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Applied Monty corrections to the FULL SCAN

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optimiser bug patch.
This commit is contained in:
kostja@oak.local
2003-09-17 21:52:05 +04:00
parent f13d9312a7
commit 6fba16eabf
3 changed files with 43 additions and 32 deletions
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55
sql/sql_select.cc
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@@ -1898,7 +1898,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
best=best_time=records=DBL_MAX;
KEYUSE *best_key=0;
uint best_max_key_part=0;
my_bool found_constrain= 0;
my_bool found_constraint= 0;
if (s->keyuse)
{ /* Use key if possible */
@@ -1979,7 +1979,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
}
else
{
found_constrain= 1;
found_constraint= 1;
/*
Check if we found full key
*/
@@ -2133,12 +2133,28 @@ 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;
/* Estimate cost of reading table. */
tmp= (double) s->read_time;
tmp= s->table->file->scan_time();
/*
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
*/
if (found_constraint)
rnd_records-= rnd_records/4;
if (s->on_expr) // Can't use join cache
{
/* We have to read the whole table for each record */
tmp*= record_count;
tmp= record_count *
/* We have to read the whole table for each record */
(tmp +
/*
And we have to skip rows which does not satisfy join
condition for each record.
*/
(s->records - rnd_records)/(double) TIME_FOR_COMPARE);
}
else
{
@@ -2146,30 +2162,25 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
tmp*= (1.0 + floor((double) cache_record_length(join,idx) *
record_count /
(double) thd->variables.join_buff_size));
/*
We don't make full cartesian product between rows in the scanned
table and existing records because we skip all rows from the
scanned table, which does not satisfy join condition when
we read the table (see flush_cached_records for details). Here we
take into account cost to read and skip these records.
*/
tmp+= (s->records - rnd_records)/(double) TIME_FOR_COMPARE;
}
/*
We estimate the cost of making full cortesian product between
rows in the scanned table and generated records as
record_count*s->records/TIME_FOR_COMPARE. Taking into account
cost of evaluating WHERE clause for s->found_records is not
necessary because it costs much less than the cost mentioned
above.
We estimate the cost of evaluating WHERE clause for found records
as record_count * rnd_records + TIME_FOR_COMPARE. This cost plus
tmp give us total cost of using TABLE SCAN
*/
if (best == DBL_MAX ||
(tmp + record_count/(double) TIME_FOR_COMPARE*s->records <
(tmp + record_count/(double) TIME_FOR_COMPARE*rnd_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 the table has a range (s->quick is set) make_join_select()
will ensure that this will be used