Commit 8d9ffc6a authored by unknown's avatar unknown
Browse files

BUG#16166, "Can't use index_merge with FORCE INDEX": adjust the heurstics check to take into 

account that "FORCE INDEX" disables full table scans, and not range/index_merge scans.
(with post-review fixes)


mysql-test/r/index_merge.result:
  Testcase for BUG#16166
mysql-test/t/index_merge.test:
  Testcase for BUG#16166
sql/sql_select.cc:
  BUG#16166: "Can't use index_merge with FORCE INDEX": adjust the heuristics check:
  if (force-index-is-used && there-is-possible-ref-access && 
  +    THERE IS NO POSSIBLE RANGE/INDEX_MERGE ACCESS)
  {
    ...
parent cdf2eb4b

mysql-test/r/index_merge.result

+18 −0
Original line number Diff line number Diff line
@@ -384,3 +384,21 @@ max(A.key1 + B.key1 + A.key2 + B.key2 + A.key3 + B.key3 + A.key4 + B.key4 + A.ke 
8186

set join_buffer_size= @save_join_buffer_size;

drop table t0, t1, t2, t3, t4;

CREATE TABLE t1 (

cola char(3) not null, colb char(3) not null,  filler char(200),

key(cola), key(colb)

);

INSERT INTO t1 VALUES ('foo','bar', 'ZZ'),('fuz','baz', 'ZZ');

OPTIMIZE TABLE t1;

Table	Op	Msg_type	Msg_text

test.t1	optimize	status	OK

select count(*) from t1;

count(*)

8704

explain select * from t1 WHERE cola = 'foo' AND colb = 'bar';

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	index_merge	cola,colb	cola,colb	3,3	NULL	24	Using intersect(cola,colb); Using where

explain select * from t1 force index(cola,colb) WHERE cola = 'foo' AND colb = 'bar';

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	index_merge	cola,colb	cola,colb	3,3	NULL	24	Using intersect(cola,colb); Using where

drop table t1;

mysql-test/t/index_merge.test

+30 −0
Original line number Diff line number Diff line
@@ -327,3 +327,33 @@ set join_buffer_size= @save_join_buffer_size; 


drop table t0, t1, t2, t3, t4;



# BUG#16166

CREATE TABLE t1 (

  cola char(3) not null, colb char(3) not null,  filler char(200),

  key(cola), key(colb)

);

INSERT INTO t1 VALUES ('foo','bar', 'ZZ'),('fuz','baz', 'ZZ');



--disable_query_log

let $1=9;

while ($1)

{

  eval INSERT INTO t1 SELECT * from t1 WHERE cola = 'foo';

  dec $1;

}



let $1=13;

while ($1)

{

  eval INSERT INTO t1 SELECT * from t1 WHERE cola <> 'foo';

  dec $1;

}



--enable_query_log



OPTIMIZE TABLE t1;

select count(*) from t1;

explain select * from t1 WHERE cola = 'foo' AND colb = 'bar';

explain select * from t1 force index(cola,colb) WHERE cola = 'foo' AND colb = 'bar';

drop table t1;

sql/sql_select.cc

+28 −7
Original line number Diff line number Diff line
@@ -3471,13 +3471,32 @@ best_access_path(JOIN *join, 
    parts of the row from any of the used index.

    This is because table scans uses index and we would not win

    anything by using a table scan.

  */

  if ((records >= s->found_records || best > s->read_time) &&

      !(s->quick && best_key && s->quick->index == best_key->key &&

        best_max_key_part >= s->table->quick_key_parts[best_key->key]) &&

      !((s->table->file->table_flags() & HA_TABLE_SCAN_ON_INDEX) &&

        ! s->table->used_keys.is_clear_all() && best_key) &&

      !(s->table->force_index && best_key))



    A word for word translation of the below if-statement in psergey's

    understanding: we check if we should use table scan if:

    (1) The found 'ref' access produces more records than a table scan

        (or index scan, or quick select), or 'ref' is more expensive than

        any of them.

    (2) This doesn't hold: the best way to perform table scan is to to perform

        'range' access using index IDX, and the best way to perform 'ref' 

        access is to use the same index IDX, with the same or more key parts.

        (note: it is not clear how this rule is/should be extended to 

        index_merge quick selects)

    (3) See above note about InnoDB.

    (4) NOT ("FORCE INDEX(...)" is used for table and there is 'ref' access

             path, but there is no quick select)

        If the condition in the above brackets holds, then the only possible

        "table scan" access method is ALL/index (there is no quick select).

        Since we have a 'ref' access path, and FORCE INDEX instructs us to

        choose it over ALL/index, there is no need to consider a full table

        scan.

  */

  if ((records >= s->found_records || best > s->read_time) &&            // (1)

      !(s->quick && best_key && s->quick->index == best_key->key &&      // (2)

        best_max_key_part >= s->table->quick_key_parts[best_key->key]) &&// (2)

      !((s->table->file->table_flags() & HA_TABLE_SCAN_ON_INDEX) &&      // (3)

        ! s->table->used_keys.is_clear_all() && best_key) &&             // (3)

      !(s->table->force_index && best_key && !s->quick))                 // (4)

  {                                             // Check full join

    ha_rows rnd_records= s->found_records;

    /*
@@ -4460,13 +4479,15 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count, 
	parts of the row from any of the used index.

	This is because table scans uses index and we would not win

	anything by using a table scan.

        (see comment in best_access_path() for more details on the below

         condition)

      */

      if ((records >= s->found_records || best > s->read_time) &&

	  !(s->quick && best_key && s->quick->index == best_key->key &&

	    best_max_key_part >= s->table->quick_key_parts[best_key->key]) &&

	  !((s->table->file->table_flags() & HA_TABLE_SCAN_ON_INDEX) &&

	    ! s->table->used_keys.is_clear_all() && best_key) &&

	  !(s->table->force_index && best_key))

	  !(s->table->force_index && best_key & !s->quick))

      {						// Check full join

        ha_rows rnd_records= s->found_records;

        /*