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HDF5 1.10.x Documentation

New Features in HDF5 1.10.0
Collective Metadata I/O


Fine-tuning the Metadata Cache

File Space Management

Virtual Datasets (VDS)

Partial Edge Chunks


Additional New APIs

New Features in HDF5 Release 1.10.0
New HDF5 Features

HDF5 Release 1.10.0 introduces several new features of the HDF5 Library. A brief description of each new feature and links to documentation for that feature appear below.

Due to the requirements of some of the new features, the format of a 1.10.x HDF5 file is likely to be different from that of a 1.8.x HDF5 file. This means that tools and applications built to read 1.10.x files will be able to read a 1.8.x file, but tools built to read 1.8.x files may not be able to read a 1.10.x file.

Data acquisition and computer modeling systems often need to analyze and visualize data while it is being written. It is not unusual, for example, for an application to produce results in the middle of a run that suggest some basic parameters be changed, sensors be adjusted, or the run be scrapped entirely.

To enable users to check on such systems, we have been developing a concurrent read/write file access pattern we call SWMR (pronounced swimmer). SWMR is short for single-writer/multiple-reader. SWMR functionality allows a writer process to add data to a file while multiple reader processes read from the file.

Fine-tuning the Metadata Cache
The orderly operation of the metadata cache is crucial to SWMR functioning. A number of APIs have been developed to handle the requests from writer and reader processes and to give applications the control of the metadata cache they might need. However, the metadata cache APIs can be used when SWMR is not being used; so, these functions are described separately.

Collective Metadata I/O
Calls for HDF5 metadata can result in many small reads and writes. On metadata reads, collective metadata I/O can improve performance by allowing the library to perform optimizations when reading the metadata, by having one rank read the data and broadcasting it to all other ranks.

Collective metadata I/O improves metadata write performance through the construction of an MPI derived datatype that is then written collectively in a single call.

File Space Management
Usage patterns when working with an HDF5 file sometimes result in wasted space within the file. This can also impair access times when working with the resulting files. The new file space management feature provides strategies for managing space in a file to improve performance in both of these arenas.

Virtual Datasets (VDS)
With a growing amount of data in HDF5, the need has emerged to access data stored across multiple HDF5 files using standard HDF5 objects, such as groups and datasets, without rewriting or rearranging the data. The new virtual dataset (VDS) feature enables an application to draw on multiple datasets and files to create virtual datasets without moving or rewriting any data.

Partial Edge Chunk Options
New options for the storage and filtering of partial edge chunks in a dataset provide a tool for tuning I/O speed and file size in cases where the dataset size may not be a multiple of the chunk size.

Additional New APIs
In addition to the features described above, several additional new functions, a new struct, and new macros have been introduced or newly versioned in this release.

For more information on these features, see the “User, Reference, and Design Documentation” section below.

Obtaining, Testing, and Experimenting with This Software

These features are now available in HDF5 Release 1.10.0, release on March 31, 2016. See Obtaining the Latest HDF5 Software.

Address any questions to the HDF Group Help Desk (email address below).

This release includes changes in the HDF5 storage format. These changes come into play when one or more of the new features listed above is used or when an application calls for use of the latest storage format (H5Pset_libver_bounds).

If an application built on HDF5 Release 1.10.0 avoids use of the new features and does not request use of the latest format, applications built on HDF5 Release 1.8.x will be able to read files the first application created. In addition, applications originally written for use with HDF5 Release 1.8.x can be linked against a suitably configured HDF5 Release 1.10.x library, thus taking advantage of performance improvements in 1.10.

User, Reference, and Design Documentation

Documentation for the new features of the HDF5 Library is available on the pages listed below.

Collective Metadata I/O The purpose of this page is to list and briefly describe the documentation available to those who will use the Collective Metadata I/O feature of the HDF5 Library.
Single-Writer/Multiple-Reader (SWMR) The purpose of this page is to list and briefly describe the documentation available to those who will use the Single-Writer/Multiple-Reader (SWMR) feature of the HDF5 Library.
Fine-tuning the Metadata Cache The purpose of this page is to list and briefly describe the documentation available to those who want to fine-tune how the metadata cache behaves.
File Space Management The purpose of this page is to list and briefly describe documentation for HDF5’s file space management capabilities.
Virtual Datasets (VDS) The purpose of this page is to list and briefly describe the documentation available to those who want to use the Virtual Datasets (VDS) feature of the HDF5 Library.
Partial Edge Chunks The purpose of this page is to briefly describe the new partial edge chunk options and to provide access to full descriptions for the relevant functions.
Reference The purpose of this page is to describe the changes made to HDF5 reference documents to support new features.
Additional New APIs This page lists various new functions, a new struct, and new macros that are either unrelated to other new features described elsewhere or have aspects that are unrelated to the feature where they are otherwise described.

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Last modified: 11 April 2016

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