Added thread variable max_seeks_for_key

Change optimizer to prefer key lookups before table scan
Change table scans to be done after tables with constrains on scanned table 


mysql-test/r/distinct.result:
  Update results
mysql-test/r/group_by.result:
  Update results
mysql-test/r/heap.result:
  Update results
mysql-test/r/join.result:
  Update results
mysql-test/r/key_diff.result:
  Update results
mysql-test/r/myisam.result:
  Update results
mysql-test/r/order_by.result:
  Update results
mysql-test/r/select_safe.result:
  Update results
mysql-test/t/distinct.test:
  Change test to be repeatable
mysql-test/t/join.test:
  Change test to be repeatable
mysql-test/t/select_safe.test:
  Add tests for MAX_SEEKS_FOR_KEY
sql/handler.h:
  Optimize structure for 64 bit machines (and to avoid problems with gdb)
sql/item_cmpfunc.cc:
  Initialize not_null_tables_cache properly
sql/mysqld.cc:
  Added max_seeks_for_key
sql/set_var.cc:
  Added max_seeks_for_key
sql/sql_class.h:
  Added max_seeks_for_key
sql/sql_select.cc:
  Added max_seeks_for_key
  Change optimizer to prefer key lookups before table scan.
  Change table scans to be done after tables with constrains on scanned table

