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Signed-off-by: Daniel Baumann <daniel@debian.org>
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doc/plzip.texi
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@ -6,8 +6,8 @@
@finalout
@c %**end of header
@set UPDATED 12 April 2017
@set VERSION 1.6
@set UPDATED 7 February 2018
@set VERSION 1.7
@dircategory Data Compression
@direntry
@ -36,6 +36,7 @@ This manual is for Plzip (version @value{VERSION}, @value{UPDATED}).
@menu
* Introduction:: Purpose and features of plzip
* Output:: Meaning of plzip's output
* Invoking plzip:: Command line interface
* Program design:: Internal structure of plzip
* File format:: Detailed format of the compressed file
@ -48,7 +49,7 @@ This manual is for Plzip (version @value{VERSION}, @value{UPDATED}).
@end menu
@sp 1
Copyright @copyright{} 2009-2017 Antonio Diaz Diaz.
Copyright @copyright{} 2009-2018 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission
to copy, distribute and modify it.
@ -81,7 +82,7 @@ availability:
The lzip format provides very safe integrity checking and some data
recovery means. The
@uref{http://www.nongnu.org/lzip/manual/lziprecover_manual.html#Data-safety,,lziprecover}
program can repair bit-flip errors (one of the most common forms of data
program can repair bit flip errors (one of the most common forms of data
corruption) in lzip files, and provides data recovery capabilities,
including error-checked merging of damaged copies of a file.
@ifnothtml
@ -143,9 +144,54 @@ incomprehensible and therefore pointless.
Plzip will correctly decompress a file which is the concatenation of two
or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
corresponding decompressed files. Integrity testing of concatenated
compressed files is also supported.
@node Output
@chapter Meaning of plzip's output
@cindex output
The output of plzip looks like this:
@example
plzip -v foo
foo: 6.676:1, 14.98% ratio, 85.02% saved, 450560 in, 67493 out.
plzip -tvv foo.lz
foo.lz: 6.676:1, 14.98% ratio, 85.02% saved. ok
@end example
The meaning of each field is as follows:
@table @code
@item N:1
The compression ratio @w{(uncompressed_size / compressed_size)}, shown
as N to 1.
@item ratio
The inverse compression ratio @w{(compressed_size / uncompressed_size)},
shown as a percentage. A decimal ratio is easily obtained by moving the
decimal point two places to the left; @w{14.98% = 0.1498}.
@item saved
The space saved by compression @w{(1 - ratio)}, shown as a percentage.
@item in
The size of the uncompressed data. When decompressing or testing, it is
shown as @code{decompressed}. Note that plzip always prints the
uncompressed size before the compressed size when compressing,
decompressing, testing or listing.
@item out
The size of the compressed data. When decompressing or testing, it is
shown as @code{compressed}.
@end table
When decompressing or testing at verbosity level 4 (-vvvv), the
dictionary size used to compress the file is also shown.
LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never
have been compressed. Decompressed is used to refer to data which have
undergone the process of decompression.
@ -169,7 +215,7 @@ plzip [@var{options}] [@var{files}]
mixed with other @var{files} and is read just once, the first time it
appears in the command line.
Plzip supports the following options:
plzip supports the following options:
@table @code
@item -h
@ -190,12 +236,12 @@ garbage that can be safely ignored. @xref{concat-example}.
@anchor{--data-size}
@item -B @var{bytes}
@itemx --data-size=@var{bytes}
Set the size of the input data blocks, in bytes. The input file will be
divided in chunks of this size before compression is performed. Valid
values range from 8 KiB to 1 GiB. Default value is two times the
dictionary size, except for option @samp{-0} where it defaults to 1 MiB.
Plzip will reduce the dictionary size if it is larger than the chosen
data size.
When compressing, set the size of the input data blocks in bytes. The
input file will be divided in chunks of this size before compression is
performed. 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}. Plzip will reduce the dictionary size if it is
larger than the chosen data size.
@item -c
@itemx --stdout
@ -206,10 +252,10 @@ device.
