Fixes for condition pushdown to storage engine based on comments from code review

mysql-test/r/ndb_condition_pushdown.result

 DROP TABLE IF EXISTS t1,t2;
 CREATE TABLE t1 (
 auto int(5) unsigned NOT NULL auto_increment,
-string char(10) default "hello",
-vstring varchar(10) default "hello",
-bin binary(7) default "hello",
-vbin varbinary(7) default "hello",	
+string char(10),
+vstring varchar(10),
+bin binary(7),
+vbin varbinary(7),	
 tiny tinyint(4) DEFAULT '0' NOT NULL ,
 short smallint(6) DEFAULT '1' NOT NULL ,
 medium mediumint(8) DEFAULT '0' NOT NULL,
@@ -233,17 +233,41 @@ auto
 2
 3
 4
+select auto from t1 where 
+string like "b%" and
+vstring like "b%" and
+bin like "b%" and
+vbin like "b%"
+order by auto;
+auto
+2
+select auto from t1 where 
+string not like "b%" and
+vstring not like "b%" and
+bin not like "b%" and
+vbin not like "b%"
+order by auto;
+auto
+1
+3
+4
 select * from t2 where attr3 is null or attr1 > 2 and pk1= 3 order by pk1;
 pk1	attr1	attr2	attr3
 2	2	NULL	NULL
 3	3	3	d
+select * from t2 where attr3 is not null and attr1 > 2 order by pk1;
+pk1	attr1	attr2	attr3
+3	3	3	d
+4	4	4	e
+5	5	5	f
 select * from t3 where attr2 >  9223372036854775803 and attr3 != 3 order by pk1;
 pk1	attr1	attr2	attr3	attr4
 2	2	9223372036854775804	2	c
 4	4	9223372036854775806	4	e
 5	5	9223372036854775807	5	f
-select * from t2,t3 where t2.attr1 > 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
+select * from t2,t3 where t2.attr1 < 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
 pk1	attr1	attr2	attr3	pk1	attr1	attr2	attr3	attr4
+0	0	0	a	0	0	0	0	a
 select * from t4 where attr1 < 5 and attr2 > 9223372036854775803 and attr3 != 3 order by t4.pk1;
 pk1	attr1	attr2	attr3	attr4
 2	2	9223372036854775804	2	c
@@ -257,8 +281,8 @@ set engine_condition_pushdown = on;
 select auto from t1 where 
 string = "aaaa" and 
 vstring = "aaaa" and 
-bin = "aaaa" and 
-vbin = "aaaa" and 
+/* bin = "aaaa" and 
+vbin = "aaaa" and */
 tiny = -1 and 
 short = -1 and 
 medium = -1 and 
@@ -285,8 +309,8 @@ auto
 select auto from t1 where 
 string != "aaaa" and 
 vstring != "aaaa" and 
-bin != "aaaa" and 
-vbin != "aaaa" and 
+/* bin != "aaaa" and 
+vbin != "aaaa" and */
 tiny != -1 and 
 short != -1 and 
 medium != -1 and 
@@ -315,8 +339,8 @@ auto
 select auto from t1 where 
 string > "aaaa" and 
 vstring > "aaaa" and 
-bin > "aaaa" and 
-vbin > "aaaa" and 
+/* bin > "aaaa" and 
+vbin > "aaaa" and */
 tiny < -1 and 
 short < -1 and 
 medium < -1 and 
@@ -345,8 +369,8 @@ auto
 select auto from t1 where 
 string >= "aaaa" and 
 vstring >= "aaaa" and 
-bin >= "aaaa" and 
-vbin >= "aaaa" and 
+/* bin >= "aaaa" and 
+vbin >= "aaaa" and */
 tiny <= -1 and 
 short <= -1 and 
 medium <= -1 and 
@@ -376,8 +400,8 @@ auto
 select auto from t1 where 
 string < "dddd" and 
 vstring < "dddd" and 
-bin < "dddd" and 
-vbin < "dddd" and 
+/* bin < "dddd" and 
+vbin < "dddd" and */
 tiny > -4 and 
 short > -4 and 
 medium > -4 and 
@@ -406,8 +430,8 @@ auto
 select auto from t1 where 
 string <= "dddd" and 
 vstring <= "dddd" and 
-bin <= "dddd" and 
-vbin <= "dddd" and 
+/* bin <= "dddd" and 
+vbin <= "dddd" and */
 tiny >= -4 and 
 short >= -4 and 
 medium >= -4 and 