17 files changed, 114 insertions, 65 deletions

diff --git a/mysql-test/r/distinct.result b/mysql-test/r/distinct.result
index 5f4f7cced1e..53a20eeea0b 100644
--- a/mysql-test/r/distinct.result
+++ b/mysql-test/r/distinct.result
@@ -161,7 +161,7 @@ SELECT DISTINCT UserId FROM t1 WHERE UserId=22;
 UserId
 drop table t1;
 CREATE TABLE t1 (a int(10) unsigned not null primary key,b int(10) unsigned);
-INSERT INTO t1 VALUES (1,1),(2,1);
+INSERT INTO t1 VALUES (1,1),(2,1),(3,1),(4,1);
 CREATE TABLE t2 (a int(10) unsigned not null, key (A));
 INSERT INTO t2 VALUES (1),(2);
 CREATE TABLE t3 (a int(10) unsigned, key(A), b text);
@@ -189,7 +189,7 @@ insert into t4 select * from t3;
 insert into t3 select * from t4;
 explain select distinct t1.a from t1,t3 where t1.a=t3.a;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	index	PRIMARY	PRIMARY	4	NULL	2	Using index; Using temporary
+t1	index	PRIMARY	PRIMARY	4	NULL	4	Using index; Using temporary
 t3	ref	a	a	5	t1.a	10	Using where; Using index; Distinct
 select distinct t1.a from t1,t3 where t1.a=t3.a;
 a
@@ -200,16 +200,16 @@ select distinct 1 from t1,t3 where t1.a=t3.a;
 1
 explain SELECT distinct t1.a from t1;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	index	NULL	PRIMARY	4	NULL	2	Using index
+t1	index	NULL	PRIMARY	4	NULL	4	Using index
 explain SELECT distinct t1.a from t1 order by a desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	index	NULL	PRIMARY	4	NULL	2	Using index
+t1	index	NULL	PRIMARY	4	NULL	4	Using index
 explain SELECT t1.a from t1 group by a order by a desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	index	NULL	PRIMARY	4	NULL	2	Using index
+t1	index	NULL	PRIMARY	4	NULL	4	Using index
 explain SELECT distinct t1.a from t1 order by a desc limit 1;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	index	NULL	PRIMARY	4	NULL	2	Using index
+t1	index	NULL	PRIMARY	4	NULL	4	Using index
 explain SELECT distinct a from t3 order by a desc limit 2;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t3	index	NULL	a	5	NULL	204	Using index
diff --git a/mysql-test/r/group_by.result b/mysql-test/r/group_by.result
index 94e1ce59585..67e6bec09f6 100644
--- a/mysql-test/r/group_by.result
+++ b/mysql-test/r/group_by.result
@@ -534,11 +534,11 @@ a	b
 explain select t1.a,t2.b from t1,t2 where t1.a=t2.a group by t1.a,t2.b;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	NULL	NULL	NULL	NULL	6	Using temporary; Using filesort
-t2	ALL	a	NULL	NULL	NULL	4	Using where
+t2	ALL	a	NULL	NULL	NULL	3	Using where
 explain select t1.a,t2.b from t1,t2 where t1.a=t2.a group by t1.a,t2.b ORDER BY NULL;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	NULL	NULL	NULL	NULL	6	Using temporary
-t2	ALL	a	NULL	NULL	NULL	4	Using where
+t2	ALL	a	NULL	NULL	NULL	3	Using where
 drop table t1,t2;
 create table t1 (a int, b int);
 insert into t1 values (1, 4),(10, 40),(1, 4),(10, 43),(1, 4),(10, 41),(1, 4),(10, 43),(1, 4);
diff --git a/mysql-test/r/heap.result b/mysql-test/r/heap.result
index d8905085e34..a04ddf3f302 100644
--- a/mysql-test/r/heap.result
+++ b/mysql-test/r/heap.result
@@ -166,7 +166,7 @@ alter table t1 add column new_col char(1) not null, add key (btn,new_col), drop
 update t1 set new_col=btn;
 explain select * from t1 where btn="a";
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	ALL	btn	NULL	NULL	NULL	14	Using where
+t1	ALL	btn	NULL	NULL	NULL	11	Using where
 explain select * from t1 where btn="a" and new_col="a";
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ref	btn	btn	11	const,const	10	Using where
diff --git a/mysql-test/r/join.result b/mysql-test/r/join.result
index e063b5c3e02..039b6e1cba3 100644
--- a/mysql-test/r/join.result
+++ b/mysql-test/r/join.result
@@ -104,9 +104,7 @@ KEY category (category,county,state)
 INSERT INTO t2 VALUES (3,2,11,12,5400,7800);
 INSERT INTO t2 VALUES (4,2,25,12,6500,11200);
 INSERT INTO t2 VALUES (5,1,37,6,10000,12000);
-select a.id, b.category as catid, b.state as stateid, b.county as
-countyid from t1 a, t2 b where (a.token =
-'a71250b7ed780f6ef3185bfffe027983') and (a.count = b.id);
+select a.id, b.category as catid, b.state as stateid, b.county as countyid from t1 a, t2 b ignore index (primary) where (a.token ='a71250b7ed780f6ef3185bfffe027983') and (a.count = b.id);
 id	catid	stateid	countyid
 27	2	12	11
 28	2	12	11
diff --git a/mysql-test/r/key_diff.result b/mysql-test/r/key_diff.result
index 4eaccc696f9..2d4bc19474f 100644
--- a/mysql-test/r/key_diff.result
+++ b/mysql-test/r/key_diff.result
@@ -36,7 +36,7 @@ a	a	a	a
 explain select t1.*,t2.* from t1,t1 as t2 where t1.A=t2.B;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	a	NULL	NULL	NULL	5	
-t2	ALL	b	NULL	NULL	NULL	5	Using where
+t2	ALL	b	NULL	NULL	NULL	4	Using where
 select t1.*,t2.* from t1,t1 as t2 where t1.A=t2.B order by binary t1.a,t2.a;
 a	b	a	b
 A	B	a	a
diff --git a/mysql-test/r/myisam.result b/mysql-test/r/myisam.result
index 9a653aff99e..c4368384bf8 100644
--- a/mysql-test/r/myisam.result
+++ b/mysql-test/r/myisam.result
@@ -335,12 +335,12 @@ t1	1	c_2	1	c	A	5	NULL	NULL	YES	BTREE
 t1	1	c_2	2	a	A	5	NULL	NULL		BTREE	
 explain select * from t1,t2 where t1.a=t2.a;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	ALL	a	NULL	NULL	NULL	5	
-t2	ALL	a	NULL	NULL	NULL	2	Using where
+t2	ALL	a	NULL	NULL	NULL	2	
+t1	ALL	a	NULL	NULL	NULL	4	Using where
 explain select * from t1,t2 force index(a) where t1.a=t2.a;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t2	ALL	a	NULL	NULL	NULL	2	
-t1	ALL	a	NULL	NULL	NULL	5	Using where
+t1	ALL	a	NULL	NULL	NULL	4	Using where
 explain select * from t1 force index(a),t2 force index(a) where t1.a=t2.a;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t2	ALL	a	NULL	NULL	NULL	2	
@@ -351,8 +351,8 @@ t2	ALL	b	NULL	NULL	NULL	2
 t1	ref	b	b	5	t2.b	1	Using where
 explain select * from t1,t2 force index(c) where t1.a=t2.a;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	ALL	a	NULL	NULL	NULL	5	
-t2	ALL	NULL	NULL	NULL	NULL	2	Using where
+t2	ALL	NULL	NULL	NULL	NULL	2	
+t1	ALL	a	NULL	NULL	NULL	4	Using where
 explain select * from t1 where a=0 or a=2;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	a	NULL	NULL	NULL	5	Using where
diff --git a/mysql-test/r/order_by.result b/mysql-test/r/order_by.result
index ff2dd93311c..64fac8af872 100644
--- a/mysql-test/r/order_by.result
+++ b/mysql-test/r/order_by.result
@@ -307,17 +307,17 @@ table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	range	a	a	9	NULL	8	Using where; Using index
 explain select * from t1 where a = 2 and b >0 order by a desc,b desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	range	a	a	9	NULL	5	Using where; Using index
+t1	range	a	a	9	NULL	4	Using where; Using index
 explain select * from t1 where a = 2 and b is null order by a desc,b desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ref	a	a	9	const,const	1	Using where; Using index; Using filesort
 explain select * from t1 where a = 2 and (b is null or b > 0) order by a
 desc,b desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	range	a	a	9	NULL	6	Using where; Using index
+t1	range	a	a	9	NULL	5	Using where; Using index
 explain select * from t1 where a = 2 and b > 0 order by a desc,b desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	range	a	a	9	NULL	5	Using where; Using index
+t1	range	a	a	9	NULL	4	Using where; Using index
 explain select * from t1 where a = 2 and b < 2 order by a desc,b desc;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	range	a	a	9	NULL	2	Using where; Using index
diff --git a/mysql-test/r/select_safe.result b/mysql-test/r/select_safe.result
index 3303f19d9c7..830390ebe3c 100644
--- a/mysql-test/r/select_safe.result
+++ b/mysql-test/r/select_safe.result
@@ -1,6 +1,6 @@
 drop table if exists t1;
 SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=4, SQL_MAX_JOIN_SIZE=9;
-create table t1 (a int auto_increment primary key, b char(20));
+create table t1 (a int auto_increment primary key, b char(20), key(b));
 insert into t1 values(1,"test");
 SELECT SQL_BUFFER_RESULT * from t1;
 a	b
@@ -13,7 +13,7 @@ a	b
 1	test
 2	test2
 update t1 set b="a" where a=1;
-select 1 from t1,t1 as t2,t1 as t3,t1 as t4;
+select 1 from t1,t1 as t2,t1 as t3;
 1
 1
 1
@@ -22,11 +22,9 @@ select 1 from t1,t1 as t2,t1 as t3,t1 as t4;
 update t1 set b="a";
 You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
 update t1 set b="a" where b="test";
-You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
 delete from t1;
 You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
 delete from t1 where b="test";
-You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
 delete from t1 where a+0=1;
 You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
 select 1 from t1,t1 as t2,t1 as t3,t1 as t4,t1 as t5;
@@ -59,5 +57,22 @@ a	b
 2	test2
 4	a
 5	a
+SELECT @@MAX_SEEKS_FOR_KEY;
+@@max_seeks_for_key
+4294967295
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a");
+explain select * from t1,t1 as t2 where t1.b=t2.b;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	ALL	b	NULL	NULL	NULL	21	
+t2	ALL	b	NULL	NULL	NULL	16	Using where
+set MAX_SEEKS_FOR_KEY=1;
+explain select * from t1,t1 as t2 where t1.b=t2.b;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	ALL	b	NULL	NULL	NULL	21	
+t2	ref	b	b	21	t1.b	6	Using where
+SET MAX_SEEKS_FOR_KEY=DEFAULT;
 drop table t1;
 SET SQL_SAFE_UPDATES=0,SQL_SELECT_LIMIT=DEFAULT, SQL_MAX_JOIN_SIZE=DEFAULT;
diff --git a/mysql-test/t/distinct.test b/mysql-test/t/distinct.test
index 7f75b6b1687..ecce2409571 100644
--- a/mysql-test/t/distinct.test
+++ b/mysql-test/t/distinct.test
@@ -60,7 +60,7 @@ drop table t1;
 #
 
