database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-12-24 11:21:21 +03:00
Code Activity

Fixed bug mdev-585 (LP bug #637962)

Browse Source 
If, when executing a query with ORDER BY col LIMIT n, the optimizer chose
an index-merge scan to access the table containing col while there existed
an index defined over col then optimizer did not consider the possibility
of using an alternative range scan by this index to avoid filesort. This
could cause a performance degradation if the optimizer flag index_merge was
set up to 'on'.
This commit is contained in:
Igor Babaev
2012-11-01 14:54:33 -07:00
parent 9b6fe96503
commit 7714739b2d
4 changed files with 356 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
sql/sql_select.cc
View File

@@ -18079,15 +18079,18 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit_arg,
*/
if (quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE ||
quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT ||
quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT ||
quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION ||
quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT)
goto use_filesort;
ref_key= select->quick->index;
ref_key_parts= select->quick->used_key_parts;
ref_key= MAX_KEY;
else
{
ref_key= select->quick->index;
ref_key_parts= select->quick->used_key_parts;
}
}
if (ref_key >= 0)
if (ref_key >= 0 && ref_key != MAX_KEY)
{
/*
We come here when there is a REF key.
@@ -18229,7 +18232,8 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit_arg,
else
keys= usable_keys;
if (ref_key >= 0 && table->covering_keys.is_set(ref_key))
if (ref_key >= 0 && ref_key != MAX_KEY &&
table->covering_keys.is_set(ref_key))
ref_key_quick_rows= table->quick_rows[ref_key];
read_time= join->best_positions[tablenr].read_time;