@item -d
@itemx --decompress
Decompress the specified file(s). If a file does not exist or can't be
Decompress the specified files. If a file does not exist or can't be
opened, plzip continues decompressing the rest of the files. If a file
fails to decompress, plzip exits immediately without decompressing the
rest of the files.
fails to decompress, or is a terminal, plzip exits immediately without
decompressing the rest of the files.
@item -f
@itemx --force
@ -217,8 +263,8 @@ Force overwrite of output files.
@item -F
@itemx --recompress
Force re-compression of files whose name already has the @samp{.lz} or
@samp{.tlz} suffix.
When compressing, force re-compression of files whose name already has
the @samp{.lz} or @samp{.tlz} suffix.
@item -k
@itemx --keep
@ -227,7 +273,7 @@ Keep (don't delete) input files during compression or decompression.
@item -l
@itemx --list
Print the uncompressed size, compressed size and percentage saved of the
specified file(s). Trailing data are ignored. The values produced are
specified files. Trailing data are ignored. The values produced are
correct even for multimember files. If more than one file is given, a
final line containing the cumulative sizes is printed. With @samp{-v},
the dictionary size, the number of members in the file, and the amount
@ -240,16 +286,21 @@ verifies that none of the specified files contain trailing data.
@item -m @var{bytes}
@itemx --match-length=@var{bytes}
Set the match length limit in bytes. After a match this long is found,
the search is finished. Valid values range from 5 to 273. Larger values
usually give better compression ratios but longer compression times.
When compressing, set the match length limit in bytes. After a match
this long is found, the search is finished. Valid values range from 5 to
273. Larger values usually give better compression ratios but longer
compression times.
@item -n @var{n}
@itemx --threads=@var{n}
Set the number of worker threads. Valid values range from 1 to "as many
as your system can support". If this option is not used, plzip tries to
detect the number of processors in the system and use it as default
value. @w{@samp{plzip --help}} shows the system's default value.
Set the number of worker threads, overriding the system's default. Valid
values range from 1 to "as many as your system can support". If this
option is not used, plzip tries to detect the number of processors in
the system and use it as default value. When compressing on a @w{32 bit}
system, plzip tries to limit the memory use to under @w{2.22 GiB} (4
worker threads at level -9) by reducing the number of threads below the
system's default. @w{@samp{plzip --help}} shows the system's default
value.
Note that the number of usable threads is limited to @w{ceil( file_size
/ data_size )} during compression (@pxref{Minimum file sizes}), and to
@ -260,7 +311,9 @@ the number of members in the input during decompression.
When reading from standard input and @samp{--stdout} has not been
specified, use @samp{@var{file}} as the virtual name of the uncompressed
file. This produces a file named @samp{@var{file}} when decompressing,
and a file named @samp{@var{file}.lz} when compressing.
or a file named @samp{@var{file}.lz} when compressing. A second
@samp{.lz} extension is not added if @samp{@var{file}} already ends in
@samp{.lz} or @samp{.tlz}.
@item -q
@itemx --quiet
@ -268,12 +321,12 @@ Quiet operation. Suppress all messages.
@item -s @var{bytes}
@itemx --dictionary-size=@var{bytes}
Set the dictionary size limit in bytes. Plzip will use the smallest
possible dictionary size for each file without exceeding this limit.
Valid values range from 4 KiB to 512 MiB. Values 12 to 29 are
interpreted as powers of two, meaning 2^12 to 2^29 bytes. Note that
dictionary sizes are quantized. If the specified size does not match one
of the valid sizes, it will be rounded upwards by adding up to
When compressing, set the dictionary size limit in bytes. Plzip will use
the smallest possible dictionary size for each file without exceeding
this limit. Valid values range from @w{4 KiB} to @w{512 MiB}. Values 12
to 29 are interpreted as powers of two, meaning 2^12 to 2^29 bytes. Note
that dictionary sizes are quantized. If the specified size does not
match one of the valid sizes, it will be rounded upwards by adding up to
@w{(@var{bytes} / 8)} to it.
