From: Jonas Oreland Date: February 23 2011 6:15pm Subject: Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223) Bug#11804277 List-Archive: http://lists.mysql.com/commits/131971 Message-Id: <4D654ED5.20903@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit 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 ( LT/GT>> - A closed bound range ( BETWEEN AND) >>> - A (partial) EQ-range ( EQ) >>> >>> ... 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 >>> ' LT/GT' 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 .. -> 10% selectivity >>> + } >>> + // High range open >>> + else if (!max_key_length) >>> + { >>> + rows= table_rows/10; //..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; //.. -> 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 >>> >>> >>> >>> >>> >> > >