On 23.02.2011 18:00, Jonas Oreland wrote:
> Hi OJ,
>
> 1) What do you think about using heuristic even if we don't have row-count.
> E.g if we don't have row-count, set it to 100 and run you range-heuristic anyway
Yes, would likely be usefull in those cases.
> 2) What do you think about making sure that EQ is preferred over LT even if row-count
> is low,
> so that the divisions don't make estimate the same...if row-count is low...
Yes, could be a good idea. That would be something like:
if (EQ)
return max(E(#rows),2.0);
else
return max(E(#rows),3.0);
Right ?
(if It is a completely specified EQuality on PK or Unique key it is
always preferred as you suggest.
(Fixed by Bug#59517))
Ole John
> /Jonas
>
> On 02/23/11 16:54, Ole John Aske wrote:
>> #At file:///net/fimafeng09/export/home/tmp/oleja/mysql/mysql-5.1-telco-7.0/ based
> on revid:ole.john.aske@stripped
>>
>> 4223 Ole John Aske 2011-02-23
>> Fix for bug#11804277 - INCORRECT INDEX MAY BE SELECTED DUE TO INSUFFICIENT
> STATISTICS FROM CLUSTER
>>
>> Add heuristics to ha_ndbcluster::records_in_range()
>> which identifies a range as:
>>
>> - An open bound range (<column> LT/GT<bound)
>> - A closed bound range (<column> BETWEEN<low>
> AND<HIGH>)
>> - A (partial) EQ-range (<column> EQ<bound>)
>>
>> ... Or a combination of these....
>>
>> These are handled as follows:
>>
>> Open bound ranges
>> -----------------
>> Without a histogram of how the values in the index are
>> distributed, we can only assume an equal distrubution.
>> A statistically correct estimate for a condition of the form
>> '<column> LT/GT<bound>' would then have been to assume it
> selects
>> 50% of the rows in the table. However, I have experienced that
>> this will cause the range-cost to directly compete with the cost
>> of a full table scan. We should therefore be somewhat more
>> conservative and estimate 10% of the rows to be returned.
>>
>> Closed bound range
>> ------------------
>> We assume this to be somewhat better than an open bounded range
>> returning 5% of the rows in the table.
>>
>> EQ-range
>> --------
>> An EQ-range will excatly specify a fraction of the first part of
>> an index. It is reasonable to assume:
>>
>> - Specifing a larger fraction of the index will improve the
>> selectivity of the EQ-range.
>> - Each part of the specified EQ-range will have the same
>> selectivity.
>>
>> We can model this as a Binomial Distribution of the indexed
>> values. http://en.wikipedia.org/wiki/Binomial_distrib
>>
>> modified:
>> mysql-test/suite/ndb/r/ndb_condition_pushdown.result
>> mysql-test/suite/ndb/r/ndb_index.result
>> mysql-test/suite/ndb/r/ndb_index_unique.result
>> mysql-test/suite/ndb/r/ndb_read_multi_range.result
>> mysql-test/suite/ndb/r/ndb_statistics.result
>> mysql-test/suite/ndb/t/ndb_statistics.test
>> sql/ha_ndbcluster.cc
>> === modified file 'mysql-test/suite/ndb/r/ndb_condition_pushdown.result'
>> --- a/mysql-test/suite/ndb/r/ndb_condition_pushdown.result 2011-01-17 13:29:52
> +0000
>> +++ b/mysql-test/suite/ndb/r/ndb_condition_pushdown.result 2011-02-23 15:54:12
> +0000
>> @@ -1910,7 +1910,7 @@ insert into NodeAlias VALUES(null, 8 , '
>> 12:22:26');
>> explain select * from NodeAlias where (aliasKey LIKE '491803%');
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE NodeAlias range NodeAlias_KeyIndex NodeAlias_KeyIndex 48 NULL 10 Using
> where with pushed condition
>> +1 SIMPLE NodeAlias range NodeAlias_KeyIndex NodeAlias_KeyIndex 48 NULL 2 Using
> where with pushed condition
>> select * from NodeAlias where (aliasKey LIKE '491803%') order by id;
>> id nodeId displayName aliasKey objectVersion changed
>> 7 8 491803% 491803% 0 2008-03-10 12:22:26
>> @@ -2225,7 +2225,7 @@ join tx as t2 on tx.a = t2.c and tx.b =
>> where t2.a = 4
>> group by t2.c;
>> id select_type table type possible_keys key key_len ref rows filtered Extra
