Single-Writer/Multiple-Reader (SWMR)
Documentation
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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 found in the
HDF5 Library. The following are the sections
on this page:
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SWMR User’s Guide
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The
HDF5 Single-Writer/Multiple-Reader User’s Guide
describes HDF5’s SWMR feature and describes
how to use the feature. The feature allows concurrent access of HDF5
files by writer and reader processes.
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HDF5 Library APIs
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The APIs listed below will be incorporated into the
HDF5 Reference Manual when the SWMR feature
is fully released.
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H5Fstart_swmr_write |
Enables SWMR writing mode for a file. |
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H5DOappend |
Appends data to a dataset along a specified dimension. |
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H5Pget_append_flush
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Retrieves the values of the append property that is set up in the
dataset access property list.
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H5Pset_append_flush
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Sets two actions to perform when the size of a dataset’s
dimension being appended reaches a specified boundary.
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H5Pget_object_flush_cb
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Retrieves the object flush property values from the file access
property list.
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H5Pset_object_flush_cb
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Sets a callback function to invoke when an object flush occurs in
the file.
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H5Odisable_mdc_flushes
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Prevents metadata entries for an HDF5 object from being flushed from
the metadata cache to storage.
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H5Oenable_mdc_flushes
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Returns the cache entries associated with an HDF5 object to the
default metadata flush and eviction algorithm.
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H5Oare_mdc_flushes_disabled
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Determines if an HDF5 object (dataset, group, committed
datatype) has had flushes of metadata entries disabled.
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Tools
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The tools listed below will be incorporated into the
HDF5 Reference Manual when they are fully released.
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h5watch
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Allows users to output new records appended to a dataset as it
grows. In other words, this tool can be used to watch data that
is added to a dataset. The functionality is similar to the
Unix user command tail with the follow option, which
outputs appended data as the file grows.
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h5format_convert
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Allows users to convert the indexing type of a chunked dataset
made with a 1.10.x version of the HDF5 Library to the 1.8.x
version 1 B-tree indexing type.
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h5clear
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Allows users to clear the file consistency flags field in the
superblock of a file.
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SWMR Design Documents
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The SWMR design documents, listed below, describe how the feature
works and why design choices were made.
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Metadata Cache Issues under SWMR and their Solutions
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The HDF5 Library contains a cache that provides more efficient
access to HDF5 file metadata. Although helpful in most instances,
this cache can cause problems when the
single-writer/multiple-reader (SWMR) data access pattern is
used to access an HDF5 file. Additionally, there are even
deeper I/O issues that can affect HDF5 file metadata operations.
This document describes the cache-oriented problems that the
HDF5 Library must overcome in order to implement the SWMR
feature as well as our solutions.
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Improvements for SWMR File Access and Dataset Append
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This document describes changes to the HDF5 Library that improve the
SWMR (Single-Writer/Multiple-Reader) file access model and provide
better support for dataset append operations.
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HDF5 Single-Writer/Multiple-Reader Feature Design and Semantics
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This document describes the design and semantics of HDF5’s
single-writer/multiple-reader (SWMR) feature. This feature allows
multiple reader processes to inspect a file that is concurrently
being written to by a single writer process without requiring any
inter-process communication. |
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File Locking under SWMR – Semantics, Programming Model, and
Implementation
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This document describes the design and semantics of how file locking
is used to help prevent inappropriate concurrent file access. This
locking is only intended to help the user conform to SWMR semantics
and is not a fundamental part of SWMR synchronization.
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The HDF Group
