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/*-------------------------------------------------------------------------
*
* pg_statistic.h
* definition of the system "statistic" relation (pg_statistic)
* along with the relation's initial contents.
*
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/catalog/pg_statistic.h
*
* NOTES
* the genbki.pl script reads this file and generates .bki
* information from the DATA() statements.
*
*-------------------------------------------------------------------------
*/
#ifndef PG_STATISTIC_H
#define PG_STATISTIC_H
#include "catalog/genbki.h"
/* ----------------
* pg_statistic definition. cpp turns this into
* typedef struct FormData_pg_statistic
* ----------------
*/
#define StatisticRelationId 2619
CATALOG(pg_statistic,2619) BKI_WITHOUT_OIDS
{
/* These fields form the unique key for the entry: */
Oid starelid; /* relation containing attribute */
int16 staattnum; /* attribute (column) stats are for */
bool stainherit; /* true if inheritance children are included */
/* the fraction of the column's entries that are NULL: */
float4 stanullfrac;
/*
* stawidth is the average width in bytes of non-null entries. For
* fixed-width datatypes this is of course the same as the typlen, but for
* var-width types it is more useful. Note that this is the average width
* of the data as actually stored, post-TOASTing (eg, for a
* moved-out-of-line value, only the size of the pointer object is
* counted). This is the appropriate definition for the primary use of
* the statistic, which is to estimate sizes of in-memory hash tables of
* tuples.
*/
int32 stawidth;
/* ----------------
* stadistinct indicates the (approximate) number of distinct non-null
* data values in the column. The interpretation is:
* 0 unknown or not computed
* > 0 actual number of distinct values
* < 0 negative of multiplier for number of rows
* The special negative case allows us to cope with columns that are
* unique (stadistinct = -1) or nearly so (for example, a column in which
* non-null values appear about twice on the average could be represented
* by stadistinct = -0.5 if there are no nulls, or -0.4 if 20% of the
* column is nulls). Because the number-of-rows statistic in pg_class may
* be updated more frequently than pg_statistic is, it's important to be
* able to describe such situations as a multiple of the number of rows,
* rather than a fixed number of distinct values. But in other cases a
* fixed number is correct (eg, a boolean column).
* ----------------
*/
float4 stadistinct;
/* ----------------
* To allow keeping statistics on different kinds of datatypes,
* we do not hard-wire any particular meaning for the remaining
* statistical fields. Instead, we provide several "slots" in which
* statistical data can be placed. Each slot includes:
* kind integer code identifying kind of data (see below)
* op OID of associated operator, if needed
* numbers float4 array (for statistical values)
* values anyarray (for representations of data values)
* The ID and operator fields are never NULL; they are zeroes in an
* unused slot. The numbers and values fields are NULL in an unused
* slot, and might also be NULL in a used slot if the slot kind has
* no need for one or the other.
* ----------------
*/
int16 stakind1;
int16 stakind2;
int16 stakind3;
int16 stakind4;
int16 stakind5;
Oid staop1;
Oid staop2;
Oid staop3;
Oid staop4;
Oid staop5;
#ifdef CATALOG_VARLEN /* variable-length fields start here */
float4 stanumbers1[1];
float4 stanumbers2[1];
float4 stanumbers3[1];
float4 stanumbers4[1];
float4 stanumbers5[1];
/*
* Values in these arrays are values of the column's data type, or of some
* related type such as an array element type. We presently have to cheat
* quite a bit to allow polymorphic arrays of this kind, but perhaps
* someday it'll be a less bogus facility.
*/
anyarray stavalues1;
anyarray stavalues2;
anyarray stavalues3;
anyarray stavalues4;
anyarray stavalues5;
#endif
} FormData_pg_statistic;
#define STATISTIC_NUM_SLOTS 5
/* ----------------
* Form_pg_statistic corresponds to a pointer to a tuple with
* the format of pg_statistic relation.
* ----------------
*/
typedef FormData_pg_statistic *Form_pg_statistic;
/* ----------------
* compiler constants for pg_statistic
* ----------------
*/
#define Natts_pg_statistic 26
#define Anum_pg_statistic_starelid 1
#define Anum_pg_statistic_staattnum 2
#define Anum_pg_statistic_stainherit 3
#define Anum_pg_statistic_stanullfrac 4
#define Anum_pg_statistic_stawidth 5
#define Anum_pg_statistic_stadistinct 6
#define Anum_pg_statistic_stakind1 7
#define Anum_pg_statistic_stakind2 8
#define Anum_pg_statistic_stakind3 9
#define Anum_pg_statistic_stakind4 10
#define Anum_pg_statistic_stakind5 11
#define Anum_pg_statistic_staop1 12
#define Anum_pg_statistic_staop2 13
#define Anum_pg_statistic_staop3 14
#define Anum_pg_statistic_staop4 15
#define Anum_pg_statistic_staop5 16
#define Anum_pg_statistic_stanumbers1 17
#define Anum_pg_statistic_stanumbers2 18
#define Anum_pg_statistic_stanumbers3 19
#define Anum_pg_statistic_stanumbers4 20
#define Anum_pg_statistic_stanumbers5 21
#define Anum_pg_statistic_stavalues1 22
#define Anum_pg_statistic_stavalues2 23
#define Anum_pg_statistic_stavalues3 24
#define Anum_pg_statistic_stavalues4 25
#define Anum_pg_statistic_stavalues5 26
/*
* Currently, five statistical slot "kinds" are defined by core PostgreSQL,
* as documented below. Additional "kinds" will probably appear in
* future to help cope with non-scalar datatypes. Also, custom data types
* can define their own "kind" codes by mutual agreement between a custom
* typanalyze routine and the selectivity estimation functions of the type's
* operators.
