Hash-Based Random-Integer operator[] Insert
Timing Test
This test inserts a number of values with uniform i.i.d.
integer keys into a container, using
operator[]. It measures the average time for
operator[] as a function of the number of
values inserted.
(The test was executed with hash_random_int_subscript_insert_timing_test
200 200 2100)
The test primarily checks the effect of different underlying
hash-tables (see Design::Associative
Containers::Associative Containers::Hash-Based
Containers).
Figures NCCG, NCCM,
and NCCL show the results for the native
and collision-chaining types in g++, MSVC++, and
local,
respectively; Figures NGPG, NGPM, and NGPL show the results
for the native and probing types in g++, msvc++, and
local
respectively; Figures CCGPG, CCGPM, and CCGPL compare the
results for the collision-chaining and probing types of
pb_ds only, in g++, MSVC++, and
local
respectively.
NCCL: Native and collision-chaining hash random int insert timing test using
operator -
local
NGPL: Native and probing hash random int insert timing test using
operator -
local
CCGPG: Collision-chaining and probing hash random int insert timing test using
operator -
g++In the above figure, the names in the legends have the following meaning:
-
gp_hash_mod_quadp_prime_nea_lc_1div8_1div2_nsth_map-
gp_hash_table
with Comb_Hash_Fn = direct_mod_range_hashing
, Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_prime_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2, and Probe_Fn = quadratic_probe_fn
-
cc_hash_mod_prime_nea_lc_1div8_1div2_nsth_map-
cc_hash_table
with Comb_Hash_Fn = direct_mod_range_hashing
, and Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_prime_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2
-
cc_hash_mask_exp_nea_lc_1div8_1div2_nsth_map-
cc_hash_table
with Comb_Hash_Fn = direct_mask_range_hashing
, and Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_exponential_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2
-
gp_hash_mask_linp_exp_nea_lc_1div8_1div2_nsth_map-
gp_hash_table
with Comb_Hash_Fn = direct_mask_range_hashing
, Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_exponential_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2, and Probe_Fn = linear_probe_fn
CCGPM: Collision-chaining and probing hash random int insert timing test using
operator -
msvc++In the above figure, the names in the legends have the following meaning:
-
cc_hash_mod_prime_nea_lc_1div8_1div2_nsth_map-
cc_hash_table
with Comb_Hash_Fn = direct_mod_range_hashing
, and Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_prime_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2
-
cc_hash_mask_exp_nea_lc_1div8_1div2_nsth_map-
cc_hash_table
with Comb_Hash_Fn = direct_mask_range_hashing
, and Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_exponential_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2
-
gp_hash_mod_quadp_prime_nea_lc_1div8_1div2_nsth_map-
gp_hash_table
with Comb_Hash_Fn = direct_mod_range_hashing
, Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_prime_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2, and Probe_Fn = quadratic_probe_fn
-
gp_hash_mask_linp_exp_nea_lc_1div8_1div2_nsth_map-
gp_hash_table
with Comb_Hash_Fn = direct_mask_range_hashing
, Resize_Policy = hash_standard_resize_policy
with Size_Policy = hash_exponential_size_policy
, and Trigger_Policy = hash_load_check_resize_trigger
with αmin = 1/8 and αmax = 1/2, and Probe_Fn = linear_probe_fn
CCGPL: Collision-chaining and probing hash random int insert timing test using
operator -
local
In this setting, as in Hash-Based Text
find Find Timing Test and Hash-Based
Random-Integer find Find Timing Test , the choice
of underlying hash-table underlying hash-table (see Design::Associative
Containers::Hash-Based Containers ) affects performance
most, then the range-hashing scheme (See Design::Associative
Containers::Hash-Based Containers::Hash Policies ), and,
only finally, other policies.
There are some differences, however:
- In this setting, probing tables function sometimes more
efficiently than collision-chaining tables (see Figures
CCGPG and CCGPM ).
This is explained shortly.
- The performance graphs have a "saw-tooth" shape. The
average insert time rises and falls. As values are inserted
into the container, the load factor grows larger. Eventually,
a resize occurs. The reallocations and rehashing are
relatively expensive. After this, the load factor is smaller
than before.
Collision-chaining containers use indirection for greater
flexibility; probing containers store values contiguously, in
an array (see Figure Motivation::Different
underlying data structures A and B, respectively). It
follows that for simple data types, probing containers access
their allocator less frequently than collision-chaining
containers, (although they still have less efficient probing
sequences). This explains why some probing containers fare
better than collision-chaining containers in this case.
Within each type of hash-table, the range-hashing scheme
affects performance more than other policies. This is similar
to the situation in Hash-Based Text
find Find Timing Test and Hash-Based
Random-Integer find Find Timing Test.
Unsurprisingly, however, containers with lower
alphamax perform worse in this case,
since more re-hashes are performed.
Observations::Hash-Based
Container Types summarizes some observations on hash-based
containers; Observations::Hash-Based
Containers' Policies summarizes some observations on
hash-based containers' policies.