@ -3,7 +3,7 @@
* extended_stats . c
* POSTGRES extended statistics
*
* Generic code supporting statistic objects created via CREATE STATISTICS .
* Generic code supporting statistics objects created via CREATE STATISTICS .
*
*
* Portions Copyright ( c ) 1996 - 2017 , PostgreSQL Global Development Group
@ -35,14 +35,15 @@
/*
* Used internally to refer to an individual pg_statistic_ext entry .
* Used internally to refer to an individual statistics object , i . e . ,
* a pg_statistic_ext entry .
*/
typedef struct StatExtEntry
{
Oid statOid ; /* OID of pg_statistic_ext entry */
char * schema ; /* statistics schema */
char * name ; /* statistics name */
Bitmapset * columns ; /* attribute numbers covered by the statistics */
char * schema ; /* statistics object's schema */
char * name ; /* statistics object's name */
Bitmapset * columns ; /* attribute numbers covered by the object */
List * types ; /* 'char' list of enabled statistic kinds */
} StatExtEntry ;
@ -59,8 +60,8 @@ static void statext_store(Relation pg_stext, Oid relid,
* Compute requested extended stats , using the rows sampled for the plain
* ( single - column ) stats .
*
* This fetches a list of stats from pg_statistic_ext , computes the stats
* and serializes them back into the catalog ( as bytea values ) .
* This fetches a list of stats types from pg_statistic_ext , computes the
* requested stats , and serializes them back into the catalog .
*/
void
BuildRelationExtStatistics ( Relation onerel , double totalrows ,
@ -98,7 +99,7 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
{
ereport ( WARNING ,
( errcode ( ERRCODE_INVALID_OBJECT_DEFINITION ) ,
errmsg ( " extended statistics \" %s.%s \" could not be collected for relation %s.%s " ,
errmsg ( " statistics object \" %s.%s \" could not be computed for relation \" %s.%s \" " ,
stat - > schema , stat - > name ,
get_namespace_name ( onerel - > rd_rel - > relnamespace ) ,
RelationGetRelationName ( onerel ) ) ,
@ -110,7 +111,7 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
Assert ( bms_num_members ( stat - > columns ) > = 2 & &
bms_num_members ( stat - > columns ) < = STATS_MAX_DIMENSIONS ) ;
/* compute statistic of each type */
/* compute statistic of each requested type */
foreach ( lc2 , stat - > types )
{
char t = ( char ) lfirst_int ( lc2 ) ;
@ -160,7 +161,7 @@ statext_is_kind_built(HeapTuple htup, char type)
}
/*
* Return a list ( of StatExtEntry ) of statistics for the given relation .
* Return a list ( of StatExtEntry ) of statistics objects for the given relation .
*/
static List *
fetch_statentries_for_relation ( Relation pg_statext , Oid relid )
@ -171,7 +172,7 @@ fetch_statentries_for_relation(Relation pg_statext, Oid relid)
List * result = NIL ;
/*
* Prepare to scan pg_statistic_ext for entries having ind relid= this
* Prepare to scan pg_statistic_ext for entries having stx relid= this
* rel .
*/
ScanKeyInit ( & skey ,
@ -329,7 +330,7 @@ statext_store(Relation pg_stext, Oid statOid,
/* there should already be a pg_statistic_ext tuple */
oldtup = SearchSysCache1 ( STATEXTOID , ObjectIdGetDatum ( statOid ) ) ;
if ( ! HeapTupleIsValid ( oldtup ) )
elog ( ERROR , " cache lookup failed for extended statistics %u " , statOid ) ;
elog ( ERROR , " cache lookup failed for statistics object %u " , statOid ) ;
/* replace it */
stup = heap_modify_tuple ( oldtup ,
@ -433,7 +434,7 @@ multi_sort_compare_dims(int start, int end,
/*
* has_stats_of_kind
* Check that the list contains statistic of a given kind
* Check whether the list contains statistic of a given kind
*/
bool
has_stats_of_kind ( List * stats , char requiredkind )
@ -458,11 +459,12 @@ has_stats_of_kind(List *stats, char requiredkind)
* there ' s no match .
*
* The current selection criteria is very simple - we choose the statistics
* referencing the most attributes with the least keys .
* object referencing the most of the requested attributes , breaking ties
* in favor of objects with fewer keys overall .
*
* XXX if multiple statistics exists of the same size matching the same number
* of keys , then the statistics which are chosen depend on the order that they
* appear in the stats list . Perhaps this needs to be more definitive .
* XXX if multiple statistics objects tie on both criteria , then which object
* is chosen depends on the order that they appear in the stats list . Perhaps
* further tiebreakers are needed .
*/
StatisticExtInfo *
choose_best_statistics ( List * stats , Bitmapset * attnums , char requiredkind )
@ -479,7 +481,7 @@ choose_best_statistics(List *stats, Bitmapset *attnums, char requiredkind)
int numkeys ;
Bitmapset * matched ;
/* skip statistics that are not the correct type */
/* skip statistics that are not of the correct type */
if ( info - > kind ! = requiredkind )
continue ;
@ -495,9 +497,9 @@ choose_best_statistics(List *stats, Bitmapset *attnums, char requiredkind)
numkeys = bms_num_members ( info - > keys ) ;
/*
* Use these statistics when it increases the number of matched
* clauses or when it matches the same number of attributes but these
* stats have fewer keys than any previous match .
* Use this object when it increases the number of matched clauses or
* when it matches the same number of attributes but these stats hav e
* fewer keys than any previous match .
*/
if ( num_matched > best_num_matched | |
( num_matched = = best_num_matched & & numkeys < best_match_keys ) )
Tom Lane
8 years ago