@@ -438,8 +462,8 @@ create index medium_index on t1(medium);
 select auto from t1 where 
 string = "aaaa" and 
 vstring = "aaaa" and 
-bin = "aaaa" and 
-vbin = "aaaa" and 
+/* bin = "aaaa" and 
+vbin = "aaaa" and */
 tiny = -1 and 
 short = -1 and 
 medium = -1 and 
@@ -466,8 +490,8 @@ auto
 select auto from t1 where 
 string != "aaaa" and 
 vstring != "aaaa" and 
-bin != "aaaa" and 
-vbin != "aaaa" and 
+/* bin != "aaaa" and 
+vbin != "aaaa" and */
 tiny != -1 and 
 short != -1 and 
 medium != -1 and 
@@ -496,8 +520,8 @@ auto
 select auto from t1 where 
 string > "aaaa" and 
 vstring > "aaaa" and 
-bin > "aaaa" and 
-vbin > "aaaa" and 
+/* bin > "aaaa" and 
+vbin > "aaaa" and */
 tiny < -1 and 
 short < -1 and 
 medium < -1 and 
@@ -526,8 +550,8 @@ auto
 select auto from t1 where 
 string >= "aaaa" and 
 vstring >= "aaaa" and 
-bin >= "aaaa" and 
-vbin >= "aaaa" and 
+/* bin >= "aaaa" and 
+vbin >= "aaaa" and */
 tiny <= -1 and 
 short <= -1 and 
 medium <= -1 and 
@@ -557,8 +581,8 @@ auto
 select auto from t1 where 
 string < "dddd" and 
 vstring < "dddd" and 
-bin < "dddd" and 
-vbin < "dddd" and 
+/* bin < "dddd" and 
+vbin < "dddd" and */
 tiny > -4 and 
 short > -4 and 
 medium > -4 and 
@@ -587,8 +611,8 @@ auto
 select auto from t1 where 
 string <= "dddd" and 
 vstring <= "dddd" and 
-bin <= "dddd" and 
-vbin <= "dddd" and 
+/* bin <= "dddd" and 
+vbin <= "dddd" and */
 tiny >= -4 and 
 short >= -4 and 
 medium >= -4 and 
@@ -615,17 +639,41 @@ auto
 2
 3
 4
+select auto from t1 where 
+string like "b%" and
+vstring like "b%" /* and
+bin like "b%" and
+vbin like "b%" */
+order by auto;
+auto
+2
+select auto from t1 where 
+string not like "b%" and
+vstring not like "b%"/* and
+bin not like "b%" and
+vbin not like "b%" */
+order by auto;
+auto
+1
+3
+4
 select * from t2 where attr3 is null or attr1 > 2 and pk1= 3 order by pk1;
 pk1	attr1	attr2	attr3
 2	2	NULL	NULL
 3	3	3	d
+select * from t2 where attr3 is not null and attr1 > 2 order by pk1;
+pk1	attr1	attr2	attr3
+3	3	3	d
+4	4	4	e
+5	5	5	f
 select * from t3 where attr2 >  9223372036854775803 and attr3 != 3 order by pk1;
 pk1	attr1	attr2	attr3	attr4
 2	2	9223372036854775804	2	c
 4	4	9223372036854775806	4	e
 5	5	9223372036854775807	5	f
-select * from t2,t3 where t2.attr1 > 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
+select * from t2,t3 where t2.attr1 < 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
 pk1	attr1	attr2	attr3	pk1	attr1	attr2	attr3	attr4
+0	0	0	a	0	0	0	0	a
 select * from t4 where attr1 < 5 and attr2 > 9223372036854775803 and attr3 != 3 order by t4.pk1;
 pk1	attr1	attr2	attr3	attr4
 2	2	9223372036854775804	2	c
@@ -635,5 +683,15 @@ pk1	attr1	attr2	attr3	attr4	pk1	attr1	attr2	attr3	attr4
 2	2	9223372036854775804	2	c	2	2	9223372036854775804	2	c
 3	3	9223372036854775805	3	d	3	3	9223372036854775805	3	d
 4	4	9223372036854775806	4	e	4	4	9223372036854775806	4	e
+select auto from t1 where string = "aaaa" collate latin1_general_ci order by auto;
+auto
+1
+select * from t2 where (attr1 < 2) = (attr2 < 2) order by pk1;
+pk1	attr1	attr2	attr3
+0	0	0	a
+1	1	1	b
+3	3	3	d
+4	4	4	e
+5	5	5	f
 set engine_condition_pushdown = @old_ecpd;
 DROP TABLE t1,t2,t3,t4;

