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WL#3527: Extend IGNORE INDEX so places where index is ignored

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can be specified
Currently MySQL allows one to specify what indexes to ignore during
join optimization. The scope of the current USE/FORCE/IGNORE INDEX 
statement is only the FROM clause, while all other clauses are not 
affected.

However, in certain cases, the optimizer
may incorrectly choose an index for sorting and/or grouping, and
produce an inefficient query plan.

This task provides the means to specify what indexes are
ignored/used for what operation in a more fine-grained manner, thus
making it possible to manually force a better plan. We do this
by extending the current IGNORE/USE/FORCE INDEX syntax to:

IGNORE/USE/FORCE INDEX [FOR {JOIN | ORDER | GROUP BY}]

so that:
- if no FOR is specified, the index hint will apply everywhere.
- if MySQL is started with the compatibility option --old_mode then
  an index hint without a FOR clause works as in 5.0 (i.e, the 
  index will only be ignored for JOINs, but can still be used to
  compute ORDER BY).

See the WL#3527 for further details.
This commit is contained in:
gkodinov/kgeorge@macbook.gmz
2007-03-05 19:08:41 +02:00
parent 6a49f0cd93
commit b9c82eaa89
25 changed files with 727 additions and 458 deletions
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16
sql/sql_update.cc
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@ -130,7 +130,7 @@ int mysql_update(THD *thd,
#endif
uint table_count= 0;
ha_rows updated, found;
key_map old_used_keys;
key_map old_covering_keys;
TABLE *table;
SQL_SELECT *select;
READ_RECORD info;
@ -168,8 +168,8 @@ int mysql_update(THD *thd,
thd->proc_info="init";
table= table_list->table;
/* Calculate "table->used_keys" based on the WHERE */
table->used_keys= table->s->keys_in_use;
/* Calculate "table->covering_keys" based on the WHERE */
table->covering_keys= table->s->keys_in_use;
table->quick_keys.clear_all();
#ifndef NO_EMBEDDED_ACCESS_CHECKS
@ -179,7 +179,7 @@ int mysql_update(THD *thd,
if (mysql_prepare_update(thd, table_list, &conds, order_num, order))
DBUG_RETURN(1);
old_used_keys= table->used_keys; // Keys used in WHERE
old_covering_keys= table->covering_keys; // Keys used in WHERE
/* Check the fields we are going to modify */
#ifndef NO_EMBEDDED_ACCESS_CHECKS
table_list->grant.want_privilege= table->grant.want_privilege= want_privilege;
@ -228,7 +228,7 @@ int mysql_update(THD *thd,
limit= 0; // Impossible WHERE
}
// Don't count on usage of 'only index' when calculating which key to use
table->used_keys.clear_all();
table->covering_keys.clear_all();
#ifdef WITH_PARTITION_STORAGE_ENGINE
if (prune_partitions(thd, table, conds))
@ -303,7 +303,7 @@ int mysql_update(THD *thd,
We can't update table directly; We must first search after all
matching rows before updating the table!
*/
if (used_index < MAX_KEY && old_used_keys.is_set(used_index))
if (used_index < MAX_KEY && old_covering_keys.is_set(used_index))
{
table->key_read=1;
table->mark_columns_used_by_index(used_index);
@ -1091,7 +1091,7 @@ int multi_update::prepare(List<Item> &not_used_values,
}
/*
We have to check values after setup_tables to get used_keys right in
We have to check values after setup_tables to get covering_keys right in
reference tables
*/
@ -1118,7 +1118,7 @@ int multi_update::prepare(List<Item> &not_used_values,
update.link_in_list((byte*) tl, (byte**) &tl->next_local);
tl->shared= table_count++;
table->no_keyread=1;
table->used_keys.clear_all();
table->covering_keys.clear_all();
table->pos_in_table_list= tl;
}
}