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xz: Update the man page about --block-size.

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Lasse Collin 2014-12-16 20:57:43 +02:00
parent 7dddfbeb49
commit 009823448b
1 changed files with 33 additions and 8 deletions
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@ -5,7 +5,7 @@
.\" This file has been put into the public domain.
.\" You can do whatever you want with this file.
.\"
.TH XZ 1 "2013-11-12" "Tukaani" "XZ Utils"
.TH XZ 1 "2014-12-16" "Tukaani" "XZ Utils"
.
.SH NAME
xz, unxz, xzcat, lzma, unlzma, lzcat \- Compress or decompress .xz and .lzma files
@ -826,14 +826,39 @@ When compressing to the
format, split the input data into blocks of
.I size
bytes.
The blocks are compressed independently from each other.
.\" FIXME: Explain how to these can be used for random access and threading.
The blocks are compressed independently from each other,
which helps with multi-threading and
makes limited random-access decompression possible.
This option is typically used to override the default
block size in multi-threaded mode,
but this option can be used in single-threaded mode too.
.IP ""
In multi-threaded mode the sizes of the blocks
are stored in the block headers.
This isn't done in single-threaded mode,
so the encoded output won't be
identical to that of the multi-threaded mode.
In multi-threaded mode about three times
.I size
bytes will be allocated in each thread for buffering input and output.
The default
.I size
is three times the LZMA2 dictionary size or 1 MiB,
whichever is more.
Typically a good value is 2\-4 times
the size of the LZMA2 dictionary or at least 1 MiB.
Using
.I size
less than the LZMA2 dictionary size is waste of RAM
because then the LZMA2 dictionary buffer will never get fully used.
The sizes of the blocks are stored in the block headers,
which a future version of
.B xz
will use for multi-threaded decompression.
.IP ""
In single-threaded mode no block splitting is done by default.
Setting this option doesn't affect memory usage.
No size information is stored in block headers,
thus files created in single-threaded mode
won't be identical to files created in multi-threaded mode.
The lack of size information also means that a future version of
.B xz
won't be able decompress the files in multi-threaded mode.
.TP
.BI \-\-block\-list= sizes
When compressing to the