>> -1 SIMPLE t2 ref PRIMARY PRIMARY 4 const 10 100.00 Using where; Using filesort
>> +1 SIMPLE t2 ref PRIMARY PRIMARY 4 const 2 100.00 Using where; Using filesort
>> 1 SIMPLE tx eq_ref PRIMARY PRIMARY 8 test.t2.c,test.t2.d 1 100.00
>> Warnings:
>> Note 1003 select `test`.`t2`.`c` AS `c`,count(distinct `test`.`t2`.`a`) AS
> `count(distinct t2.a)` from `test`.`tx` join `test`.`tx` `t2` where ((`test`.`tx`.`b` =
> `test`.`t2`.`d`) and (`test`.`tx`.`a` = `test`.`t2`.`c`) and (`test`.`t2`.`a` = 4)) group
> by `test`.`t2`.`c`
>> @@ -2242,7 +2242,7 @@ join tx as t2 on tx.a = t2.c and tx.b =
>> where t2.a = 4
>> group by t2.c;
>> id select_type table type possible_keys key key_len ref rows filtered Extra
>> -1 SIMPLE t2 ref PRIMARY PRIMARY 4 const 10 100.00 Using where; Using filesort
>> +1 SIMPLE t2 ref PRIMARY PRIMARY 4 const 2 100.00 Using where; Using filesort
>> 1 SIMPLE tx eq_ref PRIMARY PRIMARY 8 test.t2.c,test.t2.d 1 100.00
>> Warnings:
>> Note 1003 select `test`.`t2`.`c` AS `c`,count(distinct `test`.`t2`.`a`) AS
> `count(distinct t2.a)` from `test`.`tx` join `test`.`tx` `t2` where ((`test`.`tx`.`b` =
> `test`.`t2`.`d`) and (`test`.`tx`.`a` = `test`.`t2`.`c`) and (`test`.`t2`.`a` = 4)) group
> by `test`.`t2`.`c`
>>
>> === modified file 'mysql-test/suite/ndb/r/ndb_index.result'
>> --- a/mysql-test/suite/ndb/r/ndb_index.result 2010-12-22 11:13:45 +0000
>> +++ b/mysql-test/suite/ndb/r/ndb_index.result 2011-02-23 15:54:12 +0000
>> @@ -306,7 +306,7 @@ explain
>> select i,vc from t1
>> where i>=1 or vc> '0';
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t1 index_merge PRIMARY,i1,i2 i1,i2 5,18 NULL 20 Using
> sort_union(i1,i2); Using where with pushed condition
>> +1 SIMPLE t1 index_merge PRIMARY,i1,i2 i1,i2 5,18 NULL 4 Using sort_union(i1,i2);
> Using where with pushed condition
>> select i,vc from t1
>> where i>=1 or vc> '0';
>> i vc
>> @@ -350,7 +350,7 @@ explain
>> select i,vc from t2
>> where i>=1 or vc> '0';
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t2 index_merge i1,i2 i1,i2 5,19 NULL 20 Using sort_union(i1,i2); Using
> where with pushed condition
>> +1 SIMPLE t2 index_merge i1,i2 i1,i2 5,19 NULL 4 Using sort_union(i1,i2); Using
> where with pushed condition
>> select i,vc from t2
>> where i>=1 or vc> '0';
>> i vc
>>
>> === modified file 'mysql-test/suite/ndb/r/ndb_index_unique.result'
>> --- a/mysql-test/suite/ndb/r/ndb_index_unique.result 2011-01-18 07:49:14 +0000
>> +++ b/mysql-test/suite/ndb/r/ndb_index_unique.result 2011-02-23 15:54:12 +0000
>> @@ -185,7 +185,7 @@ set @old_ecpd = @@session.engine_conditi
>> set engine_condition_pushdown = true;
>> explain select * from t2 where (b = 3 OR b = 5) AND c IS NULL AND a< 9
> order by a;
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t2 range PRIMARY,b b 9 NULL 2 Using where with pushed condition; Using
> filesort
>> +1 SIMPLE t2 range PRIMARY,b PRIMARY 4 NULL 2 Using where with pushed condition
>> select * from t2 where (b = 3 OR b = 5) AND c IS NULL AND a< 9 order by a;
>> a b c
>> 3 3 NULL
>>
>> === modified file 'mysql-test/suite/ndb/r/ndb_read_multi_range.result'
>> --- a/mysql-test/suite/ndb/r/ndb_read_multi_range.result 2011-01-18 07:49:14
> +0000
>> +++ b/mysql-test/suite/ndb/r/ndb_read_multi_range.result 2011-02-23 15:54:12
> +0000
>> @@ -605,7 +605,7 @@ SELECT DISTINCT STRAIGHT_JOIN t1.pk FROM
>> t1 LEFT JOIN t2 ON t2.a = t1.a AND t2.pk != 6;
>> id select_type table type possible_keys key key_len ref rows Extra
>> 1 SIMPLE t1 ALL NULL NULL NULL NULL 3000 Using temporary
>> -1 SIMPLE t2 range PRIMARY PRIMARY 4 NULL 20 Using where; Distinct
>> +1 SIMPLE t2 range PRIMARY PRIMARY 4 NULL 4 Using where; Distinct
>> SELECT DISTINCT STRAIGHT_JOIN t1.pk FROM
>> t1 LEFT JOIN t2 ON t2.a = t1.a AND t2.pk != 6;
>> drop table t1, t2;
>>
>> === modified file 'mysql-test/suite/ndb/r/ndb_statistics.result'
