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Fixed bug in the optimiser for FULL TABLE SCAN case:

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to estimate correctly cost of full table scan we should take into
account rows read and skipped on each iteration.


mysql-test/r/distinct.result:
  Fixed test suite: now full scan is used
  less often
mysql-test/r/join_outer.result:
  Fixed test suite: now full scan is used
  less often
mysql-test/r/select_safe.result:
  Fixed test suite: now full scan is used
  less often
This commit is contained in:
unknown
2003-09-15 22:21:39 +04:00
parent cdbc2fe43a
commit db03c7e89f
4 changed files with 27 additions and 29 deletions
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6
mysql-test/r/distinct.result
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@ -173,9 +173,9 @@ INSERT INTO t2 values (1),(2),(3);
INSERT INTO t3 VALUES (1,'1'),(2,'2'),(1,'1'),(2,'2');
explain SELECT distinct t3.a FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;
table type possible_keys key key_len ref rows Extra
t3 index a a 5 NULL 6 Using index; Using temporary
t2 index a a 4 NULL 5 Using index; Distinct
t1 eq_ref PRIMARY PRIMARY 4 t2.a 1 Using where; Distinct
t2 index a a 4 NULL 5 Using index; Using temporary
t1 eq_ref PRIMARY PRIMARY 4 t2.a 1
t3 index a a 5 NULL 5 Using where; Using index
SELECT distinct t3.a FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;
a
1

2
mysql-test/r/join_outer.result
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@ -615,7 +615,7 @@ INSERT INTO t2 VALUES (1,1);
explain SELECT * from t1 left join t2 on t1.id=t2.id where t2.id IS NULL;
table type possible_keys key key_len ref rows Extra
t1 ALL NULL NULL NULL NULL 2
t2 index id id 8 NULL 1 Using where; Using index; Not exists
t2 ref id id 4 t1.id 1 Using where; Using index; Not exists
SELECT * from t1 left join t2 on t1.id=t2.id where t2.id IS NULL;
id name id idx
2 no NULL NULL

2
mysql-test/r/select_safe.result
View File

@ -70,7 +70,7 @@ insert into t1 values (null,"a"),(null,"a"),(null,"a"),(null,"a"),(null,"a"),(nu
explain select STRAIGHT_JOIN * from t1,t1 as t2 where t1.b=t2.b;
table type possible_keys key key_len ref rows Extra
t1 ALL b NULL NULL NULL 21
t2 ALL b NULL NULL NULL 16 Using where
t2 ref b b 21 t1.b 6 Using where
set MAX_SEEKS_FOR_KEY=1;
explain select STRAIGHT_JOIN * from t1,t1 as t2 where t1.b=t2.b;
table type possible_keys key key_len ref rows Extra

30
sql/sql_select.cc
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@ -2133,33 +2133,31 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
s->table->used_keys && best_key) &&
!(s->table->force_index && best_key))
{ // Check full join
ha_rows rnd_records= s->found_records;
if (s->on_expr)
{
tmp=rows2double(rnd_records); // Can't use read cache
}
else
{
/*
Estimate cost of reading table. Note, that we don't read a table
on each iteration as in most cases join buffer is in use.
*/
tmp= (double) s->read_time;
/* Calculate time to read previous rows through cache */
tmp*=(1.0+floor((double) cache_record_length(join,idx)*
record_count /
(double) thd->variables.join_buff_size));
}
/*
In case of full scan we check every row in the table:
here we take into account rows read and skipped, as well as rows
passed to next select
*/
if (best == DBL_MAX ||
(tmp + record_count/(double) TIME_FOR_COMPARE*s->records <
best + record_count/(double) TIME_FOR_COMPARE*records))
{
/*
If there is a restriction on the table, assume that 25% of the
rows can be skipped on next part.
This is to force tables that this table depends on before this
table
*/
ha_rows rnd_records= s->found_records;
if (found_constrain)
rnd_records-= rnd_records/4;
if (best == DBL_MAX ||
(tmp + record_count/(double) TIME_FOR_COMPARE*rnd_records <
best + record_count/(double) TIME_FOR_COMPARE*records))
{
/*
If the table has a range (s->quick is set) make_join_select()
will ensure that this will be used