Back-ported the patch of the mysql-5.6 code line that

fixed several defects in the greedy optimization:

1) The greedy optimizer calculated the 'compare-cost' (CPU-cost)
   for iterating over the partial plan result at each level in
   the query plan as 'record_count / (double) TIME_FOR_COMPARE'

   This cost was only used locally for 'best' calculation at each
   level, and *not* accumulated into the total cost for the query plan.

   This fix added the 'CPU-cost' of processing 'current_record_count'
   records at each level to 'current_read_time' *before* it is used as
   'accumulated cost' argument to recursive 
   best_extension_by_limited_search() calls. This ensured that the
   cost of a huge join-fanout early in the QEP was correctly
   reflected in the cost of the final QEP.

   To get identical cost for a 'best' optimized query and a
   straight_join with the same join order, the same change was also
   applied to optimize_straight_join() and get_partial_join_cost()

2) Furthermore to get equal cost for 'best' optimized query and a
   straight_join the new code substrcated the same '0.001' in
   optimize_straight_join() as it had been already done in
   best_extension_by_limited_search()

3) When best_extension_by_limited_search() aggregated the 'best' plan a
   plan was 'best' by the check :

   'if ((search_depth == 1) || (current_read_time < join->best_read))'

   The term '(search_depth == 1' incorrectly caused a new best plan to be
   collected whenever the specified 'search_depth' was reached - even if
   this partial query plan was more expensive than what we had already
   found.

1 files changed, 2 insertions, 2 deletions

diff --git a/mysql-test/r/subselect2.result b/mysql-test/r/subselect2.result
index 52297a65e39..41c445329cb 100644
--- a/mysql-test/r/subselect2.result
+++ b/mysql-test/r/subselect2.result
@@ -125,9 +125,9 @@ DOCID	DOCNAME	DOCTYPEID	FOLDERID	AUTHOR	CREATED	TITLE	SUBTITLE	DOCABSTRACT	PUBLI
 c373e9f5ad07993f3859444553544200	Last Discussion	c373e9f5ad079174ff17444553544200	c373e9f5ad0796c0eca4444553544200	Goldilocks	2003-06-09 11:21:06	Title: Last Discussion	NULL	Setting new abstract and keeping doc checked out	2003-06-09 10:51:26	2003-06-09 10:51:26	NULL	NULL	NULL	03eea05112b845949f3fd03278b5fe43	2003-06-09 11:21:06	admin	0	NULL	Discussion	NULL	NULL
 EXPLAIN SELECT t2.*, t4.DOCTYPENAME, t1.CONTENTSIZE,t1.MIMETYPE FROM t2 INNER JOIN t4 ON t2.DOCTYPEID = t4.DOCTYPEID LEFT OUTER JOIN t1 ON t2.DOCID = t1.DOCID WHERE t2.FOLDERID IN(SELECT t3.FOLDERID FROM t3 WHERE t3.PARENTID IN(SELECT t3.FOLDERID FROM t3 WHERE t3.PARENTID IN(SELECT t3.FOLDERID FROM t3 WHERE t3.PARENTID IN(SELECT t3.FOLDERID FROM t3 WHERE t3.PARENTID IN(SELECT t3.FOLDERID FROM t3 WHERE t3.PARENTID='2f6161e879db43c1a5b82c21ddc49089' AND t3.FOLDERNAME = 'Level1') AND t3.FOLDERNAME = 'Level2') AND t3.FOLDERNAME = 'Level3') AND t3.FOLDERNAME = 'CopiedFolder') AND t3.FOLDERNAME = 'Movie Reviews') AND t2.DOCNAME = 'Last Discussion';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t4	ALL	PRIMARY	NULL	NULL	NULL	10	
-1	PRIMARY	t2	ALL	DDOCTYPEID_IDX,DFOLDERID_IDX	NULL	NULL	NULL	9	Using where; Using join buffer (flat, BNL join)
+1	PRIMARY	t2	ALL	DDOCTYPEID_IDX,DFOLDERID_IDX	NULL	NULL	NULL	9	Using where
 1	PRIMARY	t1	eq_ref	PRIMARY	PRIMARY	34	test.t2.DOCID	1	
+1	PRIMARY	t4	eq_ref	PRIMARY	PRIMARY	34	test.t2.DOCTYPEID	1	
 1	PRIMARY	t3	eq_ref	PRIMARY,FFOLDERID_IDX,CMFLDRPARNT_IDX	PRIMARY	34	test.t2.FOLDERID	1	Using where
 1	PRIMARY	t3	eq_ref	PRIMARY,FFOLDERID_IDX,CMFLDRPARNT_IDX	PRIMARY	34	test.t3.PARENTID	1	Using where
 1	PRIMARY	t3	eq_ref	PRIMARY,FFOLDERID_IDX,CMFLDRPARNT_IDX	PRIMARY	34	test.t3.PARENTID	1	Using where