>> --- a/mysql-test/suite/ndb/r/ndb_statistics.result 2011-01-18 11:49:03 +0000
>> +++ b/mysql-test/suite/ndb/r/ndb_statistics.result 2011-02-23 15:54:12 +0000
>> @@ -38,24 +38,124 @@ id select_type table type possible_keys
>> EXPLAIN
>> SELECT * FROM t10000 WHERE k>= 42 and k< 10000;
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 10 Using where with pushed
> condition
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 500 Using where with pushed
> condition
>> EXPLAIN
>> SELECT * FROM t10000 WHERE k BETWEEN 42 AND 10000;
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 10 Using where with pushed
> condition
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 500 Using where with pushed
> condition
>> EXPLAIN
>> SELECT * FROM t10000 WHERE k< 42;
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 10 Using where with pushed
> condition
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 1000 Using where with pushed
> condition
>> EXPLAIN
>> SELECT * FROM t10000 WHERE k> 42;
>> id select_type table type possible_keys key key_len ref rows Extra
>> -1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 10 Using where with pushed
> condition
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 1000 Using where with pushed
> condition
>> EXPLAIN
>> SELECT * FROM t10000 AS X JOIN t10000 AS Y
>> ON Y.I=X.I AND Y.J = X.I;
>> id select_type table type possible_keys key key_len ref rows Extra
>> 1 SIMPLE X ALL I NULL NULL NULL 10000
>> 1 SIMPLE Y ref J,I I 10 test.X.I,test.X.I 11 Using where
>> +EXPLAIN
>> +SELECT * FROM t100 WHERE k< 42;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t100 range PRIMARY PRIMARY 4 NULL 10 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t100 WHERE k> 42;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t100 range PRIMARY PRIMARY 4 NULL 10 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE k< 42;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 1000 Using where with pushed
> condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE k> 42;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 1000 Using where with pushed
> condition
>> +EXPLAIN
>> +SELECT * FROM t100 WHERE k BETWEEN 42 AND 10000;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t100 range PRIMARY PRIMARY 4 NULL 5 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE k BETWEEN 42 AND 10000;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range PRIMARY PRIMARY 4 NULL 500 Using where with pushed
> condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref I I 5 const 200 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref J J 5 const 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J = 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref J,I I 10 const,const 4 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref I I 5 const 200 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J> 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I I 10 NULL 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J< 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I I 10 NULL 50 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J BETWEEN 1 AND 10;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I I 10 NULL 50 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J = 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref J,I I 10 const,const 4 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref J J 5 const 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K> 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range PRIMARY,J J 9 NULL 50 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K< 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range PRIMARY,J J 9 NULL 50 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K BETWEEN 1 AND 10;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range PRIMARY,J J 9 NULL 25 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K = 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after