For maximum compression you should use a dictionary size limit as large
@ -282,27 +335,29 @@ is affected at compression time by the choice of dictionary size limit.
@item -t
@itemx --test
Check integrity of the specified file(s), but don't decompress them.
This really performs a trial decompression and throws away the result.
Use it together with @samp{-v} to see information about the file(s). If
a file does not exist, can't be opened, or is a terminal, plzip
continues checking the rest of the files. If a file fails the test,
plzip may be unable to check the rest of the files.
Check integrity of the specified files, but don't decompress them. This
really performs a trial decompression and throws away the result. Use it
together with @samp{-v} to see information about the files. If a file
does not exist, can't be opened, or is a terminal, plzip continues
checking the rest of the files. If a file fails the test, plzip may be
unable to check the rest of the files.
@item -v
@itemx --verbose
Verbose mode.@*
When compressing, show the compression ratio for each file processed. A
second @samp{-v} shows the progress of compression.@*
When compressing, show the compression ratio and size for each file
processed.@*
When decompressing or testing, further -v's (up to 4) increase the
verbosity level, showing status, compression ratio, dictionary size,
decompressed size, and compressed size.
decompressed size, and compressed size.@*
Two or more @samp{-v} options show the progress of (de)compression,
except for single-member files.
@item -0 .. -9
Set the compression parameters (dictionary size and match length limit)
as shown in the table below. The default compression level is @samp{-6}.
Note that @samp{-9} can be much slower than @samp{-0}. These options
have no effect when decompressing.
have no effect when decompressing, testing or listing.
The bidimensional parameter space of LZMA can't be mapped to a linear
scale optimal for all files. If your files are large, very repetitive,
@ -327,6 +382,12 @@ etc, you may need to use the @samp{--dictionary-size} and
@itemx --best
Aliases for GNU gzip compatibility.
@item --loose-trailing
When decompressing, testing or listing, allow trailing data whose first
bytes are so similar to the magic bytes of a lzip header that they can
be confused with a corrupt header. Use this option if a file triggers a
"corrupt header" error and the cause is not indeed a corrupt header.
@end table
Numbers given as arguments to options may be followed by a multiplier
@ -363,8 +424,8 @@ creating a multimember compressed file.
When decompressing, plzip decompresses as many members simultaneously as
worker threads are chosen. Files that were compressed with lzip will not
be decompressed faster than using lzip (unless the @samp{-b} option was
used) because lzip usually produces single-member files, which can't be
be decompressed faster than using lzip (unless the @samp{-b} option was used)
because lzip usually produces single-member files, which can't be
decompressed in parallel.
For each input file, a splitter thread and several worker threads are
@ -377,6 +438,19 @@ to the workers. The workers (de)compress the blocks received from the
splitter. The muxer collects processed packets from the workers, and
writes them to the output file.
@verbatim
,------------,
,-->| worker 0 |--,
| `------------' |
,-------, ,----------, | ,------------, | ,-------, ,--------,
| input |-->| splitter |-+-->| worker 1 |--+-->| muxer |-->| output |
| file | `----------' | `------------' | `-------' | file |
`-------' | ... | `--------'
| ,------------, |
`-->| worker N-1 |--'
`------------'
@end verbatim
When decompressing from a regular file, the splitter is removed and the
workers read directly from the input file. If the output file is also a
regular file, the muxer is also removed and the workers write directly
@ -472,35 +546,60 @@ facilitates safe recovery of undamaged members from multimember files.
@chapter Memory required to compress and decompress
@cindex memory requirements
The amount of memory required @strong{per thread} is approximately the
following:
The amount of memory required @strong{per thread} for decompression or
testing is approximately the following:
@itemize @bullet
@item
For compression at level -0; 1.5 MiB plus 3 times the data size
(@pxref{--data-size}). Default is 4.5 MiB.
@item
For compression at other levels; 11 times the dictionary size plus 3
times the data size. Default is 136 MiB.
