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MDEV-35049: Avoid building AHI beyond unique field prefix

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During a workload, an adaptive hash index had been built on
UNIQUE INDEX(ID) on SYS_TABLES, and during a DROP TABLE
operation the adaptive hash index would be widened to cover
also the PRIMARY KEY(NAME) field that the index includes: (ID,NAME).
Such an adaptive hash index is unlikely to satisfy (m)any queries.
Let us limit the AHI prefix to the unique fields.

Reviewed by: Vladislav Lesin
This commit is contained in:
Marko Mäkelä 2025-01-10 16:40:35 +02:00
parent 5f7b2a3ced
commit 4221ed1d7d
1 changed files with 4 additions and 5 deletions
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9
storage/innobase/btr/btr0sea.cc
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@ -523,7 +523,8 @@ static uint32_t btr_search_info_update_hash(const btr_cur_t &cursor) noexcept
const dict_index_t *const block_index= block->index;
uint16_t n_hash_helps{block->n_hash_helps};
const uint16_t n_uniq{dict_index_get_n_unique_in_tree(index)};
const uint16_t n_uniq=
uint16_t(index->n_uniq ? index->n_uniq : index->n_fields);
dict_index_t::ahi &info= index->search_info;
uint32_t left_bytes_fields{info.left_bytes_fields};
uint8_t n_hash_potential= info.n_hash_potential;
@ -1472,10 +1473,8 @@ static void btr_search_build_page_hash_index(dict_index_t *index,
/* Check that the values for hash index build are sensible */
ut_ad(n_bytes_fields);
if (dict_index_get_n_unique_in_tree(index) <
btr_search_get_n_fields(n_bytes_fields))
return;
ut_ad(btr_search_get_n_fields(n_bytes_fields) <=
(index->n_uniq ? index->n_uniq : index->n_fields));
const page_t *const page= block->page.frame;
size_t n_cached= 0;