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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
sql/sql_base.cc
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@ -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)
{