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7<title>Tree Split Join Timing Test</title>
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12<h1>Tree Split-Join Timing Test</h1>
13<h2><a name="description" id="description">Description</a></h2>
14<p>This test a container, inserts into a number of values,
15    splits the container at the median, and joins the two
16    containers. (If the containers are one of <tt>pb_ds</tt> 's
17    trees, it splits and joins with the <tt>split</tt> and
18    <tt>join</tt> method; otherwise, it uses the <tt>erase</tt> and
19    <tt>insert</tt> methods.) It measures the time for splitting
20    and joining the containers as a function of the number of
21    values inserted.</p>
22<p>(The test was executed with <a href="http://gcc.gnu.org/viewcvs/*checkout*/trunk/libstdc%2B%2B-v3/testsuite/performance/ext/pb_ds/tree_split_join_timing.cc"><tt>tree_split_join_timing_test</tt></a>
23    200 200 2100)</p>
24<h2><a name="purpose" id="purpose">Purpose</a></h2>
25<p>The test checks the performance difference of <tt>join</tt>
26    as opposed to a sequence of <tt>insert</tt> operations; by
27    implication, this test checks the most efficient way to erase a
28    sub-sequence from a tree-like-based container, since this can
29    always be performed by a small sequence of splits and joins
30    (see <a href="motivation.html#assoc_split_join_methods">Motivation::Associative
31    Containers::Slightly Different Methods::Methods Related to
32    Split and Join</a> and <a href="tree_based_containers.html#add_methods">Design::Associative
33    Containers::Tree-Based Containers::Additional Methods</a>
34    .)</p>
35<h2><a name="results" id="results">Results</a></h2>
36<p>Figures <a href="#NTG">NTG</a>, <a href="#NTM">NTM</a>, and
37    <a href="#NTL">NTL</a> show the results for the native and
38    tree-based containers in <a href="assoc_performance_tests.html#gcc"><u>g++</u></a>, <a href="assoc_performance_tests.html#msvc"><u>msvc++</u></a>, and
39    <a href="assoc_performance_tests.html#local"><u>local</u></a>,
40    respectively.</p>
41<div id="NTG_res_div">
42<div id="NTG_gcc">
43<div id="NTG_tree_split_join_timing_test">
44<div id="NTG_assoc">
45<div id="NTG_Native_and_tree-based_container_splits_and_joins"><div style="border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NTG" id="NTG"><img src="tree_split_join_timing_test_gcc.png" alt="no image" /></a></h6>NTG: Native and tree-based container splits and joins - <a href="assoc_performance_tests.html#gcc">g++</a><p>In the above figure, the names in the legends have the following meaning:</p>
46<ol>
47<li>
48n_set-
49<tt>std::set</tt></li>
50<li>
51splay_tree_set-
52<a href="tree.html"><tt>tree</tt></a>
53 with <tt>Tag</tt> = <a href="splay_tree_tag.html"><tt>splay_tree_tag</tt></a>
54, and <tt>Node_Update</tt> = <a href="null_tree_node_update.html"><tt>null_tree_node_update</tt></a>
55</li>
56<li>
57rb_tree_set-
58<a href="tree.html"><tt>tree</tt></a>
59 with <tt>Tag</tt> = <a href="rb_tree_tag.html"><tt>rb_tree_tag</tt></a>
60, and <tt>Node_Update</tt> = <a href="null_tree_node_update.html"><tt>null_tree_node_update</tt></a>
61</li>
62<li>
63ov_tree_set-
64<a href="tree.html"><tt>tree</tt></a>
65 with <tt>Tag</tt> = <a href="ov_tree_tag.html"><tt>ov_tree_tag</tt></a>
66, and <tt>Node_Update</tt> = <a href="null_tree_node_update.html"><tt>null_tree_node_update</tt></a>
67</li>
68</ol>
69</div><div style="width: 100%; height: 20px"></div></div>
70</div>
71</div>
72</div>
73</div>
74<div id="NTM_res_div">
75<div id="NTM_msvc">
76<div id="NTM_tree_split_join_timing_test">
77<div id="NTM_assoc">