mysql-test/t/ndb_condition_pushdown.test

@@ -9,10 +9,10 @@ DROP TABLE IF EXISTS t1,t2;
 #
 CREATE TABLE t1 (
   auto int(5) unsigned NOT NULL auto_increment,
-  string char(10) default "hello",
-  vstring varchar(10) default "hello",
-  bin binary(7) default "hello",
-  vbin varbinary(7) default "hello",	
+  string char(10),
+  vstring varchar(10),
+  bin binary(7),
+  vbin varbinary(7),	
   tiny tinyint(4) DEFAULT '0' NOT NULL ,
   short smallint(6) DEFAULT '1' NOT NULL ,
   medium mediumint(8) DEFAULT '0' NOT NULL,
@@ -233,10 +233,26 @@ time_field <= '04:04:04' and
 date_time <= '1904-04-04 04:04:04' 
 order by auto;
 
+# Test LIKE/NOT LIKE
+select auto from t1 where 
+string like "b%" and
+vstring like "b%" and
+bin like "b%" and
+vbin like "b%"
+order by auto;
+
+select auto from t1 where 
+string not like "b%" and
+vstring not like "b%" and
+bin not like "b%" and
+vbin not like "b%"
+order by auto;
+
 # Various tests 
 select * from t2 where attr3 is null or attr1 > 2 and pk1= 3 order by pk1;
+select * from t2 where attr3 is not null and attr1 > 2 order by pk1;
 select * from t3 where attr2 >  9223372036854775803 and attr3 != 3 order by pk1;
-select * from t2,t3 where t2.attr1 > 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
+select * from t2,t3 where t2.attr1 < 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
 select * from t4 where attr1 < 5 and attr2 > 9223372036854775803 and attr3 != 3 order by t4.pk1;
 select * from t3,t4 where t4.attr1 > 1 and t4.attr2 = t3.attr2 and t4.attr3 < 5 order by t4.pk1;
 
@@ -246,8 +262,8 @@ set engine_condition_pushdown = on;
 select auto from t1 where 
 string = "aaaa" and 
 vstring = "aaaa" and 
-bin = "aaaa" and 
-vbin = "aaaa" and 
+/* bin = "aaaa" and 
+vbin = "aaaa" and */
 tiny = -1 and 
 short = -1 and 
 medium = -1 and 
@@ -273,8 +289,8 @@ order by auto;
 select auto from t1 where 
 string != "aaaa" and 
 vstring != "aaaa" and 
-bin != "aaaa" and 
-vbin != "aaaa" and 
+/* bin != "aaaa" and 
+vbin != "aaaa" and */
 tiny != -1 and 
 short != -1 and 
 medium != -1 and 
@@ -300,8 +316,8 @@ order by auto;
 select auto from t1 where 
 string > "aaaa" and 
 vstring > "aaaa" and 
-bin > "aaaa" and 
-vbin > "aaaa" and 
+/* bin > "aaaa" and 
+vbin > "aaaa" and */
 tiny < -1 and 
 short < -1 and 
 medium < -1 and 
@@ -327,8 +343,8 @@ order by auto;
 select auto from t1 where 
 string >= "aaaa" and 
 vstring >= "aaaa" and 
-bin >= "aaaa" and 
-vbin >= "aaaa" and 
+/* bin >= "aaaa" and 
+vbin >= "aaaa" and */
 tiny <= -1 and 
 short <= -1 and 
 medium <= -1 and 
@@ -354,8 +370,8 @@ order by auto;
 select auto from t1 where 
 string < "dddd" and 
 vstring < "dddd" and 
-bin < "dddd" and 
-vbin < "dddd" and 
+/* bin < "dddd" and 
+vbin < "dddd" and */
 tiny > -4 and 
 short > -4 and 
 medium > -4 and 
@@ -381,8 +397,8 @@ order by auto;
 select auto from t1 where 
 string <= "dddd" and 
 vstring <= "dddd" and 
-bin <= "dddd" and 
-vbin <= "dddd" and 
+/* bin <= "dddd" and 
+vbin <= "dddd" and */
 tiny >= -4 and 
 short >= -4 and 
 medium >= -4 and 
@@ -412,8 +428,8 @@ create index medium_index on t1(medium);
 select auto from t1 where 
 string = "aaaa" and 
 vstring = "aaaa" and 
-bin = "aaaa" and 
-vbin = "aaaa" and 
+/* bin = "aaaa" and 
+vbin = "aaaa" and */
 tiny = -1 and 
 short = -1 and 
 medium = -1 and 
@@ -439,8 +455,8 @@ order by auto;
 select auto from t1 where 
 string != "aaaa" and 
 vstring != "aaaa" and 
-bin != "aaaa" and 
-vbin != "aaaa" and 
+/* bin != "aaaa" and 
+vbin != "aaaa" and */
 tiny != -1 and 
 short != -1 and 
 medium != -1 and 
@@ -466,8 +482,8 @@ order by auto;
 select auto from t1 where 
 string > "aaaa" and 
 vstring > "aaaa" and 
-bin > "aaaa" and 
-vbin > "aaaa" and 
+/* bin > "aaaa" and 
+vbin > "aaaa" and */
 tiny < -1 and 
 short < -1 and 
 medium < -1 and 
@@ -493,8 +509,8 @@ order by auto;
 select auto from t1 where 
 string >= "aaaa" and 
 vstring >= "aaaa" and 
-bin >= "aaaa" and 
-vbin >= "aaaa" and 
+/* bin >= "aaaa" and 
+vbin >= "aaaa" and */
 tiny <= -1 and 
 short <= -1 and 
 medium <= -1 and 
@@ -520,8 +536,8 @@ order by auto;
 select auto from t1 where 
 string < "dddd" and 
 vstring < "dddd" and 
-bin < "dddd" and 
-vbin < "dddd" and 
+/* bin < "dddd" and 
+vbin < "dddd" and */
 tiny > -4 and 
 short > -4 and 
 medium > -4 and 
@@ -547,8 +563,8 @@ order by auto;
 select auto from t1 where 
 string <= "dddd" and 
 vstring <= "dddd" and 
-bin <= "dddd" and 
-vbin <= "dddd" and 
+/* bin <= "dddd" and 
+vbin <= "dddd" and */
 tiny >= -4 and 
 short >= -4 and 
 medium >= -4 and 
@@ -571,11 +587,32 @@ time_field <= '04:04:04' and
 date_time <= '1904-04-04 04:04:04' 
 order by auto;
 
