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HDF5 Road Map
October 15, 2008 HDF and HDF-EOS Workshop XII 2
Performance
Robustness
Ease of use
Innovation
October 15, 2008 HDF and HDF-EOS Workshop XII 3
Outline
• Performance improvements• Fortran 2003 features• HDF5 file recover (metadata journaling)
Performance Improvements in HDF5
• Examples of completed work:• New implementation of metadata cache to
improve I/O performance and memory usage when accessing many objects (HDF5 1.8.0)
• Faster, more scalable storage and access for large groups (HDF5 1.8.0)
October 15, 2008 HDF and HDF-EOS Workshop XII 5
Performance Improvements in HDF5
• Work in progress• New implementation of free-space management
• Affects “dynamic” applications that add/delete/modify existing objects
• When creating HDF5 objects, space is allocated from available space tracked by the free-space manager
• When deleting objects, unused space is added to the free-space pool via free-space manager
• Current implementation uses O(N2) operations for each N allocations or freeing space
• New implementation O(log2N)
October 15, 2008 HDF and HDF-EOS Workshop XII 6
Free-space Management
• Test: creating/deleting attributes• Create first set of attributes
• Delete odd-numbered attributes from the first set
• Create second set of attributes
• Delete all attributes from the second set
October 15, 2008 HDF and HDF-EOS Workshop XII 7
Number of attributes
Old implementation
New implementation
Improvement ratio
500 786.5 sec 68.2 sec 11.5x
1000 11000 sec 289 sec 38x
Performance Improvements in HDF5
• Work in progress• Fast data append (along slowest changing
dimension)
• Future areas of interest• Efficient chunking cache implementation
(NetCDF4)
• Efficient handling of the variable-length data including compression (will affect sizes of NPOESS files)
October 15, 2008 HDF and HDF-EOS Workshop XII 8
Status of the HDF5 Fortran Library
• HDF5 Fortran library is a part of standard HDF5 distribution
• First release goes back to 1999• Implemented as Fortran90 wrappers on top of the
HDF5 C library• Supported on Linux, Windows, Mac Intel, Solaris,
VMS, clusters, etc.• Compilers
• Open source gfortran, g95
• Vendors (SUN, Intel, PGI, Absoft)
• 32 and 64-bit versions
October 15, 2008 HDF and HDF-EOS Workshop XII 10
HDF5 Fortran Library
• Mimics HDF5 C APIs• Fortran 90 features used
• Modules
• Function overloading
• Function interfaces
• Dynamic memory allocation
• Optional parameters• Many Fortran APIs are simpler than their C
counterparts
October 15, 2008 HDF and HDF-EOS Workshop XII 11
Current Limitations
• Supports only “native” Fortran types such as• INTEGER
• REAL
• CHARACTER
• DOUBLE PRECISION (obsolete Fortran feature)
• No support for INTEGER*1, INTEGER*2, INTEGER*8, INTEGER*16, REAL*8, REAL*16• Cannot write/read buffers of those types
• Fortran types have to match C types• No support for –r8 and –r16 flags (Fortran real =/=
C float)
October 15, 2008 HDF and HDF-EOS Workshop XII 12
Current Limitations
• No support for INTEGER(KIND=n) and REAL(KIND=m)
• Integers n and m are called KIND parameters
• Returned byselected _int_kind (r)
-10r < n < 10r
selected_real_kind(p,r)
p – precision
r – decimal exponent range
October 15, 2008 HDF and HDF-EOS Workshop XII 13
Current Limitations
• Limited support for derived types (compare with C structures and HDF5 compound datatypes)• Supports derived types with “native” fields only
• Doesn’t support complex HDF5 datatypes
(e.g., with array member, or nested compound)
• Writes/reads HDF5 compound datasets by fields only
• Cannot be used in parallel applications
• No support for enum types
• No support for callback functions
October 15, 2008 HDF and HDF-EOS Workshop XII 14
Current Limitations - Summary
• Any application written according to Fortran 95/2003 standard will struggle using HDF5 Fortran Library
• Many HDF5 features are not available to Fortran applications
October 15, 2008 HDF and HDF-EOS Workshop XII 15
Fortran 2003 Features
