
* This example creates a standard file using file creation property lists
* to control which messages are shared. Messages that can be shared are
* datatypes, dataspaces, attributes, fill values, and filter pipelines.
*
*/
#include <stdlib.h>
#include "hdf5.h"
#define NUM_DATASETS 40
const char* DSETNAME[] = {
"dataset0", "dataset1",
"dataset2", "dataset3",
"dataset4", "dataset5",
"dataset6", "dataset7",
"dataset8", "dataset9",
"dataset10", "dataset11",
"dataset12", "dataset13",
"dataset14", "dataset15",
"dataset16", "dataset17",
"dataset18", "dataset19",
"dataset20", "dataset21",
"dataset22", "dataset23",
"dataset24", "dataset25",
"dataset26", "dataset27",
"dataset28", "dataset29",
"dataset30", "dataset31",
"dataset32", "dataset33",
"dataset34", "dataset35",
"dataset36", "dataset37",
"dataset38", "dataset39",
NULL
};
herr_t create_standard_file(const char *filename, hid_t fcpl);
/*-------------------------------------------------------------------------
* Function: main
*
* Purpose: Enables shared messages using File Creation Property Lists
* and creates files using these settings.
*
*-------------------------------------------------------------------------
*/
int main(void)
{
hid_t fcpl_id;
herr_t ret;
/* Create a file creation property list */
fcpl_id = H5Pcreate(H5P_FILE_CREATE);
if(fcpl_id < 0) goto error;
/* The file creation property list is the default list right now.
* Create a file using it (this is the same as creating a file with
* H5P_DEFAULT). Implicit shared messages will be disabled.
*/
ret = create_standard_file("default_file.h5", fcpl_id);
if(ret < 0) goto error;
/* There are five kinds of messages that can be shared: datatypes,
* dataspaces, attributes, fill values, and filter pipelines.
* Shared messages are stored in up to five "indexes," where each
* index can contain one or more types of message. Using more indexes
* will result in more overhead for sharing, but can also provide
* more "tunability" and may affect caching performance.
*/
/* To begin with, use only one index. */
ret = H5Pset_shared_mesg_nindexes(fcpl_id, 1);
if(ret < 0) goto error;
/* Each index has a "minimum message size" for a message of that
* type to be shared. Since sharing a message creates some overhead,
* this is to prevent this overhead for very small messages when little
* space would be saved by sharing them anyway.
* If the content of the file isn't known beforehand, it's probably best
* to set the minimum size "high"; over 100 or 200 bytes. If the content
* of the file is known, this value can be used to trade space saved for
* performance lost. The smaller this value is, the more messages will
* be shared, so the more overhead will be incurred.
* This value is in bytes. A shared message involves about 30 bytes of
* overhead. Note that even messages that are only written once will
* require this overhead (since they "might" be shared in the future),
* so setting the minimum size too low may result in a file actually growing
* in size.
* For this example case, we'll set the minimum sharing size to be small
* since we know that every message the "standard" file uses will be
* repeated many times.
*/
/* The other property that each index has is the kinds of messages that
* it holds. For the simple case, we'll put every message that could be
* shared in this single index.
*/
ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_SHMESG_ALL_FLAG, 40);
if(ret < 0) goto error;
/* The other property that can be set for shared messages is the
* list/B-tree cutoff for the indexes.
* Each shared message index beins life as a simple list of messages
* and becomes a B-tree when "too many" messages are written to it.
* This keeps the indexes simple when only a few messages are shared,
* but allows them to scale for many messages. If many messages are
* deleted from the B-tree, it scales back down into a list.
* A "resonable" setting for maximum list size and minimum btree size
* depends on what kinds of messages will be stored in the file.
* These numbers are the same for all indexes in a file.
* We'll guess at some numbers, though we could just as easily have kept
* the default values. The first value is the maximum list size, the
* second the minimum B-tree size.
*/
ret = H5Pset_shared_mesg_phase_change(fcpl_id, 30, 20);
if(ret < 0) goto error;
/* Now create a file with this property list. After the FCPL is used,
* everything is automatic; messages will be shared and this will be
* completely transparent to the user. Even if the file is closed
* and re-opened, this settings will be saved and applied to messages
* written later.
*/
ret = create_standard_file("one_index_file.h5", fcpl_id);
if(ret < 0) goto error;
/* Now try some variations on this. The FCPL hasn't been closed, so
* we don't need to re-create it.
* For instance, if we set the index to only share very large
* messages, none of the messages we write will qualify and the file
* will be about the same size as a normal file (with just a little extra
* overhead).
*/
ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_SHMESG_ALL_FLAG, 1000);
if(ret < 0) goto error;
ret = create_standard_file("only_huge_mesgs_file.h5", fcpl_id);
if(ret < 0) goto error;
/* Or, suppose we only wanted to shared dataspaces and
* attributes (which might make sense if we were going to use committed
* datatypes). We could change the flags on the index:
*/
ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_SHMESG_SDSPACE_FLAG | H5O_SHMESG_ATTR_FLAG, 40);
if(ret < 0) goto error;
ret = create_standard_file("only_dspaces_and_attrs_file.h5", fcpl_id);
if(ret < 0) goto error;
/* We could create a second index and put attributes in it to separate them
* from datatypes and dataspaces (and then run some performance metrics to
* see whether this improved caching performance).
