@ -62,6 +62,7 @@ typedef struct StatExtEntry
char * name ; /* statistics object's name */
Bitmapset * columns ; /* attribute numbers covered by the object */
List * types ; /* 'char' list of enabled statistic kinds */
int stattarget ; /* statistics target (-1 for default) */
} StatExtEntry ;
@ -71,7 +72,8 @@ static VacAttrStats **lookup_var_attr_stats(Relation rel, Bitmapset *attrs,
static void statext_store ( Oid relid ,
MVNDistinct * ndistinct , MVDependencies * dependencies ,
MCVList * mcv , VacAttrStats * * stats ) ;
static int statext_compute_stattarget ( int stattarget ,
int natts , VacAttrStats * * stats ) ;
/*
* Compute requested extended stats , using the rows sampled for the plain
@ -107,6 +109,7 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
MCVList * mcv = NULL ;
VacAttrStats * * stats ;
ListCell * lc2 ;
int stattarget ;
/*
* Check if we can build these stats based on the column analyzed . If
@ -131,6 +134,19 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
Assert ( bms_num_members ( stat - > columns ) > = 2 & &
bms_num_members ( stat - > columns ) < = STATS_MAX_DIMENSIONS ) ;
/* compute statistics target for this statistics */
stattarget = statext_compute_stattarget ( stat - > stattarget ,
bms_num_members ( stat - > columns ) ,
stats ) ;
/*
* Don ' t rebuild statistics objects with statistics target set to 0 ( we
* just leave the existing values around , just like we do for regular
* per - column statistics ) .
*/
if ( stattarget = = 0 )
continue ;
/* compute statistic of each requested type */
foreach ( lc2 , stat - > types )
{
@ -144,7 +160,7 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
stat - > columns , stats ) ;
else if ( t = = STATS_EXT_MCV )
mcv = statext_mcv_build ( numrows , rows , stat - > columns , stats ,
totalrows ) ;
totalrows , stattarget ) ;
}
/* store the statistics in the catalog */
@ -157,6 +173,135 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
MemoryContextDelete ( cxt ) ;
}
/*
* ComputeExtStatisticsRows
* Compute number of rows required by extended statistics on a table .
*
* Computes number of rows we need to sample to build extended statistics on a
* table . This only looks at statistics we can actually build - for example
* when analyzing only some of the columns , this will skip statistics objects
* that would require additional columns .
*
* See statext_compute_stattarget for details about how we compute statistics
* target for a statistics objects ( from the object target , attribute targets
* and default statistics target ) .
*/
int
ComputeExtStatisticsRows ( Relation onerel ,
int natts , VacAttrStats * * vacattrstats )
{
Relation pg_stext ;
ListCell * lc ;
List * lstats ;
MemoryContext cxt ;
MemoryContext oldcxt ;
int result = 0 ;
cxt = AllocSetContextCreate ( CurrentMemoryContext ,
" ComputeExtStatisticsRows " ,
ALLOCSET_DEFAULT_SIZES ) ;
oldcxt = MemoryContextSwitchTo ( cxt ) ;
pg_stext = table_open ( StatisticExtRelationId , RowExclusiveLock ) ;
lstats = fetch_statentries_for_relation ( pg_stext , RelationGetRelid ( onerel ) ) ;
foreach ( lc , lstats )
{
StatExtEntry * stat = ( StatExtEntry * ) lfirst ( lc ) ;
int stattarget = stat - > stattarget ;
VacAttrStats * * stats ;
int nattrs = bms_num_members ( stat - > columns ) ;
/*
* Check if we can build this statistics object based on the columns
* analyzed . If not , ignore it ( don ' t report anything , we ' ll do that
* during the actual build BuildRelationExtStatistics ) .
*/
stats = lookup_var_attr_stats ( onerel , stat - > columns ,
natts , vacattrstats ) ;
if ( ! stats )
continue ;
/*
* Compute statistics target , based on what ' s set for the statistic
* object itself , and for its attributes .
*/
stattarget = statext_compute_stattarget ( stat - > stattarget ,
nattrs , stats ) ;
/* Use the largest value for all statistics objects. */
if ( stattarget > result )
result = stattarget ;
}
table_close ( pg_stext , RowExclusiveLock ) ;
MemoryContextSwitchTo ( oldcxt ) ;
MemoryContextDelete ( cxt ) ;
/* compute sample size based on the statistics target */
return ( 300 * result ) ;
}
/*
* statext_compute_stattarget
* compute statistics target for an extended statistic
*
* When computing target for extended statistics objects , we consider three
* places where the target may be set - the statistics object itself ,
* attributes the statistics is defined on , and then the default statistics
* target .
*
* First we look at what ' s set for the statistics object itself , using the
* ALTER STATISTICS . . . SET STATISTICS command . If we find a valid value
* there ( i . e . not - 1 ) we ' re done . Otherwise we look at targets set for any
* of the attributes the statistic is defined on , and if there are columns
* with defined target , we use the maximum value . We do this mostly for
* backwards compatibility , because this is what we did before having
* statistics target for extended statistics .
*
* And finally , if we still don ' t have a statistics target , we use the value
* set in default_statistics_target .
*/
static int
statext_compute_stattarget ( int stattarget , int nattrs , VacAttrStats * * stats )
{
int i ;
/*
* If there ' s statistics target set for the statistics object , use it .
* It may be set to 0 which disables building of that statistic .
*/
if ( stattarget > = 0 )
return stattarget ;
/*
* The target for the statistics object is set to - 1 , in which case we
* look at the maximum target set for any of the attributes the object
* is defined on .
*/
for ( i = 0 ; i < nattrs ; i + + )
{
/* keep the maximmum statistics target */
if ( stats [ i ] - > attr - > attstattarget > stattarget )
stattarget = stats [ i ] - > attr - > attstattarget ;
}
/*
* If the value is still negative ( so neither the statistics object nor
* any of the columns have custom statistics target set ) , use the global
* default target .
*/
if ( stattarget < 0 )
stattarget = default_statistics_target ;
/* As this point we should have a valid statistics target. */
Assert ( ( stattarget > = 0 ) & & ( stattarget < = 10000 ) ) ;
return stattarget ;
}
/*
* statext_is_kind_built
* Is this stat kind built in the given pg_statistic_ext_data tuple ?
@ -225,6 +370,7 @@ fetch_statentries_for_relation(Relation pg_statext, Oid relid)
entry - > statOid = staForm - > oid ;
entry - > schema = get_namespace_name ( staForm - > stxnamespace ) ;
entry - > name = pstrdup ( NameStr ( staForm - > stxname ) ) ;
entry - > stattarget = staForm - > stxstattarget ;
for ( i = 0 ; i < staForm - > stxkeys . dim1 ; i + + )
{
entry - > columns = bms_add_member ( entry - > columns ,
Tomas Vondra
6 years ago