 CREATE TABLE t1 (a int(10) unsigned not null primary key,b int(10) unsigned);
-INSERT INTO t1 VALUES (1,1),(2,1);
+INSERT INTO t1 VALUES (1,1),(2,1),(3,1),(4,1);
 CREATE TABLE t2 (a int(10) unsigned not null, key (A));
 INSERT INTO t2 VALUES (1),(2);
 CREATE TABLE t3 (a int(10) unsigned, key(A), b text);
diff --git a/mysql-test/t/join.test b/mysql-test/t/join.test
index 08cc5731723..19e04d2aa7e 100644
--- a/mysql-test/t/join.test
+++ b/mysql-test/t/join.test
@@ -98,10 +98,7 @@ CREATE TABLE t2 (
 INSERT INTO t2 VALUES (3,2,11,12,5400,7800);
 INSERT INTO t2 VALUES (4,2,25,12,6500,11200);
 INSERT INTO t2 VALUES (5,1,37,6,10000,12000);
-
-select a.id, b.category as catid, b.state as stateid, b.county as
-countyid from t1 a, t2 b where (a.token =
-'a71250b7ed780f6ef3185bfffe027983') and (a.count = b.id);
+select a.id, b.category as catid, b.state as stateid, b.county as countyid from t1 a, t2 b ignore index (primary) where (a.token ='a71250b7ed780f6ef3185bfffe027983') and (a.count = b.id);
 select a.id, b.category as catid, b.state as stateid, b.county as
 countyid from t1 a, t2 b where (a.token =
 'a71250b7ed780f6ef3185bfffe027983') and (a.count = b.id) order by a.id;
diff --git a/mysql-test/t/select_safe.test b/mysql-test/t/select_safe.test
index a085cfee29d..049a35aa355 100644
--- a/mysql-test/t/select_safe.test
+++ b/mysql-test/t/select_safe.test
@@ -4,7 +4,7 @@
 
