[R] [R-pkgs] major release ff 2.0 (large atomic objects)

[Jens Oehlschlägel]

Dear R community,

ff Version 2.0 is available on CRAN. Based on paging concepts from version 1.0, 
2.0 is a major redesign of this package for handling large datasets. 
We have implemented numerous enhancements and performance improvements to make 
this package suitable as a 'base' package for large data processing. 

The ff package provides atomic data structures that are stored on disk but 
behave (almost) as if they were in RAM by transparently mapping only a section 
(pagesize) in main memory - the effective virtual memory consumption per ff 
object.

In addition to the 'double' data type, ff objects now have support for
'logical', 'raw' and 'integer' atomic datatypes, plus close-to-atomic types 
like 'factor', 'POSIXct' or custom close-to-atomic types. In addition to fast 
vector access, ff now has native support for matrices and arrays with flexible 
dimorder (major column-order, major row-order and generalizations for arrays). 

While the raw data still gets stored on binary flat files in native encoding,
'ff' objects have been extended to carry their meta information as physical
and virtual attributes. ff objects have well-defined hybrid copying semantics, 
which gives rise to certain performance improvements through virtualization. 

The new ff objects can be stored and reopened across R sessions. Flat files can 
be shared by multiple 'ff' R objects (using different data en/de-coding 
schemes) in the same process or from multiple R processes to exploit 
parallelism. A wide choice of finalizer options allows to work with 'permanent'
files as well as creating/removing 'temporary' ff files completely transparent 
to the user. On certain OS/Filesystem combinations, the creation process of 
large atomic data sets has been speed-up dramatically using sparse file 
allocation.

Several access optimization techniques such as Hybrid Index Preprocessing and 
Virtualization are implemented to achieve good performance even with large 
datasets, for example virtual matrix transpose without touching a single byte 
on disk.

Further, to reduce disk I/O, the atomic data gets stored native and compact on
binary flat files i.e. logicals take up exactly 2 bits to represent TRUE, FALSE
and NA.

Beyond basic access functions, the ff package also provides compatibility 
functions that facilitate writing code for ff and ram objects and support for 
batch processing on ff objects (e.g. as.ram, as.ff, ffapply).

A package that supports convenient processing of large ff objects is in the 
making. R.ff will make the bigger part of R's basic functions available for ff 
objects through method dispatch and/or an evaluator that handles expressions 
which contain ff objects. 

NOTE: A professional extension is available from the authors, which integrates
      additional high-performance features neatly into the ff package. 
      The extension allows  efficient handling of symmetric matrices 
      and supports more packed data types: 
      boolean (1 bit), quad (2 bit unsigned), nibble (4 bit unsigned)
      , byte (1 byte signed with NAs), ubyte (1 byte unsigned)
      , short (2 byte signed with NAs), ushort (2 byte unsigned)
      , single (4 byte float with NAs). 
      For example 'quad' allows efficient storage of genomic data as an 
      'A','T','G','C' factor. The unsigned types support 'circular' arithmetic. 
 
P.S. If you are interested in ff 2.0 you might want to visit our presentation 
August 5th at JSM "High-Performance Processing of Large Data Sets via Memory 
Mapping: A Case Study in R And C++" or the official package presentation at 
UseR!2008 in Dortmund scheduled for August 13th. 

The ff authors
Daniel Adler <dadler at uni-goettingen.de>
Christian Gläser <christian_glaeser at gmx.de>
Oleg Nenadic <onenadi at uni-goettingen.de>
Jens Oehlschlägel <Jens.Oehlschlaegel at truecluster.com>
Walter Zucchini <wzucchi at uni-goettingen.de>

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