MDEV-35049: Fix bogus BTR_CUR_HASH_FAIL on contention

btr_search_guess_on_hash(): Only set BTR_CUR_HASH_FAIL on actual mismatch.
If the page latch cannot be acquired, the hash search might very well
have succeeded. Do not count that as a failure, that is, do not
unnecessarily invoke btr_search_update_hash_ref() after a normal search.
Set cursor->flag=BTR_CUR_HASH_ABORT if the current parameters of the
adaptive hash index are not suitable for the search and a call to
btr_cur_t::search_info_update() might help.

btr_cur_t::search_leaf(): Do not invoke search_info_update()
if btr_search_guess_on_hash() failed due to contention.

btr_cur_t::pessimistic_search_leaf(): Do not invoke search_info_update()
on the change buffer tree. Preivously, this condition was being checked
inside search_info_update().

Author: dr-m

storage/innobase/btr/btr0cur.cc

@@ -1423,18 +1423,14 @@ dberr_t btr_cur_t::search_leaf(const dtuple_t *tuple, page_cur_mode_t mode,
         goto need_opposite_intention;
 
 #ifdef BTR_CUR_HASH_ADAPT
-    /* We do a dirty read of btr_search.enabled here.  We will recheck in
-    btr_search_build_page_hash_index() before building a page hash
-    index, while holding search latch. */
-    if (!btr_search.enabled);
-    else if (tuple->info_bits & REC_INFO_MIN_REC_FLAG)
-      /* This may be a search tuple for btr_pcur_t::restore_position(). */
-      ut_ad(tuple->is_metadata() ||
-            (tuple->is_metadata(tuple->info_bits ^ REC_STATUS_INSTANT)));
-    else if (index()->table->is_temporary());
-    else if (!rec_is_metadata(page_cur.rec, *index()) &&
-             index()->search_info.hash_analysis_useful())
-      search_info_update();
+    if (flag != BTR_CUR_BINARY)
+    {
+      ut_ad(!(tuple->info_bits & REC_INFO_MIN_REC_FLAG));
+      ut_ad(!index()->table->is_temporary());
+      if (!rec_is_metadata(page_cur.rec, *index()) &&
+          index()->search_info.hash_analysis_useful())
+        search_info_update();
+    }
 #endif /* BTR_CUR_HASH_ADAPT */
 
     goto func_exit;

storage/innobase/btr/btr0sea.cc

@@ -501,10 +501,11 @@ static void btr_search_update_hash_ref(const btr_cur_t &cursor,
 @retval 0 if the adaptive hash index should not be rebuilt */
 static uint32_t btr_search_info_update_hash(const btr_cur_t &cursor) noexcept
 {
-  ut_ad(cursor.flag != BTR_CUR_HASH);
+  ut_ad(cursor.flag == BTR_CUR_HASH_FAIL ||
+        cursor.flag == BTR_CUR_HASH_ABORT ||
+        cursor.flag == BTR_CUR_BINARY);
 
   dict_index_t *const index= cursor.index();
-
   const uint16_t n_uniq{dict_index_get_n_unique_in_tree(index)};
   dict_index_t::ahi &info= index->search_info;
 
@@ -1046,11 +1047,19 @@ btr_search_guess_on_hash(
   ut_ad(mtr->is_active());
   ut_ad(index->is_btree());
   ut_ad(latch_mode == BTR_SEARCH_LEAF || latch_mode == BTR_MODIFY_LEAF);
+  ut_ad(cursor->flag == BTR_CUR_BINARY);
+
+  if ((tuple->info_bits & REC_INFO_MIN_REC_FLAG))
+    return false;
 
-  if ((tuple->info_bits & REC_INFO_MIN_REC_FLAG) ||
-      !index->search_info.last_hash_succ ||
+  if (!index->search_info.last_hash_succ ||
       !index->search_info.n_hash_potential)
+  {
+  ahi_unusable:
+    if (!index->table->is_temporary() && btr_search.enabled)
+      cursor->flag= BTR_CUR_HASH_ABORT;
     return false;
+  }
 
   ut_ad(!index->table->is_temporary());
 
@@ -1061,7 +1070,7 @@ btr_search_guess_on_hash(
     ~buf_block_t::LEFT_SIDE;
 
   if (dtuple_get_n_fields(tuple) < btr_search_get_n_fields(cursor))
-    return false;
+    goto ahi_unusable;
 
   const index_id_t index_id= index->id;
 
@@ -1070,7 +1079,6 @@ btr_search_guess_on_hash(
 #endif
   const uint32_t fold= dtuple_fold(tuple, cursor);
   cursor->fold= fold;
-  cursor->flag= BTR_CUR_HASH;
   btr_sea::partition &part= btr_search.get_part(*index);
 
   part.latch.rd_lock(SRW_LOCK_CALL);
@@ -1080,8 +1088,6 @@ btr_search_guess_on_hash(
   ahi_release_and_fail:
     part.latch.rd_unlock();
   fail:
-    cursor->flag= BTR_CUR_HASH_FAIL;
-
 #ifdef UNIV_SEARCH_PERF_STAT
     ++index->search_info.n_hash_fail;
     if (index->search_info.n_hash_succ > 0)
@@ -1096,7 +1102,10 @@ btr_search_guess_on_hash(
     { return node->fold == fold; });
 
   if (!node)
+  {
+    cursor->flag= BTR_CUR_HASH_FAIL;
     goto ahi_release_and_fail;
+  }
 
   const rec_t *rec= node->rec;
   buf_block_t *block= buf_pool.block_from_ahi(rec);
@@ -1127,6 +1136,7 @@ btr_search_guess_on_hash(
       block->page.lock.s_unlock();
     else
       block->page.lock.x_unlock();
+    cursor->flag= BTR_CUR_HASH_FAIL;
     goto ahi_release_and_fail;
   }
 
@@ -1137,6 +1147,7 @@ btr_search_guess_on_hash(
   if (index != block_index && index_id == block_index->id)
   {
     ut_a(block_index->freed());
+    cursor->flag= BTR_CUR_HASH_FAIL;
     goto block_and_ahi_release_and_fail;
   }
 
@@ -1169,6 +1180,7 @@ btr_search_guess_on_hash(
     default:
     mismatch:
       mtr->release_last_page();
+      cursor->flag= BTR_CUR_HASH_FAIL;
       goto fail;
     }
 
@@ -1183,6 +1195,7 @@ btr_search_guess_on_hash(
     index->search_info.n_hash_potential= n_hash_potential;
 
   index->search_info.last_hash_succ= true;
+  cursor->flag= BTR_CUR_HASH;
 
 #ifdef UNIV_SEARCH_PERF_STAT
   btr_search_n_succ++;

storage/innobase/include/btr0cur.h

@@ -649,6 +649,7 @@ enum btr_cur_method {
 #ifdef BTR_CUR_HASH_ADAPT
 	BTR_CUR_HASH,		/*!< successful shortcut using
 				the hash index */
+	BTR_CUR_HASH_ABORT,	/*!< the hash index could not be used */
 	BTR_CUR_HASH_FAIL,	/*!< failure using hash, success using
 				binary search: the misleading hash
 				reference is stored in the field