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diff --git a/doc/tarlz.texi b/doc/tarlz.texi index 2ab37fb..6026fe3 100644 --- a/doc/tarlz.texi +++ b/doc/tarlz.texi @@ -6,8 +6,8 @@ @finalout @c %**end of header -@set UPDATED 31 January 2019 -@set VERSION 0.10 +@set UPDATED 13 February 2019 +@set VERSION 0.11 @dircategory Data Compression @direntry @@ -40,6 +40,7 @@ This manual is for Tarlz (version @value{VERSION}, @value{UPDATED}). * File format:: Detailed format of the compressed archive * Amendments to pax format:: The reasons for the differences with pax * Multi-threaded tar:: Limitations of parallel tar decoding +* Minimum archive sizes:: Sizes required for full multi-threaded speed * Examples:: A small tutorial with examples * Problems:: Reporting bugs * Concept index:: Index of concepts @@ -56,25 +57,24 @@ to copy, distribute and modify it. @chapter Introduction @cindex introduction -@uref{http://www.nongnu.org/lzip/tarlz.html,,Tarlz} is a combined -implementation of the tar archiver and the -@uref{http://www.nongnu.org/lzip/lzip.html,,lzip} compressor. By default -tarlz creates, lists and extracts archives in a simplified posix pax format -compressed with lzip on a per file basis. Each tar member is compressed in -its own lzip member, as well as the end-of-file blocks. This method adds an -indexed lzip layer on top of the tar archive, making it possible to decode -the archive safely in parallel. The resulting multimember tar.lz archive is -fully backward compatible with standard tar tools like GNU tar, which treat -it like any other tar.lz archive. Tarlz can append files to the end of such -compressed archives. - -Tarlz can create tar archives with four levels of compression granularity; -per file, per directory, appendable solid, and solid. +@uref{http://www.nongnu.org/lzip/tarlz.html,,Tarlz} is a massively parallel +(multi-threaded) combined implementation of the tar archiver and the +@uref{http://www.nongnu.org/lzip/lzip.html,,lzip} compressor. Tarlz creates, +lists and extracts archives in a simplified posix pax format compressed with +lzip, keeping the alignment between tar members and lzip members. This +method adds an indexed lzip layer on top of the tar archive, making it +possible to decode the archive safely in parallel. The resulting multimember +tar.lz archive is fully backward compatible with standard tar tools like GNU +tar, which treat it like any other tar.lz archive. Tarlz can append files to +the end of such compressed archives. + +Tarlz can create tar archives with five levels of compression granularity; +per file, per block, per directory, appendable solid, and solid. @noindent -Of course, compressing each file (or each directory) individually is -less efficient than compressing the whole tar archive, but it has the -following advantages: +Of course, compressing each file (or each directory) individually can't +achieve a compression ratio as high as compressing solidly the whole tar +archive, but it has the following advantages: @itemize @bullet @item @@ -120,18 +120,23 @@ tarlz [@var{options}] [@var{files}] @end example @noindent -On archive creation or appending, tarlz removes leading and trailing -slashes from filenames, as well as filename prefixes containing a -@samp{..} component. On extraction, archive members containing a -@samp{..} component are skipped. Tarlz detects when the archive being -created or enlarged is among the files to be dumped, appended or -concatenated, and skips it. +On archive creation or appending tarlz archives the files specified, but +removes from member names any leading and trailing slashes and any filename +prefixes containing a @samp{..} component. On extraction, leading and +trailing slashes are also removed from member names, and archive members +containing a @samp{..} component in the filename are skipped. Tarlz detects +when the archive being created or enlarged is among the files to be dumped, +appended or concatenated, and skips it. On extraction and listing, tarlz removes leading @samp{./} strings from member names in the archive or given in the command line, so that @w{@code{tarlz -xf foo ./bar baz}} extracts members @samp{bar} and @samp{./baz} from archive @samp{foo}. +If several compression levels or @samp{--*solid} options are given, the last +setting is used. For example @w{@samp{-9 --solid --uncompressed -1}} is +equivalent to @samp{-1 --solid} + tarlz supports the following options: @table @code @@ -160,6 +165,7 @@ specified. Tarlz can't concatenate uncompressed tar archives. Set target size of input data blocks for the @samp{--bsolid} option. Valid values range from @w{8 KiB} to @w{1 GiB}. Default value is two times the dictionary size, except for option @samp{-0} where it defaults to @w{1 MiB}. +@xref{Minimum archive sizes}. @item -c @itemx --create @@ -176,6 +182,10 @@ extraction. Listing ignores any @samp{-C} options specified. @var{dir} is relative to the then current working directory, perhaps changed by a previous @samp{-C} option. +Note that a process can only have one current working directory (CWD). +Therefore multi-threading can't be used to create an archive if a @samp{-C} +option appears after a relative filename in the command line. + @item -f @var{archive} @itemx --file=@var{archive} Use archive file @var{archive}. @samp{-} used as an @var{archive} @@ -183,17 +193,19 @@ argument reads from standard input or writes to standard output. @item -n @var{n} @itemx --threads=@var{n} -Set the number of decompression threads, overriding the system's default. +Set the number of (de)compression threads, overriding the system's default. Valid values range from 0 to "as many as your system can support". A value of 0 disables threads entirely. If this option is not used, tarlz tries to detect the number of processors in the system and use it as default value. -@w{@samp{tarlz --help}} shows the system's default value. This option -currently only has effect when listing the contents of a multimember -compressed archive. @xref{Multi-threaded tar}. +@w{@samp{tarlz --help}} shows the system's default value. See the note about +multi-threaded archive creation in the @samp{-C} option above. +Multi-threaded extraction of files from an archive is not yet implemented. +@xref{Multi-threaded tar}. -Note that the number of usable threads is limited during decompression to -the number of lzip members in the tar.lz archive, which you can find by -running @w{@code{lzip -lv archive.tar.lz}}. +Note that the number of usable threads is limited during compression to +@w{ceil( uncompressed_size / data_size )} (@pxref{Minimum archive sizes}), +and during decompression to the number of lzip members in the tar.lz +archive, which you can find by running @w{@code{lzip -lv archive.tar.lz}}. @item -q @itemx --quiet @@ -213,7 +225,7 @@ to an uncompressed tar archive. @item -t @itemx --list List the contents of an archive. If @var{files} are given, list only the -given @var{files}. +@var{files} given. @item -v @itemx --verbose @@ -222,7 +234,7 @@ Verbosely list files processed. @item -x @itemx --extract Extract files from an archive. If @var{files} are given, extract only -the given @var{files}. Else extract all the files in the archive. +the @var{files} given. Else extract all the files in the archive. @item -0 .. -9 Set the compression level. The default compression level is @samp{-6}. @@ -245,40 +257,42 @@ it creates, reducing the amount of memory required for decompression. @item --asolid When creating or appending to a compressed archive, use appendable solid -compression. All the files being added to the archive are compressed -into a single lzip member, but the end-of-file blocks are compressed -into a separate lzip member. This creates a solidly compressed -appendable archive. +compression. All the files being added to the archive are compressed into a +single lzip member, but the end-of-file blocks are compressed into a +separate lzip member. This creates a solidly compressed appendable archive. +Solid archives can't be created nor decoded in parallel. @item --bsolid -When creating or appending to a compressed archive, compress tar members -together in a lzip member until they approximate a target uncompressed size. -The size can't be exact because each solidly compressed data block must -contain an integer number of tar members. This option improves compression -efficiency for archives with lots of small files. @xref{--data-size}, to set -the target block size. +When creating or appending to a compressed archive, use block compression. +Tar members are compressed together in a lzip member until they approximate +a target uncompressed size. The size can't be exact because each solidly +compressed data block must contain an integer number of tar members. Block +compression is the default because it improves compression ratio for +archives with many files smaller than the block size. This option allows +tarlz revert to default behavior if, for example, it is invoked through an +alias like @code{tar='tarlz --solid'}. @xref{--data-size}, to set the target +block size. @item --dsolid -When creating or appending to a compressed archive, use solid -compression for each directory especified in the command line. The -end-of-file blocks are compressed into a separate lzip member. This -creates a compressed appendable archive with a separate lzip member for -each top-level directory. +When creating or appending to a compressed archive, compress each file +specified in the command line separately in its own lzip member, and use +solid compression for each directory specified in the command line. The +end-of-file blocks are compressed into a separate lzip member. This creates +a compressed appendable archive with a separate lzip member for each file or +top-level directory specified. @item --no-solid When creating or appending to a compressed archive, compress each file -separately. The end-of-file blocks are compressed into a separate lzip -member. This creates a compressed appendable archive with a separate -lzip member for each file. This option allows tarlz revert to default -behavior if, for example, tarlz is invoked