Commit 190efb06 authored by unknown's avatar unknown
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BUG#20604: FORCE INDEX uses keys disabled by ALTER TABLE 

 
The function that checks whether we can use keys for aggregates,
find_key_for_maxmin(), assumes that keys disabled by ALTER TABLE
... DISABLE KEYS are not in the set table->keys_in_use_for_query.
I.E., if a key is in this set, the optimizer assumes it is free to 
use it.
  
The bug is that keys disabled with ALTER TABLE ... DISABLE KEYS still
appear in table->keys_in_use_for_query When the TABLE object has been 
initialized with setup_tables(). Before setup_tables is called, however, 
keys that are disabled in the aforementioned way are not included in
TABLE::keys_in_use_for_query. 
  
The provided patch changes the code that updates keys_is_use_for_query so 
that it assumes that keys_is_use_for_query already takes into account all 
disabled keys, and generally all keys that should be used by the query.


mysql-test/r/key.result:
  Test for BUG#20604.
  The important part of the test is the explain output that 
  tests what indexes are used.
mysql-test/t/key.test:
  The minimal test case that reveals the bug. The optimizer for 
  aggregates relies on keys disabled with ALTER TABLE ... DISABLE KEYS
  not being in the set TABLE::keys_in_use_for_query. 
  When the execution engine tries to use a disabled index, MyISAM 
  returns an error.
sql/sql_base.cc:
  Exclude the keys disabled by ALTER TABLE ... DISABLE_KEYS 
  from TABLE::keys_in_use_for_query, and in general, don't 
  introduce any new keys. We may not know why keys have been 
  removed at previous stages.
sql/sql_select.cc:
  The intersection operation between table->s->keys_in_use and 
  table->keys_in_use_for_query is no longer necessary. 
  We can trust that the latter is a subset of the former.
sql/table.h:
  Added comments to TABLE_SHARE::keys_in_use and 
  TABLE::keys_in_use_for_query.
parent 4d7994ad

mysql-test/r/key.result

+7 −0
Original line number Diff line number Diff line
@@ -482,3 +482,10 @@ alter table t1 drop index i3, drop index i2, drop index i1; 
alter table t1 add index i3 (c3), add index i2 (c2), add unique index i1 (c1);

ERROR 23000: Duplicate entry '1' for key 'i1'

drop table t1;

CREATE TABLE t1( a TINYINT, KEY(a) ) ENGINE=MyISAM;

INSERT INTO t1 VALUES( 1 );

ALTER TABLE t1 DISABLE KEYS;

EXPLAIN SELECT MAX(a) FROM t1 FORCE INDEX(a);

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	

drop table t1;

mysql-test/t/key.test

+11 −0
Original line number Diff line number Diff line
@@ -442,3 +442,14 @@ alter table t1 drop index i3, drop index i2, drop index i1; 
alter table t1 add index i3 (c3), add index i2 (c2), add unique index i1 (c1);

drop table t1;





#

# Bug #20604: Test for disabled keys with aggregate functions and FORCE INDEX.

#



CREATE TABLE t1( a TINYINT, KEY(a) ) ENGINE=MyISAM;

INSERT INTO t1 VALUES( 1 );

ALTER TABLE t1 DISABLE KEYS;

EXPLAIN SELECT MAX(a) FROM t1 FORCE INDEX(a);



drop table t1;

sql/sql_base.cc

+6 −1
Original line number Diff line number Diff line
@@ -5462,7 +5462,12 @@ bool setup_tables(THD *thd, Name_resolution_context *context, 
      get_key_map_from_key_list(&map, table, table_list->use_index);

      if (map.is_set_all())

	DBUG_RETURN(1);

      table->keys_in_use_for_query=map;

      /* 

	 Don't introduce keys in keys_in_use_for_query that weren't there 

	 before. FORCE/USE INDEX should not add keys, it should only remove

	 all keys except the key(s) specified in the hint.

      */

      table->keys_in_use_for_query.intersect(map);

    }

    if (table_list->ignore_index)

    {

sql/sql_select.cc

+6 −5
Original line number Diff line number Diff line
@@ -12262,13 +12262,14 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit, 
  DBUG_ENTER("test_if_skip_sort_order");

  LINT_INIT(ref_key_parts);



  /* Check which keys can be used to resolve ORDER BY. */

  usable_keys= table->keys_in_use_for_query;



  /*

    Check which keys can be used to resolve ORDER BY.

    We must not try to use disabled keys.

    Keys disabled by ALTER TABLE ... DISABLE KEYS should have already

    been taken into account.

  */

  usable_keys= table->s->keys_in_use;

  /* we must not consider keys that are disabled by IGNORE INDEX */

  usable_keys.intersect(table->keys_in_use_for_query);

  DBUG_ASSERT(usable_keys.is_subset(table->s->keys_in_use));



  for (ORDER *tmp_order=order; tmp_order ; tmp_order=tmp_order->next)

  {

sql/table.h

+21 −2
Original line number Diff line number Diff line
@@ -158,7 +158,12 @@ typedef struct st_table_share 
  LEX_STRING path;                	/* Path to .frm file (from datadir) */

  LEX_STRING normalized_path;		/* unpack_filename(path) */

  LEX_STRING connect_string;

  key_map keys_in_use;                  /* Keys in use for table */



  /* 

     Set of keys in use, implemented as a Bitmap.

     Excludes keys disabled by ALTER TABLE ... DISABLE KEYS.

  */

  key_map keys_in_use;

  key_map keys_for_keyread;

  ha_rows min_rows, max_rows;		/* create information */

  ulong   avg_row_length;		/* create information */
@@ -313,7 +318,21 @@ struct st_table { 
  byte *write_row_record;		/* Used as optimisation in

					   THD::write_row */

  byte *insert_values;                  /* used by INSERT ... UPDATE */

  key_map quick_keys, used_keys, keys_in_use_for_query, merge_keys;

  key_map quick_keys, used_keys;



  /*

    A set of keys that can be used in the query that references this

    table 



    All indexes disabled on the table's TABLE_SHARE (see TABLE::s) will be 

    subtracted from this set upon instantiation. Thus for any TABLE t it holds

    that t.keys_in_use_for_query is a subset of t.s.keys_in_use. Generally we 

    must not introduce any new keys here (see setup_tables).



    The set is implemented as a bitmap.

  */

  key_map keys_in_use_for_query;

  key_map merge_keys;

  KEY  *key_info;			/* data of keys in database */



  Field *next_number_field;		/* Set if next_number is activated */