1nbdkit-xz-filter(1)                 NBDKIT                 nbdkit-xz-filter(1)
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NAME

6       nbdkit-xz-filter - nbdkit xz filter
7

SYNOPSIS

9        nbdkit --filter=xz file FILENAME.xz
10
11        nbdkit --filter=xz curl https://example.com/FILENAME.xz
12

DESCRIPTION

14       "nbdkit-xz-filter" is a filter for nbdkit(1) which uncompresses the
15       underlying plugin on the fly.  The filter only supports read-only
16       connections.
17
18   Getting best random access performance from xz
19       xz(1) files are split into streams and blocks.  Most xz files contain
20       only one stream which contains one or more blocks.  You can find out
21       how many streams and blocks are in an xz file by doing:
22
23        $ xz --list winxp.img.xz
24        Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
25            1       1  2,100.0 MiB  6,144.0 MiB  0.342  CRC64   winxp.img.xz
26           ↑↑↑     ↑↑↑
27         streams  blocks
28
29       xz files are seekable on block boundaries only.  Seeking is done by
30       seeking directly to the lower block boundary, then uncompressing data
31       until the precise byte is reached.  As uncompressing xz data is slow,
32       to get best random access performance, you must prepare your xz files
33       with many small blocks.
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35       Use the --block-size option with a small-ish block size.  For example
36       this is the same image compressed with a 16 MB block size:
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38        $ xz --best --block-size=16777216 winxp.img
39                    ─────────────────────
40        $ xz --list winxp.img.xz
41        Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
42            1     384  2,120.1 MiB  6,144.0 MiB  0.345  CRC64   winxp.img.xz
43                  ↑↑↑
44                 blocks
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46       This file can be accessed randomly.  At most 16 MB will have to be
47       uncompressed to seek to any byte.
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49       As you would expect, xz cannot compress as efficiently when using a
50       smaller block size.  The space penalty in the above example is < 1% of
51       the compressed file size.
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PARAMETERS

54       xz-max-block=SIZE
55           The maximum block size that the filter will read.  The filter will
56           refuse to read xz files that contain any block larger than this
57           size.
58
59           See the discussion above about creating xz files with small block
60           sizes in order to reduce memory usage and increase performance.
61
62           This parameter is optional.  If not specified it defaults to 512M.
63
64       xz-max-depth=N
65           Maximum number of blocks stored in the LRU block cache.
66
67           This parameter is optional.  If not specified it defaults to 8.
68
69           The filter may allocate up to maximum block size in file * maxdepth
70           bytes of memory per connection.
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FILES

73       $filterdir/nbdkit-xz-filter.so
74           The filter.
75
76           Use "nbdkit --dump-config" to find the location of $filterdir.
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VERSION

79       "nbdkit-xz-filter" first appeared in nbdkit 1.10.
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SEE ALSO

82       nbdkit(1), nbdkit-filter(3), nbdkit-curl-plugin(1),
83       nbdkit-file-plugin(1), xz(1).
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AUTHORS

86       Richard W.M. Jones
87

89       Copyright (C) 2013-2018 Red Hat Inc.
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LICENSE

92       Redistribution and use in source and binary forms, with or without
93       modification, are permitted provided that the following conditions are
94       met:
95
96       ·   Redistributions of source code must retain the above copyright
97           notice, this list of conditions and the following disclaimer.
98
99       ·   Redistributions in binary form must reproduce the above copyright
100           notice, this list of conditions and the following disclaimer in the
101           documentation and/or other materials provided with the
102           distribution.
103
104       ·   Neither the name of Red Hat nor the names of its contributors may
105           be used to endorse or promote products derived from this software
106           without specific prior written permission.
107
108       THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
109       EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
110       IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
111       PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
112       LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
113       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
114       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
115       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
116       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
117       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
118       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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122nbdkit-1.16.1                     2019-12-03               nbdkit-xz-filter(1)
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