through an alias like -@code{tar='tarlz --solid'}. +separately in its own lzip member. The end-of-file blocks are compressed +into a separate lzip member. This creates a compressed appendable archive +with a lzip member for each file. @item --solid -When creating or appending to a compressed archive, use solid -compression. The files being added to the archive, along with the -end-of-file blocks, are compressed into a single lzip member. The -resulting archive is not appendable. No more files can be later appended -to the archive. +When creating or appending to a compressed archive, use solid compression. +The files being added to the archive, along with the end-of-file blocks, are +compressed into a single lzip member. The resulting archive is not +appendable. No more files can be later appended to the archive. Solid +archives can't be created nor decoded in parallel. @item --anonymous Equivalent to @samp{--owner=root --group=root}. @@ -388,11 +402,11 @@ binary zeros, interpreted as an end-of-archive indicator. These EOF blocks are either compressed in a separate lzip member or compressed along with the tar members contained in the last lzip member. -The diagram below shows the correspondence between each tar member -(formed by one or two headers plus optional data) in the tar archive and -each +The diagram below shows the correspondence between each tar member (formed +by one or two headers plus optional data) in the tar archive and each @uref{http://www.nongnu.org/lzip/manual/lzip_manual.html#File-format,,lzip member} -in the resulting multimember tar.lz archive: +in the resulting multimember tar.lz archive, when per file compression is +used: @ifnothtml @xref{File format,,,lzip}. @end ifnothtml @@ -672,10 +686,10 @@ format. @section Avoid misconversions to/from UTF-8 There is no portable way to tell what charset a text string is coded into. -Therefore, tarlz stores all fields representing text strings as-is, without -conversion to UTF-8 nor any other transformation. This prevents accidental -double UTF-8 conversions. If the need arises this behavior will be adjusted -with a command line option in the future. +Therefore, tarlz stores all fields representing text strings unmodified, +without conversion to UTF-8 nor any other transformation. This prevents +accidental double UTF-8 conversions. If the need arises this behavior will +be adjusted with a command line option in the future. @node Multi-threaded tar @@ -717,13 +731,51 @@ it only needs to decompress part of each lzip member. See the following example listing the Silesia corpus on a dual core machine: @example -tarlz -9 -cf silesia.tar.lz silesia +tarlz -9 --no-solid -cf silesia.tar.lz silesia time lzip -cd silesia.tar.lz | tar -tf - (5.032s) time plzip -cd silesia.tar.lz | tar -tf - (3.256s) time tarlz -tf silesia.tar.lz (0.020s) @end example +@node Minimum archive sizes +@chapter Minimum archive sizes required for multi-threaded block compression +@cindex minimum archive sizes + +When creating or appending to a compressed archive using multi-threaded +block compression, tarlz puts tar members together in blocks and compresses +as many blocks simultaneously as worker threads are chosen, creating a +multimember compressed archive. + +For this to work as expected (and roughly multiply the compression speed by +the number of available processors), the uncompressed archive must be at +least as large as the number of worker threads times the block size +(@pxref{--data-size}). Else some processors will not get any data to +compress, and compression will be proportionally slower. The maximum speed +increase achievable on a given file is limited by the ratio +@w{(uncompressed_size / data_size)}. For example, a tarball the size of gcc +or linux will scale up to 10 or 12 processors at level -9. + +The following table shows the minimum uncompressed archive size needed for +full use of N processors at a given compression level, using the default +data size for each level: + +@multitable {Processors} {512 MiB} {512 MiB} {512 MiB} {512 MiB} {512 MiB} {512 MiB} +@headitem Processors @tab 2 @tab 4 @tab 8 @tab 16 @tab 64 @tab 256 +@item Level +@item -0 @tab 2 MiB @tab 4 MiB @tab 8 MiB @tab 16 MiB @tab 64 MiB @tab 256 MiB +@item -1 @tab 4 MiB @tab 8 MiB @tab 16 MiB @tab 32 MiB @tab 128 MiB @tab 512 MiB +@item -2 @tab 6 MiB @tab 12 MiB @tab 24 MiB @tab 48 MiB @tab 192 MiB @tab 768 MiB +@item -3 @tab 8 MiB @tab 16 MiB @tab 32 MiB @tab 64 MiB @tab 256 MiB @tab 1 GiB +@item -4 @tab 12 MiB @tab 24 MiB @tab 48 MiB @tab 96 MiB @tab 384 MiB @tab 1.5 GiB +@item -5 @tab 16 MiB @tab 32 MiB @tab 64 MiB @tab 128 MiB @tab 512 MiB @tab 2 GiB +@item -6 @tab 32 MiB @tab 64 MiB @tab 128 MiB @tab 256 MiB @tab 1 GiB @tab 4 GiB +@item -7 @tab 64 MiB @tab 128 MiB @tab 256 MiB @tab 512 MiB @tab 2 GiB @tab 8 GiB +@item -8 @tab 96 MiB @tab 192 MiB @tab 384 MiB @tab 768 MiB @tab 3 GiB @tab 12 GiB +@item -9 @tab 128 MiB @tab 256 MiB @tab 512 MiB @tab 1 GiB @tab 4 GiB @tab 16 GiB +@end multitable + + @node Examples @chapter A small tutorial with examples @cindex examples |