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* Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big

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tables
Currently in INSERT ... SELECT ... LIMIT ... the compiler uses a 
temporary table to store the results of SELECT ... LIMIT .. and then
uses that table as a source for INSERT. The problem is that in some cases
it actually skips the LIMIT clause in doing that and materializes the 
whole SELECT result set regardless of the LIMIT.
This fix is limiting the process of filling up the temp table with only 
that much rows that will be actually used by propagating the LIMIT value.


mysql-test/r/insert_select.result:
  * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big
                tables
  - a test demonstrating the code path
mysql-test/t/insert_select.test:
  * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big
                tables
  - a test demonstrating the code path
sql/sql_select.cc:
  * Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big
                tables
  - pass through the real LIMIT number if the temp table is created for
    buffering results.
  - set the counter for all the cases when the temp table is not used for
    grouping
This commit is contained in:
unknown 2006-06-19 13:22:42 +03:00
parent 6297d1ab38
commit 124cb126fa
3 changed files with 25 additions and 4 deletions
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4
mysql-test/r/insert_select.result
View file

@ -686,3 +686,7 @@ ERROR 42S22: Unknown column 'z' in 'field list'
insert into t1(x,y) select x,z from t2 on duplicate key update x=values(t2.x);
ERROR 42S02: Unknown table 't2' in field list
drop table t1,t2;
CREATE TABLE t1 (a int PRIMARY KEY);
INSERT INTO t1 values (1), (2);
INSERT INTO t1 SELECT a + 2 FROM t1 LIMIT 1;
DROP TABLE t1;

13
mysql-test/t/insert_select.test
View file

@ -226,4 +226,17 @@ insert into t1(x,y) select x,z from t2 on duplicate key update x=values(z);
insert into t1(x,y) select x,z from t2 on duplicate key update x=values(t2.x);
drop table t1,t2;
#
# Bug #9676: INSERT INTO x SELECT .. FROM x LIMIT 1; slows down with big
# tables
#
#Note: not an exsaustive test : just a check of the code path.
CREATE TABLE t1 (a int PRIMARY KEY);
INSERT INTO t1 values (1), (2);
INSERT INTO t1 SELECT a + 2 FROM t1 LIMIT 1;
DROP TABLE t1;
# End of 4.1 tests

12
sql/sql_select.cc
View file

@ -888,8 +888,9 @@ JOIN::optimize()
group_list ? 0 : select_distinct,
group_list && simple_group,
select_options,
(order == 0 || skip_sort_order) ? select_limit :
HA_POS_ERROR,
(order == 0 || skip_sort_order ||
test(select_options & OPTION_BUFFER_RESULT)) ?
select_limit : HA_POS_ERROR,
(char *) "")))
DBUG_RETURN(1);
@ -5530,6 +5531,11 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
keyinfo->key_length+= key_part_info->length;
}
}
else
{
set_if_smaller(table->max_rows, rows_limit);
param->end_write_records= rows_limit;
}
if (distinct && field_count != param->hidden_field_count)
{
@ -5544,8 +5550,6 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
null_pack_length-=hidden_null_pack_length;
keyinfo->key_parts= ((field_count-param->hidden_field_count)+
test(null_pack_length));
set_if_smaller(table->max_rows, rows_limit);
param->end_write_records= rows_limit;
table->distinct=1;
table->keys=1;
if (blob_count)