+# Test LIKE/NOT LIKE
+select auto from t1 where 
+string like "b%" and
+vstring like "b%" /* and
+bin like "b%" and
+vbin like "b%" */
+order by auto;
+
+select auto from t1 where 
+string not like "b%" and
+vstring not like "b%"/* and
+bin not like "b%" and
+vbin not like "b%" */
+order by auto;
+
 # Various tests 
 select * from t2 where attr3 is null or attr1 > 2 and pk1= 3 order by pk1;
+select * from t2 where attr3 is not null and attr1 > 2 order by pk1;
 select * from t3 where attr2 >  9223372036854775803 and attr3 != 3 order by pk1;
-select * from t2,t3 where t2.attr1 > 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
+select * from t2,t3 where t2.attr1 < 1 and t2.attr2 = t3.attr2 and t3.attr1 < 5 order by t2.pk1;
 select * from t4 where attr1 < 5 and attr2 > 9223372036854775803 and attr3 != 3 order by t4.pk1;
 select * from t3,t4 where t4.attr1 > 1 and t4.attr2 = t3.attr2 and t4.attr3 < 5 order by t4.pk1;
+
+# Some tests that are currently not supported and should not push condition
+select auto from t1 where string = "aaaa" collate latin1_general_ci order by auto;
+select * from t2 where (attr1 < 2) = (attr2 < 2) order by pk1;
+
 set engine_condition_pushdown = @old_ecpd;
 DROP TABLE t1,t2,t3,t4;

sql/ha_ndbcluster.h

@@ -109,10 +109,18 @@ static const negated_function_mapping neg_map[]=
 };
   