 drop table if exists t1;
 SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=4, SQL_MAX_JOIN_SIZE=9;
-create table t1 (a int auto_increment primary key, b char(20));
+create table t1 (a int auto_increment primary key, b char(20), key(b));
 insert into t1 values(1,"test");
 SELECT SQL_BUFFER_RESULT * from t1;
 update t1 set b="a" where a=1;
@@ -12,7 +12,7 @@ delete from t1 where a=1;
 insert into t1 values(1,"test"),(2,"test2");
 SELECT SQL_BUFFER_RESULT * from t1;
 update t1 set b="a" where a=1;
-select 1 from t1,t1 as t2,t1 as t3,t1 as t4;
+select 1 from t1,t1 as t2,t1 as t3;
 
 # The following should give errors:
 --error 1175
@@ -49,6 +49,17 @@ SELECT * from t1;
 SET MAX_JOIN_SIZE=DEFAULT;
 SELECT * from t1;
 
+#
+# Test MAX_SEEKS_FOR_KEY
+#
+SELECT @@MAX_SEEKS_FOR_KEY;
+analyze table t1;
+insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a");
+explain select * from t1,t1 as t2 where t1.b=t2.b;
+set MAX_SEEKS_FOR_KEY=1;
+explain select * from t1,t1 as t2 where t1.b=t2.b;
+SET MAX_SEEKS_FOR_KEY=DEFAULT;
+
 drop table t1;
 
