MDEV-23380 InnoDB reads a page from disk despite parsing MLOG_INIT_FI…

…LE_PAGE2 record

This problem is caused by 6697135
(MDEV-21572). During recovery, InnoDB prefetches the siblings of
change buffer index leaf page. It does asynchronous page read
and recovery scenario wasn't handled in buf_read_page_background().
It leads to the refusal of startup of the server.

Solution:
=========
  InnoDB shouldn't allow the change buffer index page siblings
to be prefetched.

storage/innobase/btr/btr0cur.cc

@@ -3145,7 +3145,7 @@ btr_cur_optimistic_insert(
 
 		/* prefetch siblings of the leaf for the pessimistic
 		operation, if the page is leaf. */
-		if (page_is_leaf(page)) {
+		if (page_is_leaf(page) && !index->is_ibuf()) {
 			btr_cur_prefetch_siblings(block);
 		}
 fail_err:
@@ -4041,6 +4041,7 @@ btr_cur_optimistic_update(
 
 	if (rec_offs_any_extern(*offsets)) {
 any_extern:
+		ut_ad(!index->is_ibuf());
 		/* Externally stored fields are treated in pessimistic
 		update */
 
@@ -4220,7 +4221,7 @@ btr_cur_optimistic_update(
 		}
 	}
 
-	if (err != DB_SUCCESS) {
+	if (err != DB_SUCCESS && !index->is_ibuf()) {
 		/* prefetch siblings of the leaf for the pessimistic
 		operation. */
 		btr_cur_prefetch_siblings(block);

storage/innobase/include/dict0mem.h

@@ -1034,6 +1034,9 @@ struct dict_index_t{
     }
   }
 
+  /** @return whether this is the change buffer */
+  bool is_ibuf() const { return UNIV_UNLIKELY(type & DICT_IBUF); }
+
 #ifdef BTR_CUR_HASH_ADAPT
   /** @return a clone of this */
   dict_index_t* clone() const;