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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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<title>Tree Text Locality of Reference Timing Test</title>
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<body>
<div id="page">
<h1>Hash-Based Erase Memory-Use Test</h1>
<h2><a name="description" id="description">Description</a></h2>
<p>This test inserts a number of uniform i.i.d. integer keys
into a container, then erases all keys except one. It measures
the final size of the container.</p>
<p>(The test was executed with <a href="http://gcc.gnu.org/viewcvs/*checkout*/trunk/libstdc%2B%2B-v3/testsuite/performance/ext/pb_ds/hash_random_int_erase_mem_usage.cc"><tt>hash_random_int_erase_mem_usage.cc</tt></a>
2000 2000 2100)</p>
<h2><a name="purpose" id="purpose">Purpose</a></h2>
<p>The test checks how containers adjust internally as their
logical size decreases (see <a href="motivation.html#assoc_ers_methods">Motivation::Associative
Containers::Slightly Different Methods::Methods Related to
Erase</a>).</p>
<h2><a name="results" id="results">Results</a></h2>
<p>Figures <a href="#NHG">NHG</a>, <a href="#NHM">NHM</a> and
<a href="#NHL">NHL</a> show the results for the native and
collision-chaining types in <a href="assoc_performance_tests.html#gcc"><u>g++</u></a>, <a href="assoc_performance_tests.html#msvc"><u>msvc++</u></a> and
<a href="assoc_performance_tests.html#local"><u>local</u></a>,
respectively.</p>
<div id="NHG_res_div">
<div id="NHG_gcc">
<div id="NHG_hash_random_int_erase_mem_usage_test">
<div id="NHG_assoc">
<div id="NHG_Native_456_collision-chaing_456_and_probing_456_hash_random_int_erase_test"><div style="border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NHG" id="NHG"><img src="hash_random_int_erase_mem_usage_test_gcc.png" alt="no image" /></a></h6>NHG: Native, collision-chaing, and probing, hash random int erase test - <a href="assoc_performance_tests.html#gcc">g++</a><p>In the above figure, the names in the legends have the following meaning:</p>
<ol>
<li>
n_hash_set_ncah-
<tt>std::tr1::unordered_set</tt> with <tt>cache_hash_code</tt> = <tt><b>false</b></tt></li>
<li>
gp_hash_mask_linp_exp_nea_lc_1div8_1div2_nsth_set-
<a href="gp_hash_table.html"><tt>gp_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mask_range_hashing.html"><tt>direct_mask_range_hashing</tt></a>
, <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_exponential_size_policy.html"><tt>hash_exponential_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/2</i>, and <tt>Probe_Fn</tt> = <a href="linear_probe_fn.html"><tt>linear_probe_fn</tt></a>
</li>
<li>
cc_hash_mod_prime_nea_lc_1div8_1div1_nsth_set-
<a href="cc_hash_table.html"><tt>cc_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mod_range_hashing.html"><tt>direct_mod_range_hashing</tt></a>
, and <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_prime_size_policy.html"><tt>hash_prime_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/1</i></li>
<li>
cc_hash_mask_exp_nea_lc_1div8_1div2_nsth_set-
<a href="cc_hash_table.html"><tt>cc_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mask_range_hashing.html"><tt>direct_mask_range_hashing</tt></a>
, and <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_exponential_size_policy.html"><tt>hash_exponential_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/2</i></li>
</ol>
</div><div style="width: 100%; height: 20px"></div></div>
</div>
</div>
</div>
</div>
<div id="NHM_res_div">
<div id="NHM_msvc">
<div id="NHM_hash_random_int_erase_mem_usage_test">
<div id="NHM_assoc">
<div id="NHM_Native_456_collision-chaing_456_and_probing_456_hash_random_int_erase_test"><div style="border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NHM" id="NHM"><img src="hash_random_int_erase_mem_usage_test_msvc.png" alt="no image" /></a></h6>NHM: Native, collision-chaing, and probing, hash random int erase test - <a href="assoc_performance_tests.html#msvc">msvc++</a><p>In the above figure, the names in the legends have the following meaning:</p>
<ol>
<li>
n_hash_set_ncah-
<tt>stdext::hash_set</tt></li>
<li>
gp_hash_mask_linp_exp_nea_lc_1div8_1div2_nsth_set-
<a href="gp_hash_table.html"><tt>gp_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mask_range_hashing.html"><tt>direct_mask_range_hashing</tt></a>
, <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_exponential_size_policy.html"><tt>hash_exponential_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/2</i>, and <tt>Probe_Fn</tt> = <a href="linear_probe_fn.html"><tt>linear_probe_fn</tt></a>