 SET SQL_SAFE_UPDATES=0,SQL_SELECT_LIMIT=DEFAULT, SQL_MAX_JOIN_SIZE=DEFAULT;
diff --git a/sql/handler.h b/sql/handler.h
index 56f63d1d521..dfcfa44fbcd 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -184,40 +184,41 @@ class handler :public Sql_alloc
 {
  protected:
   struct st_table *table;		/* The table definition */
-  uint  active_index;
 
 public:
   byte *ref;				/* Pointer to current row */
   byte *dupp_ref;			/* Pointer to dupp row */
-  uint ref_length;			/* Length of ref (1-8 or the clustered
-					key length) */
-  uint block_size;			/* index block size */
-  ha_rows records;			/* Records i datafilen */
-  ha_rows deleted;			/* Deleted records */
   ulonglong data_file_length;		/* Length off data file */
   ulonglong max_data_file_length;	/* Length off data file */
   ulonglong index_file_length;
   ulonglong max_index_file_length;
   ulonglong delete_length;		/* Free bytes */
   ulonglong auto_increment_value;
-  uint raid_type,raid_chunks;
+  ha_rows records;			/* Records in table */
+  ha_rows deleted;			/* Deleted records */
   ulong raid_chunksize;
-  uint errkey;				/* Last dup key */
-  uint sortkey, key_used_on_scan;
+  ulong mean_rec_length;		/* physical reclength */
   time_t create_time;			/* When table was created */
   time_t check_time;
   time_t update_time;
-  ulong mean_rec_length;		/* physical reclength */
+  uint errkey;				/* Last dup key */
+  uint sortkey, key_used_on_scan;
+  uint active_index;
+  /* Length of ref (1-8 or the clustered key length) */
+  uint ref_length;
+  uint block_size;			/* index block size */
+  uint raid_type,raid_chunks;
   FT_INFO *ft_handler;
   bool  auto_increment_column_changed;
 