78<div id="NTM_Native_and_tree-based_container_splits_and_joins"><div style="border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NTM" id="NTM"><img src="tree_split_join_timing_test_msvc.png" alt="no image" /></a></h6>NTM: Native and tree-based container splits and joins - <a href="assoc_performance_tests.html#msvc">msvc++</a><p>In the above figure, the names in the legends have the following meaning:</p>
79<ol>
80<li>
81n_set-
82<tt>std::set</tt></li>
83<li>
84splay_tree_set-
85<a href="tree.html"><tt>tree</tt></a>
86 with <tt>Tag</tt> = <a href="splay_tree_tag.html"><tt>splay_tree_tag</tt></a>
87, and <tt>Node_Update</tt> = <a href="null_tree_node_update.html"><tt>null_tree_node_update</tt></a>
88</li>
89<li>
90rb_tree_set-
91<a href="tree.html"><tt>tree</tt></a>
92 with <tt>Tag</tt> = <a href="rb_tree_tag.html"><tt>rb_tree_tag</tt></a>
93, and <tt>Node_Update</tt> = <a href="null_tree_node_update.html"><tt>null_tree_node_update</tt></a>
94</li>
95<li>
96ov_tree_set-
97<a href="tree.html"><tt>tree</tt></a>
98 with <tt>Tag</tt> = <a href="ov_tree_tag.html"><tt>ov_tree_tag</tt></a>
99, and <tt>Node_Update</tt> = <a href="null_tree_node_update.html"><tt>null_tree_node_update</tt></a>
100</li>
101</ol>
102</div><div style="width: 100%; height: 20px"></div></div>
103</div>
104</div>
105</div>
106</div>
107<div id="NTL_res_div">
108<div id="NTL_local">
109<div id="NTL_tree_split_join_timing_test">
110<div id="NTL_assoc">
111<div id="NTL_Native_and_tree-based_container_splits_and_joins"><div style = "border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NTL" id= "NTL"><img src="tree_split_join_timing_test_local.png" alt="no image" /></a></h6>NTL: Native and tree-based container splits and joins - <a href = "assoc_performance_tests.html#local">local</a></div><div style = "width: 100%; height: 20px"></div></div>
112</div>
113</div>
114</div>
115</div>
116<h2><a name="observations" id="observations">Observations</a></h2>
117<p>In this test, the native red-black trees must be split and
118    joined externally, through a sequence of <tt>erase</tt> and
119    <tt>insert</tt> operations. This is clearly super-linear, and
120    it is not that surprising that the cost is high.</p>
121<p><tt>pb_ds</tt> 's tree-based containers use in this test the
122    <tt>split</tt> and <tt>join</tt> methods, which have lower
123    complexity: the <tt>join</tt> method of a splay tree ( <a href="tree.html"><tt>tree</tt></a>
124    with <tt>Tag =</tt> <a href="splay_tree_tag.html"><tt>splay_tree_tag</tt></a> ) is
125    quadratic in the length of the longest root-leaf path, and
126    linear in the total number of elements; the <tt>join</tt>
127    method of a red-black tree ( <a href="tree.html"><tt>tree</tt></a>
128    with <tt>Tag =</tt> <a href="rb_tree_tag.html"><tt>rb_tree_tag</tt></a> ) or an
129    ordered-vector tree ( <a href="tree.html"><tt>tree</tt></a>
130    with <tt>Tag =</tt> <a href="ov_tree_tag.html"><tt>ov_tree_tag</tt></a> ) is linear
131    in the number of elements.</p>
132<p>Asides from orders of growth, <tt>pb_ds</tt> 's trees access
133    their allocator very little in these operations, and some of
134    them do not access it at all. This leads to lower constants in
135    their complexity, and, for some containers, to exception-free
136    splits and joins (which can be determined via <a href="assoc_container_traits.html"><tt>container_traits</tt></a>).</p>
137<p>It is important to note that <tt>split</tt> and
138    <tt>join</tt> are not esoteric methods - they are the most
139    efficient means of erasing a contiguous range of values from a
140    tree based container.</p>
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