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pg_statistic.h
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1 /*-------------------------------------------------------------------------
2  *
3  * pg_statistic.h
4  * definition of the system "statistic" relation (pg_statistic)
5  * along with the relation's initial contents.
6  *
7  *
8  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
9  * Portions Copyright (c) 1994, Regents of the University of California
10  *
11  * src/include/catalog/pg_statistic.h
12  *
13  * NOTES
14  * the genbki.pl script reads this file and generates .bki
15  * information from the DATA() statements.
16  *
17  *-------------------------------------------------------------------------
18  */
19 #ifndef PG_STATISTIC_H
20 #define PG_STATISTIC_H
21 
22 #include "catalog/genbki.h"
23 
24 /* ----------------
25  * pg_statistic definition. cpp turns this into
26  * typedef struct FormData_pg_statistic
27  * ----------------
28  */
29 #define StatisticRelationId 2619
30 
31 CATALOG(pg_statistic,2619) BKI_WITHOUT_OIDS
32 {
33  /* These fields form the unique key for the entry: */
34  Oid starelid; /* relation containing attribute */
35  int16 staattnum; /* attribute (column) stats are for */
36  bool stainherit; /* true if inheritance children are included */
37 
38  /* the fraction of the column's entries that are NULL: */
39  float4 stanullfrac;
40 
41  /*
42  * stawidth is the average width in bytes of non-null entries. For
43  * fixed-width datatypes this is of course the same as the typlen, but for
44  * var-width types it is more useful. Note that this is the average width
45  * of the data as actually stored, post-TOASTing (eg, for a
46  * moved-out-of-line value, only the size of the pointer object is
47  * counted). This is the appropriate definition for the primary use of
48  * the statistic, which is to estimate sizes of in-memory hash tables of
49  * tuples.
50  */
51  int32 stawidth;
52 
53  /* ----------------
54  * stadistinct indicates the (approximate) number of distinct non-null
55  * data values in the column. The interpretation is:
56  * 0 unknown or not computed
57  * > 0 actual number of distinct values
58  * < 0 negative of multiplier for number of rows
59  * The special negative case allows us to cope with columns that are
60  * unique (stadistinct = -1) or nearly so (for example, a column in which
61  * non-null values appear about twice on the average could be represented
62  * by stadistinct = -0.5 if there are no nulls, or -0.4 if 20% of the
63  * column is nulls). Because the number-of-rows statistic in pg_class may
64  * be updated more frequently than pg_statistic is, it's important to be
65  * able to describe such situations as a multiple of the number of rows,
66  * rather than a fixed number of distinct values. But in other cases a
67  * fixed number is correct (eg, a boolean column).
68  * ----------------
69  */
70  float4 stadistinct;
71 
72  /* ----------------
73  * To allow keeping statistics on different kinds of datatypes,
74  * we do not hard-wire any particular meaning for the remaining
75  * statistical fields. Instead, we provide several "slots" in which
76  * statistical data can be placed. Each slot includes:
77  * kind integer code identifying kind of data (see below)
78  * op OID of associated operator, if needed
79  * numbers float4 array (for statistical values)
80  * values anyarray (for representations of data values)
81  * The ID and operator fields are never NULL; they are zeroes in an
82  * unused slot. The numbers and values fields are NULL in an unused
83  * slot, and might also be NULL in a used slot if the slot kind has
84  * no need for one or the other.
85  * ----------------
86  */
87 
88  int16 stakind1;
89  int16 stakind2;
90  int16 stakind3;
91  int16 stakind4;
92  int16 stakind5;
93 
94  Oid staop1;
95  Oid staop2;
96  Oid staop3;
97  Oid staop4;
98  Oid staop5;
99 
100 #ifdef CATALOG_VARLEN /* variable-length fields start here */
101  float4 stanumbers1[1];
102  float4 stanumbers2[1];
103  float4 stanumbers3[1];
104  float4 stanumbers4[1];
105  float4 stanumbers5[1];
106 
107  /*
108  * Values in these arrays are values of the column's data type, or of some
109  * related type such as an array element type. We presently have to cheat
110  * quite a bit to allow polymorphic arrays of this kind, but perhaps
111  * someday it'll be a less bogus facility.
112  */
113  anyarray stavalues1;
114  anyarray stavalues2;
115  anyarray stavalues3;
116  anyarray stavalues4;
117  anyarray stavalues5;
118 #endif
120 
121 #define STATISTIC_NUM_SLOTS 5
122 
123 
124 /* ----------------
125  * Form_pg_statistic corresponds to a pointer to a tuple with
126  * the format of pg_statistic relation.
