read-only performance regression in 10.6

--------------------------------------------------------------------------------

Test 't_1K-reads-innodb-multi' - sysbench OLTP readonly

1000 point selects per iteration, no range queries

20 tables, 1 mio rows total, engine InnoDB/XtraDB (builtin)

numbers are queries per second

#thread count           1       8       16      32      64      128     256

mariadb-10.5.6          17829   121710  198138  323747  322578  325941  320516

mariadb-10.5.7          17909   123676  196655  322730  319521  321345  317861

mariadb-10.5.8          17323   122421  194577  323129  321011  322180  318691

mariadb-10.5.9          17908   121776  195502  319654  316815  321072  315318

mariadb-10.6.0          16571   114360  187503  309040  306141  308083  304082

--------------------------------------------------------------------------------

Test 't_collate_distinct_range_utf8_unicode' - sysbench OLTP readonly

selecting distinct rows from short range, collation utf8_unicode_ci

1 table, 1 mio rows, engine InnoDB/XtraDB (builtin)

numbers are queries per second

#thread count           1       8       16      32      64      128     256

mariadb-10.5.6          7802.2  52344   90565   143215  143131  143469  142597

mariadb-10.5.7          7661.6  51889   89530   141981  141824  142293  141383

mariadb-10.5.8          7606.1  52009   90159   141161  142194  142386  141560

mariadb-10.5.9          7561.6  51927   90081   142035  142127  142333  141701

mariadb-10.6.0          7121.8  48368   84864   136162  135595  135270  134618