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BUG#20604: FORCE INDEX uses keys disabled by ALTER TABLE

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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.
This commit is contained in:
unknown 2007-01-29 15:07:11 +01:00
parent 4d7994ad68
commit 190efb06e7
5 changed files with 51 additions and 8 deletions
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7
mysql-test/r/key.result
View file

@ -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;

11
mysql-test/t/key.test
View file

@ -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;

7
sql/sql_base.cc
View file

@ -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)
{

11
sql/sql_select.cc
View file

@ -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)
{

23
sql/table.h
View file

@ -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 */