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Revise GLEP61 per Calchan questions: Cutoff point moved down to 32KiB, and example size results included; Split specification into generation and validation phases.

1 GLEP: 61
2 Title: Manifest2 compression
3 Version: $Revision: 1.4 $
4 Last-Modified: $Date: 2010/01/13 03:26:53 $
5 Author: Robin Hugh Johnson <robbat2@gentoo.org>
6 Status: Draft
7 Type: Standards Track
8 Content-Type: text/x-rst
9 Requires: 44
10 Created: July 2008
11 Updated: October 2008, January 2010
12 Updates: 44
13 Post-History: December 2009, January 2010
14
15 Abstract
16 ========
17 Deals with compression of large Manifest2 files.
18
19 Motivation
20 ==========
21 With the introduction of MetaManifest, and full-tree Manifest coverage,
22 we are faced with the possibility of having very large Manifests.
23
24 Preliminary experiments with MetaManifest, show that with just the
25 existing per-package Manifests, the full MetaManifest (top-level only,
26 no first-level sub directories), for a tree including metadata/, exceeds
27 8MiB in size. Applying common compression can achieve a 50-60% reduction
28 in this size.
29
30 Additionally, some of the larger already-existing Manifests in the tree
31 can also be reduced.
32
33 Specification
34 =============
35 Creation of compressed Manifests:
36 ---------------------------------
37 32KiB is suggested as a arbitrary cut-off point to start generating
38 compressed Manifest2 files.
39
40 The compression must only applied during the creation of a tree intended
41 for end users. No Manifests stored in a VCS should be compressed in the
42 VCS. For the main gentoo-portage tree, this means that the compressed
43 Manifests should be generated using the CVS to Rsync process.
44
45 The Manifest compression process is required to ensure that inconsistent
46 compressed versions do not exist.
47
48 Validation of Manifests:
49 ------------------------
50 When searching for a Manifest2 file, if the basename form does not
51 exist, the package manager should search in the same location using
52 common compressed suffixes, and use the compressed file in place of the
53 Manifest2.
54
55 gzip, bzip2, lzma, xz should all be supported if available on the given
56 platform. In the case that multiple versions exist, the package manager
57 should simply pick one - they should be identical, differing only in
58 compression.
59
60 Example Results with a 32KiB cut-off, gzip algorithm
61 ====================================================
62 As of 2010/01/30, the suggested cut-off would impact the following 21 existing
63 Manifests, for a saving of nearly 900KiB::
64
65 Size Path
66 65788 app-doc/linux-gazette/Manifest
67 75739 app-office/openoffice-bin/Manifest
68 40534 app-text/texlive-core/Manifest
69 41710 dev-texlive/texlive-bibtexextra/Manifest
70 38197 dev-texlive/texlive-documentation-english/Manifest
71 129610 dev-texlive/texlive-fontsextra/Manifest
72 36022 dev-texlive/texlive-humanities/Manifest
73 686118 dev-texlive/texlive-latexextra/Manifest
74 43392 dev-texlive/texlive-latexrecommended/Manifest
75 33375 dev-texlive/texlive-mathextra/Manifest
76 39781 dev-texlive/texlive-pictures/Manifest
77 69567 dev-texlive/texlive-pstricks/Manifest
78 75460 dev-texlive/texlive-publishers/Manifest
79 50879 dev-texlive/texlive-science/Manifest
80 36711 kde-base/kde-l10n/Manifest
81 36539 media-gfx/bootsplash-themes/Manifest
82 33058 net-fs/autofs/Manifest
83 39781 www-client/firefox-bin/Manifest
84 48983 www-client/icecat/Manifest
85 60213 www-client/mozilla-firefox/Manifest
86 39065 x11-themes/gkrellm-themes/Manifest
87
88
89 Additionally, with the MetaManifest proposal, the following new manifests would
90 also be compressed, for a saving of nearly 4MiB::
91
92 Size Path
93 33442 app-admin/Manifest
94 71073 app-dicts/Manifest
95 35923 app-emacs/Manifest
96 45808 app-misc/Manifest
97 50169 app-text/Manifest
98 112786 dev-java/Manifest
99 65581 dev-libs/Manifest
100 42619 dev-lisp/Manifest
101 182163 dev-perl/Manifest
102 96198 dev-python/Manifest
103 58963 dev-ruby/Manifest
104 59736 dev-util/Manifest
105 58338 eclass/Manifest
106 55749 kde-base/Manifest
107 110064 licenses/Manifest
108 35262 media-gfx/Manifest
109 53995 media-libs/Manifest
110 55607 media-plugins/Manifest
111 71911 media-sound/Manifest
112 34835 media-video/Manifest
113 5747849 metadata/Manifest
114 47452 net-analyzer/Manifest
115 65989 net-misc/Manifest
116 316787 profiles/Manifest
117 67784 sys-apps/Manifest
118 48971 x11-misc/Manifest
119 41475 x11-plugins/Manifest
120
121
122 Backwards Compatibility
123 =======================
124 The package Manifests should also be maintained as ONLY uncompressed in
125 CVS.
126
127 For processing of all existing per-package Manifests, if compression is
128 used, it should be done in parallel to the existing Manifests, to
129 provide for a changeover period. Newer versions of Portage may later
130 choose to exclude all non-compressed Manifests during emerge --sync if
131 compressed versions are guaranteed to exist on the servers.
132
133 MetaManifests may come into existence as compressed from the start, as
134 do not have an backwards compatibility issues.
135
136 As a side note, this breaks all manual interaction with Manifests
137 such as grep, and so should only be applied to large Manifest2 files,
138 such as the MetaManifest.
139
140 References
141 ==========
142 .. [#GLEP44] Mauch, M. (2005) GLEP44 - Manifest2 format.
143 http://www.gentoo.org/proj/en/glep/glep-0044.html
144
145 Copyright
146 =========
147 Copyright (c) 2008-2010 by Robin Hugh Johnson. This material may be
148 distributed only subject to the terms and conditions set forth in the
149 Open Publication License, v1.0.
150
151 vim: tw=72 ts=2 expandtab:

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