*
* Code reading the pg_statistic relation should not assume that a particular
* data "kind" will appear in any particular slot. Instead, search the
* stakind fields to see if the desired data is available. (The standard
* function get_attstatsslot() may be used for this.)
*/
/*
* The present allocation of "kind" codes is:
*
* 1-99: reserved for assignment by the core PostgreSQL project
* (values in this range will be documented in this file)
* 100-199: reserved for assignment by the PostGIS project
* (values to be documented in PostGIS documentation)
* 200-299: reserved for assignment by the ESRI ST_Geometry project
* (values to be documented in ESRI ST_Geometry documentation)
* 300-9999: reserved for future public assignments
*
* For private use you may choose a "kind" code at random in the range
* 10000-30000. However, for code that is to be widely disseminated it is
* better to obtain a publicly defined "kind" code by request from the
* PostgreSQL Global Development Group.
*/
/*
* In a "most common values" slot, staop is the OID of the "=" operator
* used to decide whether values are the same or not. stavalues contains
* the K most common non-null values appearing in the column, and stanumbers
* contains their frequencies (fractions of total row count). The values
* shall be ordered in decreasing frequency. Note that since the arrays are
* variable-size, K may be chosen by the statistics collector. Values should
* not appear in MCV unless they have been observed to occur more than once;
* a unique column will have no MCV slot.
*/
#define STATISTIC_KIND_MCV 1
/*
* A "histogram" slot describes the distribution of scalar data. staop is
* the OID of the "<" operator that describes the sort ordering. (In theory,
* more than one histogram could appear, if a datatype has more than one
* useful sort operator.) stavalues contains M (>=2) non-null values that
* divide the non-null column data values into M-1 bins of approximately equal
* population. The first stavalues item is the MIN and the last is the MAX.
* stanumbers is not used and should be NULL. IMPORTANT POINT: if an MCV
* slot is also provided, then the histogram describes the data distribution
* *after removing the values listed in MCV* (thus, it's a "compressed
* histogram" in the technical parlance). This allows a more accurate
* representation of the distribution of a column with some very-common
* values. In a column with only a few distinct values, it's possible that
* the MCV list describes the entire data population; in this case the
* histogram reduces to empty and should be omitted.
*/
#define STATISTIC_KIND_HISTOGRAM 2
/*
* A "correlation" slot describes the correlation between the physical order
* of table tuples and the ordering of data values of this column, as seen
* by the "<" operator identified by staop. (As with the histogram, more
* than one entry could theoretically appear.) stavalues is not used and
* should be NULL. stanumbers contains a single entry, the correlation
* coefficient between the sequence of data values and the sequence of
* their actual tuple positions. The coefficient ranges from +1 to -1.
*/
#define STATISTIC_KIND_CORRELATION 3
/*
* A "most common elements" slot is similar to a "most common values" slot,
* except that it stores the most common non-null *elements* of the column
* values. This is useful when the column datatype is an array or some other
* type with identifiable elements (for instance, tsvector). staop contains
* the equality operator appropriate to the element type. stavalues contains
* the most common element values, and stanumbers their frequencies. Unlike
* MCV slots, frequencies are measured as the fraction of non-null rows the
* element value appears in, not the frequency of all rows. Also unlike
* MCV slots, the values are sorted into the element type's default order
* (to support binary search for a particular value). Since this puts the
* minimum and maximum frequencies at unpredictable spots in stanumbers,
* there are two extra members of stanumbers, holding copies of the minimum
* and maximum frequencies. Optionally, there can be a third extra member,
* which holds the frequency of null elements (expressed in the same terms:
* the fraction of non-null rows that contain at least one null element). If
* this member is omitted, the column is presumed to contain no null elements.
*
* Note: in current usage for tsvector columns, the stavalues elements are of
* type text, even though their representation within tsvector is not
* exactly text.
*/
#define STATISTIC_KIND_MCELEM 4
/*
* A "distinct elements count histogram" slot describes the distribution of
* the number of distinct element values present in each row of an array-type
* column. Only non-null rows are considered, and only non-null elements.
* staop contains the equality operator appropriate to the element type.
* stavalues is not used and should be NULL. The last member of stanumbers is
* the average count of distinct element values over all non-null rows. The
* preceding M (>=2) members form a histogram that divides the population of
* distinct-elements counts into M-1 bins of approximately equal population.
* The first of these is the minimum observed count, and the last the maximum.
*/
#define STATISTIC_KIND_DECHIST 5
/*
* A "length histogram" slot describes the distribution of range lengths in
* rows of a range-type column. stanumbers contains a single entry, the
* fraction of empty ranges. stavalues is a histogram of non-empty lengths, in
* a format similar to STATISTIC_KIND_HISTOGRAM: it contains M (>=2) range
* values that divide the column data values into M-1 bins of approximately
* equal population. The lengths are stored as float8s, as measured by the
* range type's subdiff function. Only non-null rows are considered.
*/
#define STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM 6
/*
* A "bounds histogram" slot is similar to STATISTIC_KIND_HISTOGRAM, but for
* a range-type column. stavalues contains M (>=2) range values that divide
* the column data values into M-1 bins of approximately equal population.
* Unlike a regular scalar histogram, this is actually two histograms combined
* into a single array, with the lower bounds of each value forming a
* histogram of lower bounds, and the upper bounds a histogram of upper
* bounds. Only non-NULL, non-empty ranges are included.
*/
#define STATISTIC_KIND_BOUNDS_HISTOGRAM 7
#endif /* PG_STATISTIC_H */
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