@item
For decompression of a regular (seekable) file to another regular file,
or for testing of a regular file; the dictionary size.
@item
For testing of a non-seekable file or of standard input; the dictionary
size plus up to 5 MiB.
size plus up to @w{5 MiB}.
@item
For decompression of a regular file to a non-seekable file or to
standard output; the dictionary size plus up to 32 MiB.
standard output; the dictionary size plus up to @w{32 MiB}.
@item
For decompression of a non-seekable file or of standard input; the
dictionary size plus up to 35 MiB.
dictionary size plus up to @w{35 MiB}.
@end itemize
@noindent
The amount of memory required @strong{per thread} for compression is
approximately the following:
@itemize @bullet
@item
For compression at level -0; @w{1.5 MiB} plus 3.375 times the data size
(@pxref{--data-size}). Default is @w{4.875 MiB}.
@item
For compression at other levels; 11 times the dictionary size plus 3.375
times the data size. Default is @w{142 MiB}.
@end itemize
@noindent
The following table shows the memory required @strong{per thread} for
compression at a given level, using the default data size for each
level:
@multitable {Level} {Memory required}
@item Level @tab Memory required
@item -0 @tab 4.875 MiB
@item -1 @tab 17.75 MiB
@item -2 @tab 26.625 MiB
@item -3 @tab 35.5 MiB
@item -4 @tab 53.25 MiB
@item -5 @tab 71 MiB
@item -6 @tab 142 MiB
@item -7 @tab 284 MiB
@item -8 @tab 426 MiB
@item -9 @tab 568 MiB
@end multitable
@node Minimum file sizes
@chapter Minimum file sizes required for full compression speed
@ -516,7 +615,8 @@ least as large as the number of worker threads times the chunk 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{(file_size / data_size)}.
@w{(file_size / data_size)}. For example, a tarball the size of gcc or
linux will scale up to 8 processors at level -9.
The following table shows the minimum uncompressed file size needed for
full use of N processors at a given compression level, using the default
@ -554,9 +654,10 @@ padding zero bytes to a lzip file.
@item
Useful data added by the user; a cryptographically secure hash, a
description of file contents, etc. It is safe to append any amount of
text to a lzip file as long as the text does not begin with the string
"LZIP", and does not contain any zero bytes (null characters). Nonzero
bytes and zero bytes can't be safely mixed in trailing data.
text to a lzip file as long as none of the first four bytes of the text
match the corresponding byte in the string "LZIP", and the text does not
contain any zero bytes (null characters). Nonzero bytes and zero bytes
can't be safely mixed in trailing data.
@item
Garbage added by some not totally successful copy operation.
@ -566,12 +667,16 @@ Malicious data added to the file in order to make its total size and
hash value (for a chosen hash) coincide with those of another file.
@item
In very rare cases, trailing data could be the corrupt header of another
In rare cases, trailing data could be the corrupt header of another
member. In multimember or concatenated files the probability of
corruption happening in the magic bytes is 5 times smaller than the
probability of getting a false positive caused by the corruption of the
integrity information itself. Therefore it can be considered to be below
the noise level.
the noise level. Additionally, the test used by plzip to discriminate
trailing data from a corrupt header has a Hamming distance (HD) of 3,
and the 3 bit flips must happen in different magic bytes for the test to
fail. In any case, the option @samp{--trailing-error} guarantees that
any corrupt header will be detected.
@end itemize
Trailing data are in no way part of the lzip file format, but tools
@ -607,7 +712,7 @@ plzip -v file
@sp 1
@noindent
Example 2: Like example 1 but the created @samp{file.lz} has a block
size of 1 MiB. The compression ratio is not shown.
size of @w{1 MiB}. The compression ratio is not shown.
@example
plzip -B 1MiB file
@ -656,7 +761,7 @@ Do this instead
@sp 1
@noindent
Example 7: Decompress @samp{file.lz} partially until 10 KiB of
Example 7: Decompress @samp{file.lz} partially until @w{10 KiB} of
decompressed data are produced.
@example