Replace pair_list with hash table

[asvetlov]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging #1128 will degrade performances by 28.85%

_{Comparing ht (cab2a3e) with master (99e3f3b)}

Summary

⚡ 66 improvements
❌ 11 regressions
✅ 167 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	test_cimultidict_add_istr[c-extension-module]	2.7 ms	3.5 ms	-23.57%
⚡	test_cimultidict_delitem_istr[c-extension-module]	86 µs	63.2 µs	+36.17%
❌	test_cimultidict_extend_istr[c-extension-module]	2.4 ms	2.9 ms	-15.89%
❌	test_cimultidict_extend_istr_with_kwargs[c-extension-module]	6.5 ms	7.6 ms	-14.48%
⚡	test_cimultidict_fetch_istr[c-extension-module]	57.9 µs	45.3 µs	+27.98%
⚡	test_cimultidict_get_istr_hit[c-extension-module]	69.5 µs	56.9 µs	+22.08%
⚡	test_cimultidict_get_istr_hit_with_default[c-extension-module]	71.4 µs	58.8 µs	+21.3%
⚡	test_cimultidict_get_istr_miss[c-extension-module]	73.1 µs	46.3 µs	+57.86%
⚡	test_cimultidict_get_istr_with_default_miss[c-extension-module]	75.1 µs	48.4 µs	+55.29%
⚡	test_cimultidict_getall_istr_miss[c-extension-module]	16.3 µs	14.7 µs	+10.81%
⚡	test_cimultidict_insert_istr[c-extension-module]	66.3 µs	48.2 µs	+37.64%
⚡	test_cimultidict_pop_istr[c-extension-module]	83.5 µs	73.4 µs	+13.75%
⚡	test_cimultidict_update_istr[c-extension-module]	126.8 µs	45.1 µs	×2.8
⚡	test_cimultidict_update_istr_with_kwargs[c-extension-module]	294.9 µs	149.9 µs	+96.8%
⚡	test_copy_from_existing_cimultidict[c-extension-module]	18.9 µs	17.3 µs	+9.06%
❌	test_create_cimultidict_with_dict_istr[c-extension-module]	40.5 µs	44.9 µs	-9.75%
⚡	test_create_cimultidict_with_items_istr[c-extension-module]	52.2 µs	46 µs	+13.52%
⚡	test_create_multidict_with_items[case-sensitive-c-extension-module]	48.3 µs	41.3 µs	+16.75%
❌	test_multidict_add_str[case-insensitive-c-extension-module]	5.5 ms	6.4 ms	-13.72%
❌	test_multidict_add_str[case-sensitive-c-extension-module]	2 ms	2.8 ms	-28.85%
...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

[asvetlov]

Heh. Appending new values to the multidict is more expensive, all other ops are faster.

We have a tradeoff, as usual. I think that the lookup is a much more often operation than the multidict filling.
Also, pls keep in mind that the item replacement/deletion also requires a lookup.