-  handler(TABLE *table_arg) : table(table_arg),active_index(MAX_REF_PARTS),
-    ref(0),ref_length(sizeof(my_off_t)), block_size(0),records(0),deleted(0),
-    data_file_length(0), max_data_file_length(0), index_file_length(0),
-    delete_length(0), auto_increment_value(0), raid_type(0),
-    key_used_on_scan(MAX_KEY),
-    create_time(0), check_time(0), update_time(0), mean_rec_length(0),
-    ft_handler(0)
+  handler(TABLE *table_arg) :table(table_arg),
+    ref(0), data_file_length(0), max_data_file_length(0), index_file_length(0),
+    delete_length(0), auto_increment_value(0),
+    records(0), deleted(0), mean_rec_length(0),
+    create_time(0), check_time(0), update_time(0),
+    key_used_on_scan(MAX_KEY), active_index(MAX_REF_PARTS),
+    ref_length(sizeof(my_off_t)), block_size(0),
+    raid_type(0), ft_handler(0)
     {}
   virtual ~handler(void) {}
   int ha_open(const char *name, int mode, int test_if_locked);
@@ -227,7 +228,7 @@ public:
   uint get_dup_key(int error);
   void change_table_ptr(TABLE *table_arg) { table=table_arg; }
   virtual double scan_time()
-    { return ulonglong2double(data_file_length) / IO_SIZE + 1; }
+    { return ulonglong2double(data_file_length) / IO_SIZE + 2; }
   virtual double read_time(uint index, uint ranges, ha_rows rows)
  { return rows2double(ranges+rows); }
   virtual bool fast_key_read() { return 0;}
diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index 770fe3c0232..78a63d84c61 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -1175,8 +1175,8 @@ Item_cond::fix_fields(THD *thd,TABLE_LIST *tables)
   List_iterator<Item> li(list);
   Item *item;
   char buff[sizeof(char*)];			// Max local vars in function
-  used_tables_cache=0;
-  const_item_cache=0;
+  not_null_tables_cache= used_tables_cache= 0;
+  const_item_cache= 0;
   /*
     and_table_cache is the value that Item_cond_or() returns for
     not_null_tables()
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index 5613f1eeb07..f27ba435729 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -3154,7 +3154,7 @@ enum options {
   OPT_MAX_BINLOG_CACHE_SIZE, OPT_MAX_BINLOG_SIZE,
   OPT_MAX_CONNECTIONS, OPT_MAX_CONNECT_ERRORS,
   OPT_MAX_DELAYED_THREADS, OPT_MAX_HEP_TABLE_SIZE,
-  OPT_MAX_JOIN_SIZE, OPT_MAX_SORT_LENGTH,
+  OPT_MAX_JOIN_SIZE, OPT_MAX_SORT_LENGTH, OPT_MAX_SEEKS_FOR_KEY,
   OPT_MAX_TMP_TABLES, OPT_MAX_USER_CONNECTIONS,
   OPT_MAX_WRITE_LOCK_COUNT, OPT_BULK_INSERT_BUFFER_SIZE,
   OPT_MYISAM_BLOCK_SIZE, OPT_MYISAM_MAX_EXTRA_SORT_FILE_SIZE,
@@ -3832,6 +3832,11 @@ replicating a LOAD DATA INFILE command",
    (gptr*) &global_system_variables.max_join_size,
    (gptr*) &max_system_variables.max_join_size, 0, GET_HA_ROWS, REQUIRED_ARG,
    ~0L, 1, ~0L, 0, 1, 0},
+  { "max_seeks_for_key", OPT_MAX_SEEKS_FOR_KEY,
+    "Limit assumed max number of seeks when looking up rows based on a key",
+    (gptr*) &global_system_variables.max_seeks_for_key,
+    (gptr*) &max_system_variables.max_seeks_for_key, 0, GET_ULONG,
+    REQUIRED_ARG, ~0L, 1, ~0L, 0, 1, 0 },
   {"max_sort_length", OPT_MAX_SORT_LENGTH,
    "The number of bytes to use when sorting BLOB or TEXT values (only the first max_sort_length bytes of each value are used; the rest are ignored).",
    (gptr*) &global_system_variables.max_sort_length,
diff --git a/sql/set_var.cc b/sql/set_var.cc
index 32603ec51d9..3edcdbc1f7f 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -154,6 +154,8 @@ sys_var_thd_ulong	sys_max_heap_table_size("max_heap_table_size",
 sys_var_thd_ha_rows	sys_max_join_size("max_join_size",
 					  &SV::max_join_size,
 					  fix_max_join_size);
+sys_var_thd_ulong	sys_max_seeks_for_key("max_seeks_for_key",
+					      &SV::max_seeks_for_key);
 #ifndef TO_BE_DELETED	/* Alias for max_join_size */
 sys_var_thd_ha_rows	sys_sql_max_join_size("sql_max_join_size",
 					      &SV::max_join_size,
@@ -348,6 +350,7 @@ sys_var *sys_variables[]=
   &sys_max_delayed_threads,
   &sys_max_heap_table_size,
   &sys_max_join_size,
+  &sys_max_seeks_for_key,
   &sys_max_sort_length,
   &sys_max_tmp_tables,
   &sys_max_user_connections,
@@ -492,6 +495,7 @@ struct show_var_st init_vars[]= {
   {sys_max_delayed_threads.name,(char*) &sys_max_delayed_threads,   SHOW_SYS},
   {sys_max_heap_table_size.name,(char*) &sys_max_heap_table_size,   SHOW_SYS},
   {sys_max_join_size.name,	(char*) &sys_max_join_size,	    SHOW_SYS},
+  {sys_max_seeks_for_key.name,  (char*) &sys_max_seeks_for_key,	    SHOW_SYS},
   {sys_max_sort_length.name,	(char*) &sys_max_sort_length,	    SHOW_SYS},
   {sys_max_user_connections.name,(char*) &sys_max_user_connections, SHOW_SYS},
   {sys_max_tmp_tables.name,	(char*) &sys_max_tmp_tables,	    SHOW_SYS},
diff --git a/sql/sql_class.h b/sql/sql_class.h
index 3246f77c77a..d1b2ef82ccb 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -310,6 +310,7 @@ struct system_variables
   ulong tx_isolation;
   ulong table_type;
   ulong default_week_format;
+  ulong max_seeks_for_key;
 
   my_bool log_warnings;
   my_bool low_priority_updates;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 67bec77e245..f4c7a2ab031 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -1271,14 +1271,14 @@ make_join_statistics(JOIN *join,TABLE_LIST *tables,COND *conds,
 