*/
ret = H5Pset_shared_mesg_nindexes(fcpl_id, 2);
if(ret < 0) goto error;
ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_SHMESG_DTYPE_FLAG | H5O_SHMESG_SDSPACE_FLAG, 40);
if(ret < 0) goto error;
ret = H5Pset_shared_mesg_index(fcpl_id, 1, H5O_SHMESG_ATTR_FLAG, 40);
if(ret < 0) goto error;
ret = create_standard_file("separate_indexes_file.h5", fcpl_id);
if(ret < 0) goto error;
/* We can try twiddling the "phase change" values and see what it does to
* the file size. Since there's only a few different messages (two
* datatypes, two dataspaces, and one attribute), using smaller lists will
* save some space.
*/
ret = H5Pset_shared_mesg_nindexes(fcpl_id, 1);
if(ret < 0) goto error;
ret = H5Pset_shared_mesg_index(fcpl_id, 0, H5O_SHMESG_ALL_FLAG, 40);
if(ret < 0) goto error;
ret = H5Pset_shared_mesg_phase_change(fcpl_id, 5, 0);
if(ret < 0) goto error;
ret = create_standard_file("small_lists_file.h5", fcpl_id);
if(ret < 0) goto error;
/* Or we could create indexes that are never lists, but are created as
* B-trees. We do this by setting the "maximum list size" to zero.
*/
ret = H5Pset_shared_mesg_phase_change(fcpl_id, 0, 0);
if(ret < 0) goto error;
ret = create_standard_file("btrees_file.h5", fcpl_id);
if(ret < 0) goto error;
/* Obviously there are a lot more permutations of these options possible.
* Performance will often be a tradeoff of speed for space, but will
* depend a great deal on the specific application. If performance is
* important, the best thing to do is to play with these settings to find
* the ones that work best for you.
* Please let The HDF Group (help@hdfgroup.org) know what you find!
*/
/* Close the property list */
ret = H5Pclose(fcpl_id);
if(ret < 0) goto error;
return 0;
error:
return -1;
}
/*-------------------------------------------------------------------------
* Function: create_standard_file
*
* Purpose: A helper functon for the example. Creates an HDF5 file
* with many repeated messages using the file creation
* property list FCPL.
*
* This function only uses datatypes, dataspaces, and
* attributes. Fill values and filter pipelines can also
* be shared in the same way (i.e., by enabling sharing in
* the FCPL and writing the same message more than once).
*-------------------------------------------------------------------------
*/
herr_t
create_standard_file(const char *filename, hid_t fcpl_id)
{
hid_t file_id=-1;
hid_t type_id=-1, temp_type_id=-1;
hsize_t dims[] = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
hid_t space_id=-1;
hid_t attr_type_id = -1;
hid_t attr_space_id = -1;
int attr_data[] = {1,2,3,4,5,6,7,8,9,0};
hid_t dset_id=-1;
hid_t attr_id=-1;
int x;
herr_t ret;
/* Create the file */
file_id = H5Fcreate(filename, H5F_ACC_TRUNC, fcpl_id, H5P_DEFAULT);
if(file_id < 0) goto error;
/* Create the datatype we'll be using. Generally, sharing messages
* is most useful when the message is complex and takes more space on
* disk, so this type will be an array type rather than an atomic type.
* However, any type can be shared.
*/
temp_type_id = H5Tarray_create2(H5T_NATIVE_INT, 2, dims);
if(temp_type_id < 0) goto error;
type_id = H5Tarray_create2(temp_type_id, 2, dims);
if(type_id < 0) goto error;
ret = H5Tclose(temp_type_id);
if(ret < 0) goto error;
/* Create the dataspace we'll be using.
* Again, create a more complex dataspace so that more space will
* be saved when we share it.
*/
space_id = H5Screate_simple(10, dims, dims);
if(space_id < 0) goto error;
/* Create a datatype and dataspace for the attributes we'll be creating.
* The datatype will be a single integer, and each attribute will hold
* 10 integers.
*/
attr_type_id = H5Tcopy(H5T_NATIVE_INT);
if(attr_type_id < 0) goto error;
attr_space_id = H5Screate_simple(1, dims, dims);
if(attr_space_id < 0) goto error;
/* Begin using the messages many times. Do this by creating datasets
* that use this datatype, dataspace, and have this attribute.
*/
for(x = 0; x < NUM_DATASETS; ++x) {
/* Create a dataset */
dset_id = H5Dcreate2(file_id, DSETNAME[x], type_id, space_id, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
if(dset_id < 0) goto error;
/* Create an attribute on the dataset */
attr_id = H5Acreate2(dset_id, "attr_name", attr_type_id, attr_space_id, H5P_DEFAULT, H5P_DEFAULT);
if(attr_id < 0) goto error;
/* Write data to the attribute */
ret = H5Awrite(attr_id, H5T_NATIVE_INT, attr_data);
if(ret < 0) goto error;
ret = H5Aclose(attr_id);
if(ret < 0) goto error;
ret = H5Dclose(dset_id);
if(ret < 0) goto error;
}
/* Close all open IDs */
ret = H5Tclose(attr_type_id);
if(ret < 0) goto error;
ret = H5Sclose(attr_space_id);
if(ret < 0) goto error;
ret = H5Tclose(type_id);
if(ret < 0) goto error;
ret = H5Sclose(space_id);
if(ret < 0) goto error;
ret = H5Fclose(file_id);
if(ret < 0) goto error;
return 0;
error:
return -1;
}