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293 lines
12 KiB
C
293 lines
12 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_statistic.h
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* definition of the system "statistic" relation (pg_statistic)
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* along with the relation's initial contents.
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*
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*
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* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/catalog/pg_statistic.h
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*
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* NOTES
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* the genbki.pl script reads this file and generates .bki
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* information from the DATA() statements.
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_STATISTIC_H
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#define PG_STATISTIC_H
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#include "catalog/genbki.h"
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/* ----------------
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* pg_statistic definition. cpp turns this into
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* typedef struct FormData_pg_statistic
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* ----------------
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*/
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#define StatisticRelationId 2619
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CATALOG(pg_statistic,2619) BKI_WITHOUT_OIDS
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{
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/* These fields form the unique key for the entry: */
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Oid starelid; /* relation containing attribute */
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int16 staattnum; /* attribute (column) stats are for */
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bool stainherit; /* true if inheritance children are included */
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/* the fraction of the column's entries that are NULL: */
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float4 stanullfrac;
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/*
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* stawidth is the average width in bytes of non-null entries. For
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* fixed-width datatypes this is of course the same as the typlen, but for
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* var-width types it is more useful. Note that this is the average width
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* of the data as actually stored, post-TOASTing (eg, for a
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* moved-out-of-line value, only the size of the pointer object is
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* counted). This is the appropriate definition for the primary use of
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* the statistic, which is to estimate sizes of in-memory hash tables of
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* tuples.
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*/
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int32 stawidth;
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/* ----------------
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* stadistinct indicates the (approximate) number of distinct non-null
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* data values in the column. The interpretation is:
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* 0 unknown or not computed
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* > 0 actual number of distinct values
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* < 0 negative of multiplier for number of rows
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* The special negative case allows us to cope with columns that are
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* unique (stadistinct = -1) or nearly so (for example, a column in
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* which values appear about twice on the average could be represented
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* by stadistinct = -0.5). Because the number-of-rows statistic in
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* pg_class may be updated more frequently than pg_statistic is, it's
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* important to be able to describe such situations as a multiple of
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* the number of rows, rather than a fixed number of distinct values.
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* But in other cases a fixed number is correct (eg, a boolean column).
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* ----------------
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*/
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float4 stadistinct;
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/* ----------------
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* To allow keeping statistics on different kinds of datatypes,
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* we do not hard-wire any particular meaning for the remaining
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* statistical fields. Instead, we provide several "slots" in which
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* statistical data can be placed. Each slot includes:
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* kind integer code identifying kind of data (see below)
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* op OID of associated operator, if needed
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* numbers float4 array (for statistical values)
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* values anyarray (for representations of data values)
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* The ID and operator fields are never NULL; they are zeroes in an
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* unused slot. The numbers and values fields are NULL in an unused
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* slot, and might also be NULL in a used slot if the slot kind has
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* no need for one or the other.
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* ----------------
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*/
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int16 stakind1;
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int16 stakind2;
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int16 stakind3;
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int16 stakind4;
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int16 stakind5;
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Oid staop1;
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Oid staop2;
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Oid staop3;
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Oid staop4;
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Oid staop5;
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#ifdef CATALOG_VARLEN /* variable-length fields start here */
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float4 stanumbers1[1];
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float4 stanumbers2[1];
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float4 stanumbers3[1];
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float4 stanumbers4[1];
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float4 stanumbers5[1];
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/*
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* Values in these arrays are values of the column's data type, or of some
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* related type such as an array element type. We presently have to cheat
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* quite a bit to allow polymorphic arrays of this kind, but perhaps
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* someday it'll be a less bogus facility.
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*/
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anyarray stavalues1;
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anyarray stavalues2;
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anyarray stavalues3;
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anyarray stavalues4;
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anyarray stavalues5;
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#endif
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} FormData_pg_statistic;
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#define STATISTIC_NUM_SLOTS 5
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/* ----------------
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* Form_pg_statistic corresponds to a pointer to a tuple with
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* the format of pg_statistic relation.