127  * ----------------
128  */
130 
131 /* ----------------
132  * compiler constants for pg_statistic
133  * ----------------
134  */
135 #define Natts_pg_statistic 26
136 #define Anum_pg_statistic_starelid 1
137 #define Anum_pg_statistic_staattnum 2
138 #define Anum_pg_statistic_stainherit 3
139 #define Anum_pg_statistic_stanullfrac 4
140 #define Anum_pg_statistic_stawidth 5
141 #define Anum_pg_statistic_stadistinct 6
142 #define Anum_pg_statistic_stakind1 7
143 #define Anum_pg_statistic_stakind2 8
144 #define Anum_pg_statistic_stakind3 9
145 #define Anum_pg_statistic_stakind4 10
146 #define Anum_pg_statistic_stakind5 11
147 #define Anum_pg_statistic_staop1 12
148 #define Anum_pg_statistic_staop2 13
149 #define Anum_pg_statistic_staop3 14
150 #define Anum_pg_statistic_staop4 15
151 #define Anum_pg_statistic_staop5 16
152 #define Anum_pg_statistic_stanumbers1 17
153 #define Anum_pg_statistic_stanumbers2 18
154 #define Anum_pg_statistic_stanumbers3 19
155 #define Anum_pg_statistic_stanumbers4 20
156 #define Anum_pg_statistic_stanumbers5 21
157 #define Anum_pg_statistic_stavalues1 22
158 #define Anum_pg_statistic_stavalues2 23
159 #define Anum_pg_statistic_stavalues3 24
160 #define Anum_pg_statistic_stavalues4 25
161 #define Anum_pg_statistic_stavalues5 26
162 
163 /*
164  * Currently, five statistical slot "kinds" are defined by core PostgreSQL,
165  * as documented below. Additional "kinds" will probably appear in
166  * future to help cope with non-scalar datatypes. Also, custom data types
167  * can define their own "kind" codes by mutual agreement between a custom
168  * typanalyze routine and the selectivity estimation functions of the type's
169  * operators.
170  *
171  * Code reading the pg_statistic relation should not assume that a particular
172  * data "kind" will appear in any particular slot. Instead, search the
173  * stakind fields to see if the desired data is available. (The standard
174  * function get_attstatsslot() may be used for this.)
175  */
176 
177 /*
178  * The present allocation of "kind" codes is:
179  *
180  * 1-99: reserved for assignment by the core PostgreSQL project
181  * (values in this range will be documented in this file)
182  * 100-199: reserved for assignment by the PostGIS project
183  * (values to be documented in PostGIS documentation)
184  * 200-299: reserved for assignment by the ESRI ST_Geometry project
185  * (values to be documented in ESRI ST_Geometry documentation)
186  * 300-9999: reserved for future public assignments
187  *
188  * For private use you may choose a "kind" code at random in the range
189  * 10000-30000. However, for code that is to be widely disseminated it is
190  * better to obtain a publicly defined "kind" code by request from the
191  * PostgreSQL Global Development Group.
192  */
193 
194 /*
195  * In a "most common values" slot, staop is the OID of the "=" operator
196  * used to decide whether values are the same or not. stavalues contains
197  * the K most common non-null values appearing in the column, and stanumbers
198  * contains their frequencies (fractions of total row count). The values
199  * shall be ordered in decreasing frequency. Note that since the arrays are
200  * variable-size, K may be chosen by the statistics collector. Values should
201  * not appear in MCV unless they have been observed to occur more than once;
202  * a unique column will have no MCV slot.
203  */
204 #define STATISTIC_KIND_MCV 1
205 
206 /*
207  * A "histogram" slot describes the distribution of scalar data. staop is
208  * the OID of the "<" operator that describes the sort ordering. (In theory,
209  * more than one histogram could appear, if a datatype has more than one
210  * useful sort operator.) stavalues contains M (>=2) non-null values that
211  * divide the non-null column data values into M-1 bins of approximately equal
212  * population. The first stavalues item is the MIN and the last is the MAX.
213  * stanumbers is not used and should be NULL. IMPORTANT POINT: if an MCV
214  * slot is also provided, then the histogram describes the data distribution
215  * *after removing the values listed in MCV* (thus, it's a "compressed
216  * histogram" in the technical parlance). This allows a more accurate
217  * representation of the distribution of a column with some very-common
218  * values. In a column with only a few distinct values, it's possible that
219  * the MCV list describes the entire data population; in this case the
220  * histogram reduces to empty and should be omitted.
