On 02/23/11 19:07, Ole John Aske wrote:
> 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.
can you produce a deterministic testcase for this too...i'd be happy...
but i'm also ok with skipping if it's hard
>> 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 ?
yea something like that...with testcase...
>
> (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
ok, so ok to push after suggested changes
(don't know how to set "patch approved" in new bugdb-look-a-like)
Good patch!
/Jonas
>
>
>
>
>
>
>
>> /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
>>>
>>>
>>>
>>>
>>>
>>
>
>