 /*
-  This class is used for serialization of the Item tree for
-  condition pushdown. It is stored in a linked list implemented
-  by Ndb_cond class.
- */
+  This class is the construction element for serialization of Item tree 
+  in condition pushdown.
+  An instance of Ndb_Item represents a constant, table field reference,
+  unary or binary comparison predicate, and start/end of AND/OR.
+  Instances of Ndb_Item are stored in a linked list implemented by Ndb_cond
+  class.
+  The order of elements produced by Ndb_cond::next corresponds to
+  depth-first traversal of the Item (i.e. expression) tree in prefix order.
+  AND and OR have arbitrary arity, so the end of AND/OR group is marked with  
+  Ndb_item with type == NDB_END_COND.
+  NOT items represent negated conditions and generate NAND/NOR groups.
+*/
 class Ndb_item {
  public:
   Ndb_item(NDB_ITEM_TYPE item_type) : type(item_type) {};
@@ -134,6 +142,8 @@ class Ndb_item {
       break;
     }
     case(NDB_FUNCTION):
+      value.item= item_value;
+      break;
     case(NDB_END_COND):
       break;
     }
@@ -146,9 +156,11 @@ class Ndb_item {
     field_value->column_no= column_no;
     value.field_value= field_value;
   };
-  Ndb_item(Item_func::Functype func_type) : type(NDB_FUNCTION)
+  Ndb_item(Item_func::Functype func_type, const Item *item_value) 
+    : type(NDB_FUNCTION)
   {
     qualification.function_type= func_type;
+    value.item= item_value;
   };
   ~Ndb_item()
   { 
@@ -179,6 +191,11 @@ class Ndb_item {
 
   int get_field_no() { return value.field_value->column_no; };
 
+  int argument_count() 
+  { 
+    return ((Item_func *) value.item)->argument_count(); 
+  };
+
   const char* get_val() 
   {  
     switch(type) {
@@ -274,7 +291,7 @@ class Ndb_cond_traverse_context
   Ndb_cond_traverse_context(TABLE *tab, void* ndb_tab, Ndb_cond_stack* stack)
     : table(tab), ndb_table(ndb_tab), 
     supported(TRUE), stack_ptr(stack), cond_ptr(NULL),
-    expect_mask(0), expect_field_result_mask(0), skip(0)
+    expect_mask(0), expect_field_result_mask(0), skip(0), collation(NULL)
   {
     if (stack)
       cond_ptr= stack->ndb_cond;
@@ -318,6 +335,17 @@ class Ndb_cond_traverse_context
     expect_field_result_mask= 0;
     expect_field_result(result);
   };
+  void expect_collation(CHARSET_INFO* col)
+  {
+    collation= col;
+  };
+  bool expecting_collation(CHARSET_INFO* col)
+  {
+    bool matching= (!collation) ? true : (collation == col);
+    collation= NULL;
+
+    return matching;
+  };
 
   TABLE* table;
   void* ndb_table;
@@ -327,6 +355,8 @@ class Ndb_cond_traverse_context
   uint expect_mask;
   uint expect_field_result_mask;
   uint skip;
+  CHARSET_INFO* collation;
+
 };
 
 /*
@@ -428,27 +458,40 @@ class ha_ndbcluster: public handler
   /*
     Condition pushdown
   */
-/*
-  Push a condition to ndbcluster storage engine for evaluation 
-  during table   and index scans. The conditions will be stored on a stack
-  for possibly storing several conditions. The stack can be popped
-  by calling cond_pop, handler::extra(HA_EXTRA_RESET) (handler::reset())
-  will clear the stack.
+
+ /*
+   Push condition down to the table handler.
+   SYNOPSIS
+     cond_push()
+     cond   Condition to be pushed. The condition tree must not be
+     modified by the by the caller.
+   RETURN
+     The 'remainder' condition that caller must use to filter out records.
+     NULL means the handler will not return rows that do not match the
+     passed condition.
+   NOTES
+   The pushed conditions form a stack (from which one can remove the
+   last pushed condition using cond_pop).
+   The table handler filters out rows using (pushed_cond1 AND pushed_cond2 
+   AND ... AND pushed_condN)
+   or less restrictive condition, depending on handler's capabilities.
+   
+   handler->extra(HA_EXTRA_RESET) call empties the condition stack.
+   Calls to rnd_init/rnd_end, index_init/index_end etc do not affect the  
+   condition stack.
    The current implementation supports arbitrary AND/OR nested conditions
    with comparisons between columns and constants (including constant
    expressions and function calls) and the following comparison operators:
-  =, !=, >, >=, <, <=, "is null", and "is not null".
-  
-  RETURN
-    NULL The condition was supported and will be evaluated for each 
-    row found during the scan
-    cond The condition was not supported and all rows will be returned from
-         the scan for evaluation (and thus not saved on stack)
-*/
+   =, !=, >, >=, <, <=, like, "not like", "is null", and "is not null". 
+   Negated conditions are supported by NOT which generate NAND/NOR groups.
+ */ 
   const COND *cond_push(const COND *cond);
-/*
+ /*
    Pop the top condition from the condition stack of the handler instance.
-*/
+   SYNOPSIS
+     cond_pop()
+     Pops the top if condition stack, if stack is not empty
+ */
   void cond_pop();
 