221  */
222 #define STATISTIC_KIND_HISTOGRAM 2
223 
224 /*
225  * A "correlation" slot describes the correlation between the physical order
226  * of table tuples and the ordering of data values of this column, as seen
227  * by the "<" operator identified by staop. (As with the histogram, more
228  * than one entry could theoretically appear.) stavalues is not used and
229  * should be NULL. stanumbers contains a single entry, the correlation
230  * coefficient between the sequence of data values and the sequence of
231  * their actual tuple positions. The coefficient ranges from +1 to -1.
232  */
233 #define STATISTIC_KIND_CORRELATION 3
234 
235 /*
236  * A "most common elements" slot is similar to a "most common values" slot,
237  * except that it stores the most common non-null *elements* of the column
238  * values. This is useful when the column datatype is an array or some other
239  * type with identifiable elements (for instance, tsvector). staop contains
240  * the equality operator appropriate to the element type. stavalues contains
241  * the most common element values, and stanumbers their frequencies. Unlike
242  * MCV slots, frequencies are measured as the fraction of non-null rows the
243  * element value appears in, not the frequency of all rows. Also unlike
244  * MCV slots, the values are sorted into the element type's default order
245  * (to support binary search for a particular value). Since this puts the
246  * minimum and maximum frequencies at unpredictable spots in stanumbers,
247  * there are two extra members of stanumbers, holding copies of the minimum
248  * and maximum frequencies. Optionally, there can be a third extra member,
249  * which holds the frequency of null elements (expressed in the same terms:
250  * the fraction of non-null rows that contain at least one null element). If
251  * this member is omitted, the column is presumed to contain no null elements.
252  *
253  * Note: in current usage for tsvector columns, the stavalues elements are of
254  * type text, even though their representation within tsvector is not
255  * exactly text.
256  */
257 #define STATISTIC_KIND_MCELEM 4
258 
259 /*
260  * A "distinct elements count histogram" slot describes the distribution of
261  * the number of distinct element values present in each row of an array-type
262  * column. Only non-null rows are considered, and only non-null elements.
263  * staop contains the equality operator appropriate to the element type.
264  * stavalues is not used and should be NULL. The last member of stanumbers is
265  * the average count of distinct element values over all non-null rows. The
266  * preceding M (>=2) members form a histogram that divides the population of
267  * distinct-elements counts into M-1 bins of approximately equal population.
268  * The first of these is the minimum observed count, and the last the maximum.
269  */
270 #define STATISTIC_KIND_DECHIST 5
271 
272 /*
273  * A "length histogram" slot describes the distribution of range lengths in
274  * rows of a range-type column. stanumbers contains a single entry, the
275  * fraction of empty ranges. stavalues is a histogram of non-empty lengths, in
276  * a format similar to STATISTIC_KIND_HISTOGRAM: it contains M (>=2) range
277  * values that divide the column data values into M-1 bins of approximately
278  * equal population. The lengths are stores as float8s, as measured by the
279  * range type's subdiff function. Only non-null rows are considered.
280  */
281 #define STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM 6
282 
283 /*
284  * A "bounds histogram" slot is similar to STATISTIC_KIND_HISTOGRAM, but for
285  * a range-type column. stavalues contains M (>=2) range values that divide
286  * the column data values into M-1 bins of approximately equal population.
287  * Unlike a regular scalar histogram, this is actually two histograms combined
288  * into a single array, with the lower bounds of each value forming a
289  * histogram of lower bounds, and the upper bounds a histogram of upper
290  * bounds. Only non-NULL, non-empty ranges are included.
291  */
292 #define STATISTIC_KIND_BOUNDS_HISTOGRAM 7
293 
294 #endif /* PG_STATISTIC_H */
signed short int16
Definition: c.h:255
unsigned int Oid
Definition: postgres_ext.h:31
FormData_pg_statistic * Form_pg_statistic
Definition: pg_statistic.h:129
signed int int32
Definition: c.h:256
#define BKI_WITHOUT_OIDS
Definition: genbki.h:28
FormData_pg_statistic
Definition: pg_statistic.h:119
float float4
Definition: c.h:380
CATALOG(pg_statistic, 2619) BKI_WITHOUT_OIDS
Definition: pg_statistic.h:31