> reading const tables
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J> 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I I 10 NULL 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I> 0 AND J = 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref J,I J 5 const 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I> 0 AND J> 1;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I J 5 NULL 1000 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J> 1 AND I = 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I I 10 NULL 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 1 AND I> 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 ref J,I J 5 const 100 Using where with pushed condition
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J> 1 AND I> 0;
>> +id select_type table type possible_keys key key_len ref rows Extra
>> +1 SIMPLE t10000 range J,I J 5 NULL 1000 Using where with pushed condition
>> DROP TABLE t10,t100,t10000;
>> End of 5.1 tests
>>
>> === modified file 'mysql-test/suite/ndb/t/ndb_statistics.test'
>> --- a/mysql-test/suite/ndb/t/ndb_statistics.test 2011-01-18 11:49:03 +0000
>> +++ b/mysql-test/suite/ndb/t/ndb_statistics.test 2011-02-23 15:54:12 +0000
>> @@ -62,6 +62,81 @@ EXPLAIN
>> SELECT * FROM t10000 AS X JOIN t10000 AS Y
>> ON Y.I=X.I AND Y.J = X.I;
>>
>> +#
>> +# Improved heurists for ::records_in_range() statistics
>> +#
>> +
>> +# Open bounded range should return 10% of #rows in table
>> +EXPLAIN
>> +SELECT * FROM t100 WHERE k< 42;
>> +EXPLAIN
>> +SELECT * FROM t100 WHERE k> 42;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE k< 42;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE k> 42;
>> +
>> +#Closed bounded range should return 5% of #rows in table
>> +EXPLAIN
>> +SELECT * FROM t100 WHERE k BETWEEN 42 AND 10000;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE k BETWEEN 42 AND 10000;
>> +
>> +#EQ-range selectivity depends on
>> +# - key length specified
>> +# - #rows in table.
>> +# - unique/non-unique index
>> +# - min 2% selectivity
>> +#
>> +# Possibly combined with open/closed ranges as
>> +# above which further improves selectivity
>> +#
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0;
>> +
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J = 0;
>> +
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J> 1;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J< 1;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J BETWEEN 1 AND 10;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J = 1;
>> +
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K> 1;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K< 1;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K BETWEEN 1 AND 10;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 0 AND K = 1;
>> +
>> +## Verify selection of 'best' index
>> +## (The one of index I/J being EQ)
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I = 0 AND J<> 1;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I<> 0 AND J = 1;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE I<> 0 AND J<> 1;
>> +
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J<> 1 AND I = 0;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J = 1 AND I<> 0;
>> +EXPLAIN
>> +SELECT * FROM t10000 WHERE J<> 1 AND I<> 0;
>> +
>>
>> DROP TABLE t10,t100,t10000;
>>
>>
>> === modified file 'sql/ha_ndbcluster.cc'
>> --- a/sql/ha_ndbcluster.cc 2011-02-18 10:19:20 +0000
>> +++ b/sql/ha_ndbcluster.cc 2011-02-23 15:54:12 +0000
>> @@ -11182,7 +11182,87 @@ ha_ndbcluster::records_in_range(uint inx
>> DBUG_RETURN(rows);
>> }
>>
>> - DBUG_RETURN(10); /* Good guess when you don't know anything */
>> + /* Use simple heuristics to estimate fraction
>> + of 'stats.record' returned from range.