     /*
       Set a max range of how many seeks we can expect when using keys
-      This was (s->read_time*5), but this was too low with small rows
+      This is can't be to high as otherwise we are likely to use
+      table scan.
     */
-    s->worst_seeks= (double) s->found_records / 5;
+    s->worst_seeks= min((double) s->found_records / 10,
+			(double) s->read_time*3);
     if (s->worst_seeks < 2.0)			// Fix for small tables
       s->worst_seeks=2.0;
 
-    /* if (s->type == JT_EQ_REF)
-      continue; */
     if (s->const_keys)
     {
       ha_rows records;
@@ -1884,6 +1884,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
       best=best_time=records=DBL_MAX;
       KEYUSE *best_key=0;
       uint best_max_key_part=0;
+      my_bool found_constrain= 0;
 
       if (s->keyuse)
       {						/* Use key if possible */
@@ -1964,6 +1965,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
           }
           else
           {
+	  found_constrain= 1;
 	  /*
 	    Check if we found full key
 	  */
@@ -2000,16 +2002,18 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
 		    records=2.0;		// Can't be as good as a unique
 		}
 	      }
+	      /* Limit the number of matched rows */
+	      tmp= records;
+	      set_if_smaller(tmp, (double) thd->variables.max_seeks_for_key);
 	      if (table->used_keys & ((key_map) 1 << key))
 	      {
 		/* we can use only index tree */
 		uint keys_per_block= table->file->block_size/2/
 		  (keyinfo->key_length+table->file->ref_length)+1;
-		tmp=(record_count*(records+keys_per_block-1)/
-		     keys_per_block);
+		tmp=record_count*(tmp+keys_per_block-1)/keys_per_block;
 	      }
 	      else
-		tmp=record_count*min(records,s->worst_seeks);
+		tmp=record_count*min(tmp,s->worst_seeks);
 	    }
 	  }
 	  else
@@ -2039,7 +2043,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
 		{
 		  /*
 		    Assume that the first key part matches 1% of the file
-		    and that the hole key matches 10 (dupplicates) or 1
+		    and that the hole key matches 10 (duplicates) or 1
 		    (unique) records.
 		    Assume also that more key matches proportionally more
 		    records
@@ -2071,6 +2075,8 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
 		  records=(ulong) tmp;
 		}
 	      }
+	      /* Limit the number of matched rows */
+	      set_if_smaller(tmp, (double) thd->variables.max_seeks_for_key);
 	      if (table->used_keys & ((key_map) 1 << key))
 	      {
 		/* we can use only index tree */
@@ -2113,20 +2119,31 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
 	    s->table->used_keys && best_key) &&
 	  !(s->table->force_index && best_key))
       {						// Check full join
+	ha_rows rnd_records= s->found_records;
 	if (s->on_expr)
 	{
-	  tmp=rows2double(s->found_records);	// Can't use read cache
+	  tmp=rows2double(rnd_records);		// Can't use read cache
 	}
 	else
 	{
 	  tmp=(double) s->read_time;
-	  /* Calculate time to read through cache */
+	  /* Calculate time to read previous rows through cache */
 	  tmp*=(1.0+floor((double) cache_record_length(join,idx)*
 			  record_count /
 			  (double) thd->variables.join_buff_size));
 	}
+
+	/*
+	  If there is a restriction on the table, assume that 25% of the
+	  rows can be skipped on next part.
+	  This is to force tables that this table depends on before this
+	  table
+	*/
+	if (found_constrain)
+	  rnd_records-= rnd_records/4;
+
 	if (best == DBL_MAX ||
-	    (tmp  + record_count/(double) TIME_FOR_COMPARE*s->found_records <
+	    (tmp  + record_count/(double) TIME_FOR_COMPARE*rnd_records <
 	     best + record_count/(double) TIME_FOR_COMPARE*records))
 	{
 	  /*
@@ -2134,7 +2151,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
 	    will ensure that this will be used
 	  */
 	  best=tmp;
-	  records= rows2double(s->found_records);
+	  records= rows2double(rnd_records);
 	  best_key=0;
 	}
       }