Redundant clustered lookups in covering scans when holding a table X-lock

CREATE TABLE t1 (id INT PRIMARY KEY, sec INT, pad CHAR(100), KEY i1(sec))

ENGINE=InnoDB;

INSERT INTO t1 SELECT seq, seq, seq FROM seq_1_to_10000;

SELECT sec,id FROM t1 FOR UPDATE;

/* in row_search_mvcc: */

	if (index != clust_index && prebuilt->need_to_access_clustered) {

		if (row_search_with_covering_prefix(prebuilt, rec, offsets)) {

			goto use_covering_index;

		}

requires_clust_rec:

/* in row_search_with_covering_prefix: */

	/* In ha_innobase::build_template() we choose to access the

	whole row when using exclusive row locks or In case of fts

	query, we need to read from clustered index */

	if (prebuilt->select_lock_type == LOCK_X || prebuilt->in_fts_query

	    || !index->is_btree()) {

		return false;

	}

--source include/have_innodb.inc

--source include/have_sequence.inc

SET GLOBAL innodb_monitor_enable='lock_rec_lock_created';

CREATE TABLE t1 (id INT PRIMARY KEY, sec INT, pad CHAR(100), KEY i1(sec))

ENGINE=InnoDB;

INSERT INTO t1 SELECT seq, seq, seq FROM seq_1_to_10000;

let $bp= SELECT VARIABLE_VALUE FROM information_schema.GLOBAL_STATUS

         WHERE VARIABLE_NAME='INNODB_BUFFER_POOL_READ_REQUESTS';

let $lk= SELECT COUNT FROM information_schema.INNODB_METRICS

         WHERE NAME='lock_rec_lock_created';

set innodb_table_lock_on_full_scan=0;

let $r1= `$bp`;

let $l1= `$lk`;

--disable_result_log

SELECT sec,id FROM t1 FOR UPDATE;

--enable_result_log

let $r2= `$bp`;

let $l2= `$lk`;

--disable_result_log

SELECT sec,id FROM t1 LOCK IN SHARE MODE;

--enable_result_log

let $r3= `$bp`;

let $l3= `$lk`;

set innodb_table_lock_on_full_scan=1;

--disable_result_log

SELECT sec,id FROM t1 FOR UPDATE;

--enable_result_log

let $r4= `$bp`;

let $l4= `$lk`;

--disable_result_log

SELECT sec,id FROM t1 LOCK IN SHARE MODE;

--enable_result_log

let $r5= `$bp`;

let $l5= `$lk`;

--echo # read requests

eval SELECT ($r2 - $r1) as x_off, ($r3 - $r2) as s_off,  ($r4 - $r3) as x_on, ($r5 - $r4) as s_on;

--echo # locks

eval SELECT ($l2 - $l1) as x_off, ($l3 - $l2) as s_off,  ($l4 - $l3) as x_on, ($l5 - $l4) as s_on;

DROP TABLE t1;

SET GLOBAL innodb_monitor_enable=default;

# read requests

#  [... 1 lines elided]

x_off	s_off	x_on	s_on

20011	11	20011	11

# locks

#  [... 1 lines elided]

x_off	s_off	x_on	s_on

96	10	0	0