   uint8 table_cache_type();
@@ -536,8 +579,7 @@ private:
                                   NdbScanFilter* filter,
                                   bool negated= false);
   int build_scan_filter_group(Ndb_cond* &cond, 
-                              NdbScanFilter* filter,
-                              bool negated= false);
+                              NdbScanFilter* filter);
   int build_scan_filter(Ndb_cond* &cond, NdbScanFilter* filter);
   int generate_scan_filter(Ndb_cond_stack* cond_stack, 
                            NdbScanOperation* op);

sql/handler.h

@@ -451,7 +451,7 @@ public:
   enum {NONE=0, INDEX, RND} inited;
   bool  auto_increment_column_changed;
   bool implicit_emptied;                /* Can be !=0 only if HEAP */
-
+  const COND *pushed_cond;
 
   handler(TABLE *table_arg) :table(table_arg),
     ref(0), data_file_length(0), max_data_file_length(0), index_file_length(0),
@@ -460,7 +460,8 @@ public:
     create_time(0), check_time(0), update_time(0),
     key_used_on_scan(MAX_KEY), active_index(MAX_KEY),
     ref_length(sizeof(my_off_t)), block_size(0),
-    raid_type(0), ft_handler(0), inited(NONE), implicit_emptied(0)
+    raid_type(0), ft_handler(0), inited(NONE), implicit_emptied(0),
+    pushed_cond(NULL)
     {}
   virtual ~handler(void) { /* TODO: DBUG_ASSERT(inited == NONE); */ }
   int ha_open(const char *name, int mode, int test_if_locked);
@@ -724,23 +725,34 @@ public:
    Condition pushdown to storage engines
  */
 
-/*
-  Push a condition to storage engine for evaluation during table
-  and index scans. The conditions should be stored on a stack
-  for possibly storing several conditions. The stack can be popped
-  by calling cond_pop, handler::extra(HA_EXTRA_RESET) (handler::reset())
-  should clear the stack.
-  The condition can be traversed using Item::traverse_cond
+ /*
+   Push condition down to the table handler.
+   SYNOPSIS
+     cond_push()
+     cond   Condition to be pushed. The condition tree must not be            
+     modified by the by the caller.
    RETURN
-    NULL The condition was supported by the handler and will be evaluated
-         for each row found during the scan
-    cond The condition was not supported and all rows will be returned from
-         the scan for evaluation (and thus not saved on stack)
-*/
+     The 'remainder' condition that caller must use to filter out records.
+     NULL means the handler will not return rows that do not match the
+     passed condition.
+   NOTES
+   The pushed conditions form a stack (from which one can remove the
+   last pushed condition using cond_pop).
+   The table handler filters out rows using (pushed_cond1 AND pushed_cond2 
+   AND ... AND pushed_condN)
+   or less restrictive condition, depending on handler's capabilities.
+   
+   handler->extra(HA_EXTRA_RESET) call empties the condition stack.
+   Calls to rnd_init/rnd_end, index_init/index_end etc do not affect the
+   condition stack.
+ */ 
  virtual const COND *cond_push(const COND *cond) { return cond; };
-/*
+ /*
    Pop the top condition from the condition stack of the handler instance.
-*/
+   SYNOPSIS
+     cond_pop()
+     Pops the top if condition stack, if stack is not empty
+ */
  virtual void cond_pop() { return; };
 };
 

sql/sql_select.cc

@@ -5305,7 +5305,12 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
             DBUG_RETURN(1);
           tab->select_cond=sel->cond=tmp;
 	  if (current_thd->variables.engine_condition_pushdown)
-	    tab->table->file->cond_push(tmp); // Push condition to handler
+          {
+            tab->table->file->pushed_cond= NULL;
+	    /* Push condition to handler */
+            if (!tab->table->file->cond_push(tmp))
+              tab->table->file->pushed_cond= tmp;
+          }
         }
         else
           tab->select_cond= sel->cond= NULL;
@@ -5428,8 +5433,12 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	      tab->cache.select->cond=tmp;
 	      tab->cache.select->read_tables=join->const_table_map;
 	      if (current_thd->variables.engine_condition_pushdown &&
-		  (tmp != tab->select_cond))
-		tab->table->file->cond_push(tmp); // Push condition to handler
+		  (!tab->table->file->pushed_cond))
+              {
+		/* Push condition to handler */
+		if (!tab->table->file->cond_push(tmp))
+                  tab->table->file->pushed_cond= tmp;
+              }
 	    }
 	  }
 	}