PERF: restore kh_get before kh_put in hashtable operations#65026
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jbrockmendel wants to merge 1 commit intopandas-dev:mainfrom
Open
PERF: restore kh_get before kh_put in hashtable operations#65026jbrockmendel wants to merge 1 commit intopandas-dev:mainfrom
jbrockmendel wants to merge 1 commit intopandas-dev:mainfrom
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Partially reverts pandas-dev#64543, which replaced kh_get + kh_put with kh_put alone. While kh_put avoids a redundant hash for new keys, it is more expensive than kh_get for existing keys due to extra branching (resize checks, deleted-slot tracking). For low-cardinality data (e.g. boolean with 2 unique values), nearly all lookups hit existing keys, causing ~80% regression at the Cython level. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
kh_get+kh_putwithkh_putalone in the hashtable_unique,get_labels_groupby,value_count, andduplicatedmethodskh_putavoids a redundant hash for new keys, it is more expensive thankh_getfor existing keys due to extra branching in khash (resize checks, deleted-slot tracking)Factorize.time_factorizeat the Cython levelTest plan
test_algos.pyandtest_hashtable.pytests passalgorithms.Factorize.time_factorizefor boolean dtype matches v3.0 performance🤖 Generated with Claude Code