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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) 1996-2012, 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 */ int2 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. */ int4 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. * ---------------- */ int2 stakind1; int2 stakind2; int2 stakind3; int2 stakind4; int2 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 #endif /* PG_STATISTIC_H */