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Implement multivariate n-distinct coefficients

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Add support for explicitly declared statistic objects (CREATE
STATISTICS), allowing collection of statistics on more complex
combinations that individual table columns.  Companion commands DROP
STATISTICS and ALTER STATISTICS ... OWNER TO / SET SCHEMA / RENAME are
added too.  All this DDL has been designed so that more statistic types
can be added later on, such as multivariate most-common-values and
multivariate histograms between columns of a single table, leaving room
for permitting columns on multiple tables, too, as well as expressions.

This commit only adds support for collection of n-distinct coefficient
on user-specified sets of columns in a single table.  This is useful to
estimate number of distinct groups in GROUP BY and DISTINCT clauses;
estimation errors there can cause over-allocation of memory in hashed
aggregates, for instance, so it's a worthwhile problem to solve.  A new
special pseudo-type pg_ndistinct is used.

(num-distinct estimation was deemed sufficiently useful by itself that
this is worthwhile even if no further statistic types are added
immediately; so much so that another version of essentially the same
functionality was submitted by Kyotaro Horiguchi:
https://postgr.es/m/20150828.173334.114731693.horiguchi.kyotaro@lab.ntt.co.jp
though this commit does not use that code.)

Author: Tomas Vondra.  Some code rework by Álvaro.
Reviewed-by: Dean Rasheed, David Rowley, Kyotaro Horiguchi, Jeff Janes,
    Ideriha Takeshi
Discussion: https://postgr.es/m/543AFA15.4080608@fuzzy.cz
    https://postgr.es/m/20170320190220.ixlaueanxegqd5gr@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2017-03-24 14:06:10 -03:00
parent f120b614e0
commit 7b504eb282
77 changed files with 3599 additions and 63 deletions
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64
src/include/statistics/extended_stats_internal.h Normal file
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/*-------------------------------------------------------------------------
*
* extended_stats_internal.h
* POSTGRES extended statistics internal declarations
*
* Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/include/statistics/extended_stats_internal.h
*
*-------------------------------------------------------------------------
*/
#ifndef EXTENDED_STATS_INTERNAL_H
#define EXTENDED_STATS_INTERNAL_H
#include "utils/sortsupport.h"
#include "statistics/statistics.h"
typedef struct
{
Oid eqopr; /* '=' operator for datatype, if any */
Oid eqfunc; /* and associated function */
Oid ltopr; /* '<' operator for datatype, if any */
} StdAnalyzeData;
typedef struct
{
Datum value; /* a data value */
int tupno; /* position index for tuple it came from */
} ScalarItem;
/* multi-sort */
typedef struct MultiSortSupportData
{
int ndims; /* number of dimensions supported by the */
SortSupportData ssup[1]; /* sort support data for each dimension */
} MultiSortSupportData;
typedef MultiSortSupportData *MultiSortSupport;
typedef struct SortItem
{
Datum *values;
bool *isnull;
} SortItem;
extern MVNDistinct *statext_ndistinct_build(double totalrows,
int numrows, HeapTuple *rows,
Bitmapset *attrs, VacAttrStats **stats);
extern bytea *statext_ndistinct_serialize(MVNDistinct *ndistinct);
extern MVNDistinct *statext_ndistinct_deserialize(bytea *data);
extern MultiSortSupport multi_sort_init(int ndims);
extern void multi_sort_add_dimension(MultiSortSupport mss, int sortdim,
Oid oper);
extern int multi_sort_compare(const void *a, const void *b, void *arg);
extern int multi_sort_compare_dim(int dim, const SortItem * a,
const SortItem * b, MultiSortSupport mss);
extern int multi_sort_compare_dims(int start, int end, const SortItem * a,
const SortItem * b, MultiSortSupport mss);
#endif /* EXTENDED_STATS_INTERNAL_H */