PS-9297 Lost a record while scanning in reverse order on cursor

https://perconadev.atlassian.net/browse/PS-9297

Problem
========
If the last user record on the prev leaf is pessimistically updated during move_backward_from_page, the record may be deleted from the prev leaf and reinserted into the current page. Scanning in reverse order will miss this record.

Cause
========
Same as PS-9092, move_backward_from_page cannot sense that records are moved from the prev leaf to the current leaf.

Solution
========
If btr_insert_into_right_sibling causes records to move between pages, prevent the next page from being optimistically accessed

mysql-test/suite/innodb/r/percona_bug_ps9297.result

@@ -0,0 +1,42 @@
+create table c(id int primary key, val varchar(8000));
+insert into c values (1,repeat('a',3000));
+insert into c values (2,repeat('a',3000));
+insert into c values (3,repeat('a',3000));
+insert into c values (4,repeat('a',3000));
+insert into c values (5,repeat('a',3000));
+insert into c values (-1,repeat('a',2000));
+insert into c values (-2,repeat('a',2000));
+insert into c values (-3,repeat('a',2000));
+insert into c values (-4,repeat('a',2000));
+insert into c values (-5,repeat('a',2000));
+select id,length(val) from c order by id desc;
+id	length(val)
+5	3000
+4	3000
+3	3000
+2	3000
+1	3000
+-1	2000
+-2	2000
+-3	2000
+-4	2000
+-5	2000
+set DEBUG="+d,desc_scan_debug";
+set DEBUG_SYNC="desc_scan_before_restore_position SIGNAL desc_scan_before_restore_position_done WAIT_FOR continue";
+select id,length(val) from c order by id desc;
+set DEBUG_SYNC="now WAIT_FOR desc_scan_before_restore_position_done";
+update c set val=repeat('b',6000) where id=2;
+set DEBUG_SYNC="now SIGNAL continue";
+id	length(val)
+5	3000
+4	3000
+3	3000
+2	3000
+1	3000
+-1	2000
+-2	2000
+-3	2000
+-4	2000
+-5	2000
+set DEBUG="-d,desc_scan_debug";
+drop table c;

mysql-test/suite/innodb/t/percona_bug_ps9297.test

@@ -0,0 +1,31 @@
+--source include/have_debug.inc
+
+connect (con1, localhost, root,,);
+--connection default
+create table c(id int primary key, val varchar(8000));
+insert into c values (1,repeat('a',3000));
+insert into c values (2,repeat('a',3000));
+insert into c values (3,repeat('a',3000));
+insert into c values (4,repeat('a',3000));
+insert into c values (5,repeat('a',3000));
+
+insert into c values (-1,repeat('a',2000));
+insert into c values (-2,repeat('a',2000));
+insert into c values (-3,repeat('a',2000));
+insert into c values (-4,repeat('a',2000));
+insert into c values (-5,repeat('a',2000));
+
+--connection con1
+select id,length(val) from c order by id desc;
+set DEBUG="+d,desc_scan_debug";
+set DEBUG_SYNC="desc_scan_before_restore_position SIGNAL desc_scan_before_restore_position_done WAIT_FOR continue";
+send select id,length(val) from c order by id desc;
+--connection default
+set DEBUG_SYNC="now WAIT_FOR desc_scan_before_restore_position_done";
+update c set val=repeat('b',6000) where id=2;
+set DEBUG_SYNC="now SIGNAL continue";
+--connection con1
+reap;
+set DEBUG="-d,desc_scan_debug";
+--connection default
+drop table c;

storage/innobase/btr/btr0btr.cc

@@ -2313,6 +2313,11 @@ static rec_t *btr_insert_into_right_sibling(uint32_t flags, btr_cur_t *cursor,
     }
   }
 
+  /** We moved the record from the current page to the next page. Therefore, we
+   * need to disable optimistic access to the next page to ensure that the
+   * record will not be mistakenly skipped during reverse scanning on cursor. */
+  buf_block_modify_clock_inc(next_block);
+
   return (rec);
 }
 

storage/innobase/btr/btr0pcur.cc

@@ -419,6 +419,12 @@ void btr_pcur_t::move_backward_from_page(mtr_t *mtr) {
 
   mtr_commit(mtr);
 
+  DBUG_EXECUTE_IF("desc_scan_debug", {
+    if (strcmp(index()->table_name, "test/c") == 0) {
+      DEBUG_SYNC_C("desc_scan_before_restore_position");
+    }
+  });
+
   mtr_start(mtr);
 
   restore_position(latch_mode2, mtr, UT_LOCATION_HERE);