2021-09-02 05:09:27 +08:00
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/** \page Files
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2022-12-21 06:59:40 +08:00
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\section secFiles Files
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2021-09-02 05:09:27 +08:00
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\subsection CB_FreeSpace Tracking Free Space in HDF5 Files
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\par Problem
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You sometimes delete objects in HDF5 files and don't have new content to use the
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free space, but would like to reuse it in the future.
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\par Solution
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At file creation time, set the file space management strategy and persistence of
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free space tracking information via H5Pset_file_space_strategy().
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\note This feature is only supported in HDF5 1.10.1+.
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\snippet{lineno} Files.c free_space
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\par Discussion
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Free space tracking is supported only in HDF5 versions 1.10.x and higher.
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This has implications for the accessibility of your HDF5 files and
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should be considered carefully. If compatibility with previous versions of
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HDF5 must be maintained, space reclamation via \Code{h5repack} might be an option.\n
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The file space strategy #H5F_FSPACE_STRATEGY_FSM_AGGR is not the only option
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that supports free-space tracking. #H5F_FSPACE_STRATEGY_PAGE is another option,
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which adds paged allocation and is used most effectively with page buffering.\n
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For an in-depth account of HDF5 file space management, paged-allocation, and
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page buffering, see the following documents:
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\li \ref_rfc20121024
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\li \ref_rfc20120523
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\li \ref_rfc20150709
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\par See Also
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See \ref CB_MaintainCompat for HDF5 compatibility implications.
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\subsection CB_RemoveUnusedSpace Removing Unused Space from HDF5 Files
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\par Problem
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Based on estimates or \Code{h5stat} output you know that a large portion
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of an HDF5 file consists of free or unaccounted space, and you would like
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to remove it.
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\subsection CB_UserBlock Creating an HDF5 File User Block
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\par Problem
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You would like to include certain ancillary, non-HDF5 content in an
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HDF5 file such that it can be accessed without the HDF5 library.
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\par Solution
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Use a file creation property list in which the user block size is set via
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H5Pset_userblock(). In the example below, we create an 8 MiB user block.
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\snippet{lineno} Files.c user_block
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\par Discussion
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The user block begins at offset 0 and must be at least 512 bytes and a power
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of 2. The HDF5 library ignores any content between the beginning of the
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file and the end of the user block.\n
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You can add or strip a user block to/from an existing HDF5 file with the
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\Code{h5jam}/\Code{h5unjam} tool, respectively.
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\warning
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If you try to embed content into the user block for use by other applications,
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pay close attention to how they handle space beyond the last used byte in the
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user block or the user block in general. In the worst case, applications might
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try to truncate the rest of the file and destroy the HDF5 portion of the file.
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\par See Also
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References to related recipes
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*/
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