commit 3dad1aa3ef91761628cbb31d3920c670fd3478c5
Author: Fangxin Lou <xin.loufx@alibaba-inc.com>
Date:   Sat Mar 7 08:35:19 2020 +0800

    [perf] optimize AHI disable logic
    
    Add disable_in_progress to disable AHI search and maintain first, and
    then start to disable AHI. (see btr_search_disable function)

diff --git a/storage/innobase/btr/btr0sea.cc b/storage/innobase/btr/btr0sea.cc
index 5403a1beec1..32b8d023442 100644
--- a/storage/innobase/btr/btr0sea.cc
+++ b/storage/innobase/btr/btr0sea.cc
@@ -55,6 +55,7 @@ this program; if not, write to the Free Software Foundation, Inc.,
 /** Is search system enabled.
 Search system is protected by array of latches. */
 bool btr_search_enabled = true;
+bool btr_search_disable_in_progress = false;
 
 /** Number of adaptive hash index partition. */
 ulong btr_ahi_parts = 8;
@@ -301,6 +302,10 @@ static void btr_search_disable_ref_count(dict_table_t *table) {
 void btr_search_disable(bool need_mutex) {
   dict_table_t *table;
 
+  /* set disalbe_in_progress and sleep for a while */
+  btr_search_disable_in_progress = true;
+  os_thread_sleep(100000);
+
   if (need_mutex) {
     mutex_enter(&dict_sys->mutex);
   }
@@ -313,11 +318,13 @@ void btr_search_disable(bool need_mutex) {
       mutex_exit(&dict_sys->mutex);
     }
 
+    btr_search_disable_in_progress = false;
     btr_search_x_unlock_all();
     return;
   }
 
   btr_search_enabled = false;
+  btr_search_disable_in_progress = false;
 
   /* Clear the index->search_info->ref_count of every index in
   the data dictionary cache. */
@@ -874,7 +881,7 @@ ibool btr_search_guess_on_hash(dict_index_t *index, btr_search_t *info,
   btr_pcur_t pcur;
 #endif
 
-  if (!btr_search_enabled) {
+  if (!btr_search_enabled || btr_search_disable_in_progress) {
     return (FALSE);
   }
 
@@ -1450,7 +1457,8 @@ static void btr_search_build_page_hash_index(dict_index_t *index,
   ulint offsets_[REC_OFFS_NORMAL_SIZE];
   ulint *offsets = offsets_;
 
-  if (index->disable_ahi || !btr_search_enabled) {
+  if (index->disable_ahi || !btr_search_enabled ||
+      btr_search_disable_in_progress) {
     return;
   }
 
@@ -1622,7 +1630,8 @@ void btr_search_move_or_delete_hash_entries(buf_block_t *new_block,
   /* AHI is disabled for intrinsic table as it depends on index-id
   which is dynamically assigned for intrinsic table indexes and not
   through a centralized index generator. */
-  if (index->disable_ahi || !btr_search_enabled) {
+  if (index->disable_ahi || !btr_search_enabled ||
+      btr_search_disable_in_progress) {
     return;
   }
 
@@ -1684,7 +1693,8 @@ void btr_search_update_hash_on_delete(btr_cur_t *cursor) {
   mem_heap_t *heap = NULL;
   rec_offs_init(offsets_);
 
-  if (cursor->index->disable_ahi || !btr_search_enabled) {
+  if (cursor->index->disable_ahi || !btr_search_enabled ||
+      btr_search_disable_in_progress) {
     return;
   }
 
@@ -1744,7 +1754,8 @@ void btr_search_update_hash_node_on_insert(btr_cur_t *cursor) {
   dict_index_t *index;
   rec_t *rec;
 
-  if (cursor->index->disable_ahi || !btr_search_enabled) {
+  if (cursor->index->disable_ahi || !btr_search_enabled ||
+      btr_search_disable_in_progress) {
     return;
   }
 
@@ -1815,7 +1826,8 @@ void btr_search_update_hash_on_insert(btr_cur_t *cursor) {
   ulint *offsets = offsets_;
   rec_offs_init(offsets_);
 
-  if (cursor->index->disable_ahi || !btr_search_enabled) {
+  if (cursor->index->disable_ahi || !btr_search_enabled ||
+      btr_search_disable_in_progress) {
     return;
   }
 
diff --git a/storage/innobase/include/btr0types.h b/storage/innobase/include/btr0types.h
index d1abed66edc..364db9d3385 100644
--- a/storage/innobase/include/btr0types.h
+++ b/storage/innobase/include/btr0types.h
@@ -50,6 +50,7 @@ struct btr_search_t;
 /** Is search system enabled.
 Search system is protected by array of latches. */
 extern bool btr_search_enabled;
+extern bool btr_search_disable_in_progress;
 
 /** Number of adaptive hash index partition. */
 extern ulong btr_ahi_parts;
diff --git a/storage/innobase/row/row0sel.cc b/storage/innobase/row/row0sel.cc
index c60fd6ae063..79fee6a0dd0 100644
--- a/storage/innobase/row/row0sel.cc
+++ b/storage/innobase/row/row0sel.cc
@@ -4481,6 +4481,7 @@ dberr_t row_search_mvcc(byte *buf, page_cur_mode_t mode,
   may be long and there may be externally stored fields */
 
   if (UNIV_UNLIKELY(direction == 0) && unique_search && btr_search_enabled &&
+      !btr_search_disable_in_progress &&
       index->is_clustered() && !prebuilt->templ_contains_blob &&
       !prebuilt->used_in_HANDLER &&
       (prebuilt->mysql_row_len < UNIV_PAGE_SIZE / 8) && !prebuilt->innodb_api) {