LP:637160 - Seven-fold performance regression with maria-5.3-dsmrr-cpk

The following query:

SELECT table1 . `col_int_key` AS field1 FROM ( E AS table1 STRAIGHT_JOIN ( ( DD AS table2 INNER JOIN E AS table3 ON (table3 . `col_int_nokey` = table2 . `pk` ) ) ) ON (table3 . `col_varchar_nokey` > table2 . `col_varchar_key` ) ) LIMIT 8786;

Takes less than 0.1 seconds on maria-5.3 and more than 0.7 seconds on maria-5.3-dsmrr-cpk with mrr_sort_keys=ON, and many minutes with maria_sort_keys=OFF.

The query demonstrates both A) the performance regression as a ratio between the current running time and the new running time and B) the fact that a previously instantaneous query now takes a period of time that would be noticed by the user.