BUG#22385442 - INNODB: DIFFICULT TO FIND FREE BLOCKS IN THE BUFFER POOL

Problem:
We keep pinning pages in dict_stats_analyze_index_below_cur(),
but doesn't release these pages. When we have a relative small
buffer pool size, and big innodb_stats_persistent_sample_pages,
there will be no free pages for use.

Solution:
Use a separate mtr in dict_stats_analyze_index_below_cur(),
and commit mtr before return.
Reviewed-by: Jimmy Yang <jimmy.yang@oracle.com>
RB: 11362

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

+CREATE PROCEDURE populate_t1()
+BEGIN
+DECLARE i int DEFAULT 1;
+START TRANSACTION;
+WHILE (i <= 1000000) DO
+INSERT INTO t1 VALUES (i, i, CONCAT('a', i));
+SET i = i + 1;
+END WHILE;
+COMMIT;
+END|
+CREATE TABLE t1(
+class   INT,
+id      INT,
+title   VARCHAR(100)
+) ENGINE=InnoDB;
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+1000000
+SET GLOBAL innodb_stats_persistent_sample_pages=2000;
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+DROP TABLE t1;
+DROP PROCEDURE populate_t1;
+SET GLOBAL innodb_stats_persistent_sample_pages=default;

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

+#
+# BUG#22385442 - INNODB: DIFFICULT TO FIND FREE BLOCKS IN THE BUFFER POOL
+#
+
+--source include/have_innodb.inc
+--source include/big_test.inc
+
+DELIMITER |;
+CREATE PROCEDURE populate_t1()
+BEGIN
+        DECLARE i int DEFAULT 1;
+
+        START TRANSACTION;
+        WHILE (i <= 1000000) DO
+                INSERT INTO t1 VALUES (i, i, CONCAT('a', i));
+                SET i = i + 1;
+        END WHILE;
+        COMMIT;
+END|
+DELIMITER ;|
+
+CREATE TABLE t1(
+        class   INT,
+        id      INT,
+        title   VARCHAR(100)
+) ENGINE=InnoDB;
+
+-- disable_query_log
+CALL populate_t1();
+-- enable_query_log
+
+SELECT COUNT(*) FROM t1;
+
+SET GLOBAL innodb_stats_persistent_sample_pages=2000;
+
+ANALYZE TABLE t1;
+
+DROP TABLE t1;
+
+DROP PROCEDURE populate_t1;
+
+SET GLOBAL innodb_stats_persistent_sample_pages=default;