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* ----------------
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*/
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typedef FormData_pg_statistic *Form_pg_statistic;
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/* ----------------
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* compiler constants for pg_statistic
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* ----------------
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*/
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#define Natts_pg_statistic 26
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#define Anum_pg_statistic_starelid 1
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#define Anum_pg_statistic_staattnum 2
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#define Anum_pg_statistic_stainherit 3
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#define Anum_pg_statistic_stanullfrac 4
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#define Anum_pg_statistic_stawidth 5
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#define Anum_pg_statistic_stadistinct 6
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#define Anum_pg_statistic_stakind1 7
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#define Anum_pg_statistic_stakind2 8
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#define Anum_pg_statistic_stakind3 9
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#define Anum_pg_statistic_stakind4 10
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#define Anum_pg_statistic_stakind5 11
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#define Anum_pg_statistic_staop1 12
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#define Anum_pg_statistic_staop2 13
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#define Anum_pg_statistic_staop3 14
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#define Anum_pg_statistic_staop4 15
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#define Anum_pg_statistic_staop5 16
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#define Anum_pg_statistic_stanumbers1 17
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#define Anum_pg_statistic_stanumbers2 18
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#define Anum_pg_statistic_stanumbers3 19
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#define Anum_pg_statistic_stanumbers4 20
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#define Anum_pg_statistic_stanumbers5 21
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#define Anum_pg_statistic_stavalues1 22
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#define Anum_pg_statistic_stavalues2 23
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#define Anum_pg_statistic_stavalues3 24
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#define Anum_pg_statistic_stavalues4 25
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#define Anum_pg_statistic_stavalues5 26
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/*
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* Currently, five statistical slot "kinds" are defined by core PostgreSQL,
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* as documented below. Additional "kinds" will probably appear in
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* future to help cope with non-scalar datatypes. Also, custom data types
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* can define their own "kind" codes by mutual agreement between a custom
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* typanalyze routine and the selectivity estimation functions of the type's
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* operators.
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*
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* Code reading the pg_statistic relation should not assume that a particular
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* data "kind" will appear in any particular slot. Instead, search the
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* stakind fields to see if the desired data is available. (The standard
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* function get_attstatsslot() may be used for this.)
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*/
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/*
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* The present allocation of "kind" codes is:
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*
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* 1-99: reserved for assignment by the core PostgreSQL project
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* (values in this range will be documented in this file)
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* 100-199: reserved for assignment by the PostGIS project
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* (values to be documented in PostGIS documentation)
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* 200-299: reserved for assignment by the ESRI ST_Geometry project
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* (values to be documented in ESRI ST_Geometry documentation)
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* 300-9999: reserved for future public assignments
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*
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* For private use you may choose a "kind" code at random in the range
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* 10000-30000. However, for code that is to be widely disseminated it is
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* better to obtain a publicly defined "kind" code by request from the
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* PostgreSQL Global Development Group.
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*/
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/*
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* In a "most common values" slot, staop is the OID of the "=" operator
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* used to decide whether values are the same or not. stavalues contains
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* the K most common non-null values appearing in the column, and stanumbers
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* contains their frequencies (fractions of total row count). The values
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* shall be ordered in decreasing frequency. Note that since the arrays are
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* variable-size, K may be chosen by the statistics collector. Values should
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* not appear in MCV unless they have been observed to occur more than once;
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* a unique column will have no MCV slot.
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*/
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#define STATISTIC_KIND_MCV 1
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/*
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* A "histogram" slot describes the distribution of scalar data. staop is
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* the OID of the "<" operator that describes the sort ordering. (In theory,
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* more than one histogram could appear, if a datatype has more than one
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* useful sort operator.) stavalues contains M (>=2) non-null values that
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* divide the non-null column data values into M-1 bins of approximately equal
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* population. The first stavalues item is the MIN and the last is the MAX.