>> + */
>> + if (stats.records != 0&& stats.records != HA_POS_ERROR)
>> + {
>> + Uint64 rows;
>> + Uint64 table_rows= stats.records;
>> + size_t min_key_length= (min_key) ? min_key->length : 0;
>> + size_t max_key_length= (max_key) ? max_key->length : 0;
>> +
>> + // Might have an closed/open range bound:
>> + // Low range open
>> + if (!min_key_length)
>> + {
>> + rows= (!max_key_length)
>> + ? table_rows // No range was specified
>> + : table_rows/10; // -oo ..<high range> -> 10%
> selectivity
>> + }
>> + // High range open
>> + else if (!max_key_length)
>> + {
>> + rows= table_rows/10; //<low range>..oo -> 10%
> selectivity
>> + }
>> + else
>> + {
>> + size_t bounds_len= min(min_key_length,max_key_length);
>> + uint eq_bound_len= 0;
>> + uint eq_bound_offs= 0;
>> +
>> + KEY_PART_INFO* key_part= key_info->key_part;
>> + KEY_PART_INFO* end= key_part+key_info->key_parts;
>> + for (; key_part != end; key_part++)
>> + {
>> + uint part_length= key_part->store_length;
>> + if (eq_bound_offs+part_length> bounds_len ||
>> + memcmp(&min_key->key[eq_bound_offs],
>> +&max_key->key[eq_bound_offs],
>> + part_length))
>> + {
>> + break;
>> + }
>> + eq_bound_len+= key_part->length;
>> + eq_bound_offs+= part_length;
>> + }
>> +
>> + if (!eq_bound_len)
>> + {
>> + rows= table_rows/20; //<low range>..<high range>
> -> 5% selectivity
>> + }
>> + else
>> + {
>> + // Has an equality range on a leading part of 'key_length':
>> + // - Null indicator, and HA_KEY_BLOB_LENGTH bytes in
>> + // 'extra_length' are removed from key_fraction calculations.
>> + // - Assume reduced selectivity for non-unique indexes
>> + // by decreasing 'eq_fraction' by 20%
>> + // - Assume equal selectivity for all eq_parts in key.
>> +
>> + double eq_fraction = (double)(eq_bound_len) /
>> + (key_length - key_info->extra_length);
>> + if (idx_type == ORDERED_INDEX) // Non-unique index -> less
> selectivity
>> + eq_fraction/= 1.20;
>> + if (eq_fraction>= 1.0) // Exact match -> 1 row
>> + DBUG_RETURN(1);
>> +
>> + rows = (Uint64)(table_rows / pow(table_rows, eq_fraction));
>> + if (rows> (table_rows/50)) // EQ-range: Max 2% of rows
>> + rows= (table_rows/50);
>> +
>> + if (min_key_length> eq_bound_offs)
>> + rows/= 2;
>> + if (max_key_length> eq_bound_offs)
>> + rows/= 2;
>> + }
>> + }
>> + if (rows< 2) // At least 2 rows as not exact
>> + rows= 2;
>> + DBUG_RETURN(min(rows,table_rows));
>> + }
>> +
>> + DBUG_RETURN(10); /* Poor guess when you don't know anything */
>> }
>>
>> ulonglong ha_ndbcluster::table_flags(void) const
>>
>>
>>
>>
>>
>