• Fortran 2003 provides a standardized mechanism for interoperating with C• Module ISO_C_BINDING for interoperability of
intrinsic types
• C_PTR and C_FUNCPTR for interoperability with C pointers
• C_LOC(x) and C_FUNLOC(x) inquiry functions for getting addresses of variables and procedures
• BIND attribute for interoperability of derived types and C structures and enumerated types
October 15, 2008 HDF and HDF-EOS Workshop XII 16
Fortran 2003 Features and HDF5
• New 2003 features allowed us to support• Any Fortran INTEGER and REAL type data in
HDF5 files
• Fortran derived types and HDF5 compound datatypes
• Fortran enumerated types and HDF5 enumerated types
• HDF5 APIs with callbacks
October 15, 2008 HDF and HDF-EOS Workshop XII 17
Fortran Compilers with 2003 Features
Compiler Current versions and status of HDF5
Future versions
Intel Versions 10.1 and 11All F2003 functionality works in HDF5
Version 11 will have a fix that will allow us to remove common blocks
g95 August 2008 and later; All Fortran 2003 functionality works in HDF5
gfortran Version 4.4 Limited support for C interoperability; HDF5 doesn’t work
No plans from compiler developers to improve the support
SUN compilers Express-July 2008 build; HDF5 doesn’t work
No timeline for fixes; may be in a year
PGI Version 7.2.1; HDF5 doesn’t work
Fixes will be available in Version 8.
October 15, 2008 HDF and HDF-EOS Workshop XII 18
Example
October 15, 2008 HDF and HDF-EOS Workshop XII 21
HDF5 "SDScompound.h5" {GROUP "/" { DATASET "ArrayOfStructures" { DATATYPE H5T_COMPOUND { H5T_ARRAY { [13] H5T_STRING { STRSIZE 1; STRPAD H5T_STR_SPACEPAD; CSET H5T_CSET_ASCII; CTYPE H5T_C_S1; } } "chr_name"; H5T_STD_I8LE "a_name"; H5T_IEEE_F64LE "c_name"; H5T_IEEE_F32LE "b_name"; } …..
23
HDF5 file recovery orSurviving a System Failure
through Metadata Journaling
October 15, 2008 23HDF and HDF-EOS Workshop XII
October 15, 2008 HDF and HDF-EOS Workshop XII 2424
Surviving a System Failure in HDF5
• Problem:• Data in an opened HDF5 files susceptible to
corruption in the event of an application or system crash.
• Corruption possible if an opened HDF5 file has been updated when the crash occurs.
• Initial Objective:• Guarantee an HDF5 file with consistent metadata
can be reconstructed in the event of a crash.
• No guarantee on state of raw data – contains whatever made it to disk prior to crash.
October 15, 2008 HDF and HDF-EOS Workshop XII 2525
Crash Survivability in HDF5
• Approach: Metadata Journaling• When an HDF5 file is opened with Metadata
Journaling enabled, a companion Journal file is created.
• When an HDF5 API function that modifies metadata is completed, a transaction is recorded in the Journal file.
• If the application crashes, a recovery program can replay the journal by applying in order all metadata writes until the end of the last completed transaction written to the journal file.
Oct. 16 2008 HDF and HDF-EOS Workshop XII 26
Application crashed
HDF5 Metadata Journaling Recovery
RestoredHDF5 File
h5recover tool
liFe Corrupted 5DFH
Companion Journal File
October 15, 2008 HDF and HDF-EOS Workshop XII 2727
Implementation Status
• Serial HDF5 with synchronous write mode• Alpha1 released August 2008
• User interface (API definition and h5recover tool) and file format may change
October 15, 2008 HDF and HDF-EOS Workshop XII 2828
Metadata Journaling Plans
• Serial HDF5 with synchronous write mode• Finalize User interface definitions and file format
• Serial HDF5 with asynchronous write mode• To improve Journal file write speed
• More features (need funding)• Make raw data operations atomic
• Allow "super‐transactions" to be created by applications
• Enable journaling for Parallel HDF5
Acknowledgement
• This report is based upon work supported in part by a Cooperative Agreement with the National Aeronautics and Space Administration (NASA) under NASA Awards NNX06AC83A and NNX08AO77A. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.
October 16, 2008 30HDF and HDF-EOS Workshop XII