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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
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>
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>
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>,
41 <div id="NTG_res_div">
43 <div id="NTG_tree_split_join_timing_test">
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>
49 <tt>std::set</tt></li>
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>
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>
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>
69 </div><div style="width: 100%; height: 20px"></div></div>
74 <div id="NTM_res_div">
76 <div id="NTM_tree_split_join_timing_test">
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>
82 <tt>std::set</tt></li>
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>
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>
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>
102 </div><div style="width: 100%; height: 20px"></div></div>
107 <div id="NTL_res_div">
109 <div id="NTL_tree_split_join_timing_test">
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>
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>