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* stanumbers is not used and should be NULL. IMPORTANT POINT: if an MCV
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* slot is also provided, then the histogram describes the data distribution
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* *after removing the values listed in MCV* (thus, it's a "compressed
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* histogram" in the technical parlance). This allows a more accurate
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* representation of the distribution of a column with some very-common
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* values. In a column with only a few distinct values, it's possible that
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* the MCV list describes the entire data population; in this case the
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* histogram reduces to empty and should be omitted.
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*/
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#define STATISTIC_KIND_HISTOGRAM 2
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/*
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* A "correlation" slot describes the correlation between the physical order
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* of table tuples and the ordering of data values of this column, as seen
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* by the "<" operator identified by staop. (As with the histogram, more
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* than one entry could theoretically appear.) stavalues is not used and
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* should be NULL. stanumbers contains a single entry, the correlation
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* coefficient between the sequence of data values and the sequence of
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* their actual tuple positions. The coefficient ranges from +1 to -1.
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*/
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#define STATISTIC_KIND_CORRELATION 3
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/*
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* A "most common elements" slot is similar to a "most common values" slot,
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* except that it stores the most common non-null *elements* of the column
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* values. This is useful when the column datatype is an array or some other
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* type with identifiable elements (for instance, tsvector). staop contains
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* the equality operator appropriate to the element type. stavalues contains
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* the most common element values, and stanumbers their frequencies. Unlike
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* MCV slots, frequencies are measured as the fraction of non-null rows the
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* element value appears in, not the frequency of all rows. Also unlike
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* MCV slots, the values are sorted into the element type's default order
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* (to support binary search for a particular value). Since this puts the
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* minimum and maximum frequencies at unpredictable spots in stanumbers,
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* there are two extra members of stanumbers, holding copies of the minimum
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* and maximum frequencies. Optionally, there can be a third extra member,
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* which holds the frequency of null elements (expressed in the same terms:
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* the fraction of non-null rows that contain at least one null element). If
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* this member is omitted, the column is presumed to contain no null elements.
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*
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* Note: in current usage for tsvector columns, the stavalues elements are of
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* type text, even though their representation within tsvector is not
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* exactly text.
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*/
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#define STATISTIC_KIND_MCELEM 4
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/*
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* A "distinct elements count histogram" slot describes the distribution of
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* the number of distinct element values present in each row of an array-type
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* column. Only non-null rows are considered, and only non-null elements.
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* staop contains the equality operator appropriate to the element type.
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* stavalues is not used and should be NULL. The last member of stanumbers is
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* the average count of distinct element values over all non-null rows. The
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* preceding M (>=2) members form a histogram that divides the population of
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* distinct-elements counts into M-1 bins of approximately equal population.
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* The first of these is the minimum observed count, and the last the maximum.
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*/
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#define STATISTIC_KIND_DECHIST 5
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/*
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* A "length histogram" slot describes the distribution of range lengths in
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* rows of a range-type column. stanumbers contains a single entry, the
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* fraction of empty ranges. stavalues is a histogram of non-empty lengths, in
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* a format similar to STATISTIC_KIND_HISTOGRAM: it contains M (>=2) range
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* values that divide the column data values into M-1 bins of approximately
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* equal population. The lengths are stores as float8s, as measured by the
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* range type's subdiff function. Only non-null rows are considered.
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*/
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#define STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM 6
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/*
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* A "bounds histogram" slot is similar to STATISTIC_KIND_HISTOGRAM, but for
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* a range-type column. stavalues contains M (>=2) range values that divide
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* the column data values into M-1 bins of approximately equal population.
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* Unlike a regular scalar histogram, this is actually two histograms combined
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* into a single array, with the lower bounds of each value forming a
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* histogram of lower bounds, and the upper bounds a histogram of upper
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* bounds. Only non-NULL, non-empty ranges are included.
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*/
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#define STATISTIC_KIND_BOUNDS_HISTOGRAM 7
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#endif /* PG_STATISTIC_H */
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