</li>
<li>
cc_hash_mod_prime_nea_lc_1div8_1div1_nsth_set-
<a href="cc_hash_table.html"><tt>cc_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mod_range_hashing.html"><tt>direct_mod_range_hashing</tt></a>
, and <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_prime_size_policy.html"><tt>hash_prime_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/1</i></li>
<li>
cc_hash_mask_exp_nea_lc_1div8_1div2_nsth_set-
<a href="cc_hash_table.html"><tt>cc_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mask_range_hashing.html"><tt>direct_mask_range_hashing</tt></a>
, and <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_exponential_size_policy.html"><tt>hash_exponential_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/2</i></li>
</ol>
</div><div style="width: 100%; height: 20px"></div></div>
</div>
</div>
</div>
</div>
<div id="NHM_res_div">
<div id="NHM_msvc">
<div id="NHM_hash_random_int_erase_mem_usage_test">
<div id="NHM_assoc">
<div id="NHM_Native_456_collision-chaing_456_and_probing_456_hash_random_int_erase_test"><div style="border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NHM" id="NHM"><img src="hash_random_int_erase_mem_usage_test_msvc.png" alt="no image" /></a></h6>NHM: Native, collision-chaing, and probing, hash random int erase test - <a href="assoc_performance_tests.html#msvc">msvc++</a><p>In the above figure, the names in the legends have the following meaning:</p>
<ol>
<li>
n_hash_set_ncah-
<tt>stdext::hash_set</tt></li>
<li>
gp_hash_mask_linp_exp_nea_lc_1div8_1div2_nsth_set-
<a href="gp_hash_table.html"><tt>gp_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mask_range_hashing.html"><tt>direct_mask_range_hashing</tt></a>
, <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_exponential_size_policy.html"><tt>hash_exponential_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/2</i>, and <tt>Probe_Fn</tt> = <a href="linear_probe_fn.html"><tt>linear_probe_fn</tt></a>
</li>
<li>
cc_hash_mod_prime_nea_lc_1div8_1div1_nsth_set-
<a href="cc_hash_table.html"><tt>cc_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mod_range_hashing.html"><tt>direct_mod_range_hashing</tt></a>
, and <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_prime_size_policy.html"><tt>hash_prime_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/1</i></li>
<li>
cc_hash_mask_exp_nea_lc_1div8_1div2_nsth_set-
<a href="cc_hash_table.html"><tt>cc_hash_table</tt></a>
with <tt>Comb_Hash_Fn</tt> = <a href="direct_mask_range_hashing.html"><tt>direct_mask_range_hashing</tt></a>
, and <tt>Resize_Policy</tt> = <a href="hash_standard_resize_policy.html"><tt>hash_standard_resize_policy</tt></a>
with <tt>Size_Policy</tt> = <a href="hash_exponential_size_policy.html"><tt>hash_exponential_size_policy</tt></a>
, and <tt>Trigger_Policy</tt> = <a href="hash_load_check_resize_trigger.html"><tt>hash_load_check_resize_trigger</tt></a>
with <i>α<sub>min</sub></i> = <i>1/8</i> and <i>α<sub>max</sub></i> = <i>1/2</i></li>
</ol>
</div><div style="width: 100%; height: 20px"></div></div>
</div>
</div>
</div>
</div>
<div id="NHL_res_div">
<div id="NHL_local">
<div id="NHL_hash_random_int_erase_mem_usage_test">
<div id="NHL_assoc">
<div id="NHL_Native_456_collision-chaing_456_and_probing_456_hash_random_int_erase_test"><div style = "border-style: dotted; border-width: 1px; border-color: lightgray"><h6 class="c1"><a name="NHL" id= "NHL"><img src="hash_random_int_erase_mem_usage_test_local.png" alt="no image" /></a></h6>NHL: Native, collision-chaing, and probing, hash random int erase test - <a href = "assoc_performance_tests.html#local">local</a></div><div style = "width: 100%; height: 20px"></div></div>
</div>
</div>
</div>
</div>
<h2><a name="observations" id="observations">Observations</a></h2>
<p>STL hash-based containers act very differently than trees in
this respect. When erasing numerous keys from an STL
associative-container, the resulting memory user varies greatly
depending on whether the container is tree-based or hash-based.
As noted in <a href="motivation.html#assoc_methods">Motivation::Choice of
Methods</a> , this is a fundamental consequence of the STL's
associative containers' interface, it is not due to a specific
implementation.</p>
<p>(See <a href="priority_queue_text_pop_mem_usage_test.html">Priority Queue
Text <tt>pop</tt> Memory Use Test</a> for a similar phenomenon
regarding priority queues.)</p>
</div>
</body>
</html>
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