Line data Source code
1 : // Copyright (c) 2019 Made to Order Software Corp. All Rights Reserved
2 : //
3 : // https://snapwebsites.org/project/snapdatabase
4 : // contact@m2osw.com
5 : //
6 : // This program is free software; you can redistribute it and/or modify
7 : // it under the terms of the GNU General Public License as published by
8 : // the Free Software Foundation; either version 2 of the License, or
9 : // (at your option) any later version.
10 : //
11 : // This program is distributed in the hope that it will be useful,
12 : // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 : // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 : // GNU General Public License for more details.
15 : //
16 : // You should have received a copy of the GNU General Public License along
17 : // with this program; if not, write to the Free Software Foundation, Inc.,
18 : // 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
19 : #pragma once
20 :
21 :
22 : /** \file
23 : * \brief Block representing the database file header.
24 : *
25 : */
26 :
27 : // self
28 : //
29 : #include "snapdatabase/data/structure.h"
30 :
31 :
32 :
33 :
34 :
35 : namespace snapdatabase
36 : {
37 :
38 :
39 :
40 : /** \brief The type of Bloom Filter.
41 : *
42 : * We want to support multiple implementations to help with the ignorance
43 : * of what is best.
44 : *
45 : * * None
46 : *
47 : * Means that no Bloom Filter is used (good for _tiny_ tables).
48 : *
49 : * * One
50 : *
51 : * Means that we use a single buffer for all the hashes. That means
52 : * we may have some overlap (although this is how it usually is
53 : * implemented).
54 : *
55 : * * N
56 : *
57 : * Means we use one buffer per hash. No overlap, but instead of
58 : * a one time 250Kb buffer, we need something like N x 250Kb
59 : * (where N is the number of hashes).
60 : *
61 : * Keep in mind that N is generally pretty large (i.e. 7 to 23).
62 : * So it's not cheap.
63 : *
64 : * * Bits
65 : *
66 : * Means that the filter is just bits: 0 no luck, 1 row exists.
67 : *
68 : * As a result, this Bloom Filters are not good with tables where
69 : * many deletion occur because ultimately you get so many false
70 : * positives that the filter could just be ignored. To fix the
71 : * problem you have to regenerate the Bloom Filter from scratch.
72 : *
73 : * * Counters
74 : *
75 : * Means that we use 8 bits and count how many rows make use
76 : * of that bit. That way we can decrement the counter later when
77 : * the row gets deleted. So this is best for tables that have many
78 : * deletes.
79 : *
80 : * Note that if the counter reaches the maximum (255 for us since we
81 : * plane to use 8 bits for each counter), you have a similar problem
82 : * as with the Bits version above. You have to reference the
83 : * entire filter with a large Bloom Filter.
84 : */
85 : enum class bloom_filter_algorithm_t : uint8_t
86 : {
87 : BLOOM_FILTER_ALGORITHM_NONE = 0,
88 : BLOOM_FILTER_ALGORITHM_ONE_BITS = 1,
89 : BLOOM_FILTER_ALGORITHM_ONE_COUNTERS = 2,
90 : BLOOM_FILTER_ALGORITHM_N_BITS = 3,
91 : BLOOM_FILTER_ALGORITHM_N_COUNTERS = 4,
92 : };
93 :
94 :
95 :
96 0 : class file_snap_database_table
97 : : public block
98 : {
99 : public:
100 : typedef std::shared_ptr<file_snap_database_table> pointer_t;
101 :
102 : file_snap_database_table(dbfile::pointer_t f, reference_t offset);
103 :
104 : version_t get_file_version() const;
105 : void set_file_version(version_t v);
106 : reference_t get_first_free_block() const;
107 : void set_first_free_block(reference_t offset);
108 : reference_t get_table_definition() const;
109 : void set_table_definition(reference_t offset);
110 : uint32_t get_block_size() const;
111 : void set_block_size(uint32_t size);
112 :
113 : private:
114 : //schema_table::pointer_t f_schema = schema_table::pointer_t();
115 : };
116 :
117 :
118 :
119 : } // namespace snapdatabase
120 : // vim: ts=4 sw=4 et
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